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      <title>Two-Year Outcome After Lumbar Microdiscectomy Versus Microscopic Sequestrectomy: Part 1: Evaluation of Clinical Outcome</title>
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<h3>Two-Year Outcome After Lumbar Microdiscectomy Versus Microscopic Sequestrectomy: Part 1: Evaluation of Clinical Outcome</h3>


<p>Barth, Martin MD;* Weiss, Christel MD;<sup>†</sup> Thomé, Claudius MD*</p>

<p>*Department of Neurosurgery, and <sup>†</sup>Institute for Medical Statistics, University Hospital Mannheim, Medical Faculty Mannheim of the Ruprecht-Karls-University of Heidelberg, Germany.</p>
<p>Acknowledgment date: March 29, 2007. Revision date: July 22, 2007. Acceptance date: August 6, 2007.</p>
<p>The manuscript submitted does not contain information about medical device(s)/drug(s).</p>
<p>No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.</p>
<p>Claudius Thomé, MD, Department of Neurosurgery, University Hospital Mannheim, Medical Faculty Mannheim of the Ruprecht-Karls-University of Heidelberg, Theodor-Kutzer-Ufer 1-3, D-68167 Mannheim, Germany; E-mail: claudius.thome@nch.ma.uni-heidelberg.de</p>




<h3>Abstract and Introduction</h3>

<h4>Abstract</h4>
<p>
   Study Design: Single-center randomized prospective study at a university hospital.

   Objective: The aim of the present study was to provide a 2-year outcome comparison of microdiscectomy (D) versus microscopic sequestrectomy (S) in terms of reherniation rates, clinical investigation, and self-rated parameters using a comprehensive questionnaire.

   Summary of Background Data: Simple fragment excision in cases of herniated lumbar discs has been repeatedly reported as an alternative to standard microdiscectomy, but prospective data with sufficient follow-up is lacking to date. Preliminary results of a prospective randomized study in patients with lumbar disc herniations indicated equal reherniation rates and a trend toward superior clinical results in patients undergoing only sequestrectomy after 4 to 6 months.

   Material and Methods: Eighty-four patients with lumbar disc herniations were treated with microdiscectomy or microscopic sequestrectomy in equal parts. Patients were re-evaluated thoroughly clinically after 2 years. Results of this investigation (low back pain, sciatica, motor-, sensory-, reflex-, straight leg raising test-indexes) and self-rated parameters including SF-36 were analyzed for differences between groups and between time points.

   Results: Thirty-eight (D) and 40 (S) patients were attainable for follow-up. Reherniation rates did not differ significantly (10.5%, group D; 12.5%, group S; P = 1.0). Following dramatic improvement after surgery in both groups, results of the clinical investigation remained stable over time without significant differences between groups. In contrast, self-rated assessment demonstrated clinical deterioration of the surgical results within the first 2 years after microdiscectomy, while they rather improved after sequestrectomy. Because of this development, the outcome measures at 2 years pointed in favor of sequestrectomy with results being significant for important parameters such as use of analgesics, performance, and overall outcome.

   Conclusion Reherniation rates within 2 years after sequestrectomy and microdiscectomy are comparable. However, outcome after microdiscectomy seems to worsen over time, whereas it remains stable after sequestrectomy. Thus, 2-year follow-up revealed clinical results favoring sequestrectomy. Performing sequestrectomy alone may therefore represent an advantageous alternative to standard microdiscectomy.

</p>

<h4>Introduction</h4>
<p>Lumbar disc herniation represents a common medical problem with numerous procedures being carried out in patients with intractable pain or severe neurological symptoms related to nerve root compression. Despite various techniques that have been developed for this indication, most patients still undergo the standard microdiscectomy as introduced by Yasargil or Caspar in 1977 using the interlaminar approach with partial resection of bony structures, the facet joints, and the ligamentum flavum followed by removal of intervertebral disc material.<sup>[1,2]</sup> This procedure has been modified to a more minimalist approach with minimal removal of bony and ligamentous structures.<sup>[3]</sup> In addition, in case of free herniated disc material it has been proposed to remove only the free fragments and tissue which can be easily mobilized from the intervertebral space. Since the introduction of this approach in 1978, several clinical studies have shown promising results without an increased incidence of reherniations.<sup>[4,5]</sup></p>
<p>In our previously published study, we prospectively compared microscopic sequestrectomy with microdiscectomy and found a comparable outcome of both approaches regarding pain and patient satisfaction after 4 to 6 months.<sup>[6]</sup> In contrast to previous studies, however, we not only included patients harboring freely herniated disc material but also patients with subligamentary and transannular herniations, thus augmenting the role of sequestrectomy. Although an increase in reherniations after simple sequestrectomy has dogmatically been brought up by the opponents of this approach,<sup>[7]</sup> other investigators have linked aggressive discectomy with accelerated segmental degeneration<sup>[8,9]</sup> and this may contribute to failed-back surgery syndrome after lumbar microdiscectomy.<sup>[5,10,11]</sup> Although reherniations are thought to occur in the early postoperative period,<sup>[4,7]</sup> further degeneration is expected thereafter. Thus, if removal of discal tissue has an impact on segmental degeneration, this should become more evident over time after microdiscectomy. On the other hand, late reherniations could cause a clinical deterioration after sequestrectomy.</p>
<p>The aim of the present follow-up study was therefore to investigate the further clinical course of either surgical groups and to statistically analyze the data not only between groups but also between time points to detect potential clinical deterioration.</p>

<h3>Clinical Materials and Methods</h3>

<h4>Study Population and Management</h4>
<p>This study is a follow-up study within the context of our previously published work<sup>[6]</sup> and has been approved by the local ethics committee. All patients from the initial study population, who had been surgically treated for a single-level lumbar disc herniation, were included. Patient inclusion criteria have been described previously. In brief, patients had to fulfill the following criteria: (1) virgin spines; (2) no emergency operation; (3) age above 18 and below 60; (4) sufficient knowledge of the German language to complete the questionnaires; (5) MRI-confirmed disc herniation; and (6) absence of concomitant spinal disease. In contrast to previous studies<sup>[3,5]</sup> not only cases with free fragments, but also subligamentary herniations and those still in continuity with the disc space (transannular herniations) were included.<sup>[6]</sup> After being randomized, patients received either a standard discectomy with removal of herniated material plus discal tissue from the intervertebral space (D) or a sequestrectomy with removal of the herniated material only (S). Unlike Williams, who removed tissue easy to mobilize from the intervertebral space,<sup>[3,4]</sup> the disc space was never entered in group S. In the case of transannular herniations where part of the fragment is still within the interspace, the fragment was grasped outside the interspace and removed in one piece without additionally entering the intervertebral space regardless of nucleus material visible in the disc space or a resulting large annular defect.</p>
<p>The procedures were performed by 2 surgeons who conducted both techniques in a standardized manner using an operating microscope (Carl Zeiss Co., Oberkochen, Germany). Discectomy included entering the disc space with a pituitary rongeur in an attempt to remove as much of the nucleus, i.e., the loose intradiscal tissue, as possible. Injury to the endplates and the annulus, however, was avoided, so that no curettes or other instruments were applied intradiscally. Thus, the central nucleectomy represents the actual difference between the procedures.</p>

<h4>Assessment of Outcome</h4>
<p>The number and dates of reherniations were documented for each group from all patients attainable via telephone interview or follow-up visit. Clinical outcome was assessed via follow-up visits. Latest follow-up was conducted 2 years after surgery. Patients who refused to participate in follow-up visits or who were lost to follow-up were excluded from the analysis of clinical parameters. Reoperations were performed in cases of symptomatic reherniations, and these patients were included in the clinical follow-up evaluation.</p>
<p>In the course of a follow-up visit each patient underwent (1) a clinical neurological investigation focusing on the lower limbs. It consisted of (A) the strength of the most affected muscle, which was graded with a range from 0 (no contraction) to 5 (full strength) and (B) the sensory index that graded sensory dysfunction in 1 (normal), 2 (slight deficit), or 3 (severe deficit). Furthermore, (C) the straight leg raising test (SLR) was assessed as 1 (61-90°; negative), 2 (41-60°; moderately positive), or 3 (0-40°; positive). Finally, (D) the reflex index (RI) was determined. The grading results of 3 different reflexes (adductor-, patellar-, and ankle-jerk reflex) with 1 (absent), 2 (weaker as contralateral), and 3 (normal) are summed up and divided with 3 according to the formula [(Σ reflexes 1-3)/3] with a maximum value of 3.</p>
<p>In addition to the clinical investigation, all patients completed an extensive standardized questionnaire in which they were asked (2) to rate pain intensity for the lower back and the leg(s) during the last 5 days according the visual analog scale ranging from 0 to 10; (3) to document relieve of symptoms compared with preoperative (sensory deficit, motor deficit). The grading for each symptom ranged from 1 (much better) to 5 (much worse). To get a general idea to what extent patients are still affected, they documented (4) impairment in activities of daily living, impairment of sleep, work, or sport, physician consultations, and the extent of pain-related drug use. For analysis, answers were again graded ( <a href="#">Table 2</a> ). Additionally, the (5) performance (1 = much better to 4 = worse) and the (6) overall outcome (1 = much better to 4 = worse) were rated. Patient satisfaction was assessed using the (7) patient satisfaction index,<sup>[12,13]</sup> graded from 1 (surgery met my expectations) to 4 (I am the same or worse as compared to before surgery). Functional and economic status was investigated using (8) the Prolo score.<sup>[14]</sup> Finally, (9) health-related quality-of-life was assessed using the MOS-36 item short form health survey (SF-36).</p>

!!! TABLE 2

<h4>Statistical Analysis</h4>
<p>Before the start of the study a power analysis was performed. For simplification, the 4-scale primary outcome measures (overall outcome, performance) were interpreted as quantitative data and a difference of 0.5 points between groups was defined as clinically relevant. Considering the standard deviation derived from previous follow-up data after disc surgery, 31 patients would be required to detect this difference with 80% power at the 0.05 level. To take into account that the outcome data are ordinal and not quantitative, patient recruitment was aimed at 40 patients.</p>
<p>The Fisher exact test was used to compare patient characteristics. For the parameters LBP, sciatica, motor and sensory function, SLR, and reflex index intergroup differences at 3 time points [preoperative, early (4-6 months), and late (24 months) follow-up] were evaluated using the Cochran-Armitage Trend Test. Time-dependent changes within each group were assessed using the Wilcoxon signed rank test. To adjust for confounding factors a logistic regression using a multiple model with ordered categories was performed (alpha level = 0.10; SAS software, release 8.02; SAS Institute Inc., Cary). Wald's test was used to test which variables, like patient's gender or surgeon, had a statistically significant influence on outcome. To enable the comparison of the SF-36 results across the entire SF-36 profile with the German reference population, aged 45 to 65 years,<sup>[15]</sup> percentage changes of the mean values of both study groups to the reference population were calculated. Statistical significance was set at a probability value of less than 0.05.</p>

<h3>Results</h3>

<h4>Patient Characteristics</h4>
<p>Of 42 initially randomized patients for each group, 38 of group D and 40 of group S were attainable via telephone or personally during follow-up visits (78 in total; 93%). From these patients, 10.5% after discectomy and 12.5% after sequestrectomy suffered reherniations at levels as indicated in ( <a href="#">Table 1</a> ) (NS). Seventy-three patients sufficiently complied with the standardized clinical investigation and adequately answered the questionnaires. Follow-up time of these patients ranged from 18 to 29 months. Patient characteristics did not differ significantly and are summarized in ( <a href="#">Table 1</a> ).</p>

!!! TABLE 1

<p>Ordinal logistic regression did reveal that preoperative low back pain (LBP) was influenced by gender (P = 0.026). Postoperative scores and outcome variables were not found to be influenced by confounding factors.</p>

<h4>Pain</h4>
<p>LBP after 2 years was reduced to 2.9 ± 2.6 in group D and to 1.8 ± 1.9 in group S, whereas sciatica almost diminished to 1.6 ± 2.4 (D) and to 1.2 ± 1.8 (S). Viewing all time points separately (before surgery, early, and late follow-up), there were no significant differences between groups D and S regarding the intensity of LBP and sciatica (P &gt; 0.05; Trend test). Compared with before surgery, both study groups experienced significant pain relief at the 2 postoperative visits for LBP and for sciatica (P &lt; 0.0001; Wilcoxon signed rank test). Comparing both postoperative visits, no significant changes occurred in both groups regarding LBP or sciatica (group D: P = 0.243, LBP; P = 0.815, sciatica; group S: P = 0.562, LBP; P = 0.517, sciatica; Wilcoxon signed rank test).</p>

<h4>Clinical Investigation</h4>
<p>Motor grades (MG), sensory-index (SI), SLR, and RI showed positive courses with rapid postoperative improvement for both groups (Figure 1). All parameters revealed no significant intergroup differences at corresponding time points (all P-values ≥ 0.278; Trend test). Apart from the RI all indexes were improved significantly at early follow-up and remained significantly improved compared with preoperative levels. In the late postoperative course, i.e., between the first and the second follow-up, no significant changes were detectable for all parameters within each group (group D: P = 0.688, MG; P = 0.508, SI; P = 0.375, SLR; P = 0.774, RI; group S: P = 0.062, MG; P = 1.000, SI; P = 0.469, SLR; P = 0.234, RI; Wilcoxon signed rank test) and between both groups (P = 0.053, MG; P = 0.309, SI; P = 0.870, SLR; P = 0.529, RI; Trend test).</p>

!!! FIGURE 1

<h4>Self-Rated Parameters and Health-Related Quality of Life</h4>
<p>The questionnaire was targeted on the self-evaluation of each patient at early and late follow-up. Significant changes of self-rated parameters are summarized in ( <a href="#">Table 2</a> ). According to the questionnaire, in group D significantly less patients noted an improvement of sensory deficits at late follow-up compared with early after surgery (P = 0.004; Wilcoxon signed rank test). Thus, group D developed significantly different over time compared with group S, in which sensory deficits remained stable (P = 0.034; Mann-Whitney U test). Both groups also differed significantly over time regarding motor deficits (P = 0.004; Mann-Whitney U test). Although there was no difference in improvement of motor function at early follow-up, improvement declined in group D over time, but increased in group S. As a result, after 2 years a significantly higher proportion of patients in group S rated their motor deficits being improved compared with group D (P = 0.041; Trend test).</p>
<p>Moreover, at the late time point sequestrectomy patients had significantly less pain-related drug use (P = 0.029; Trend test), as intake of pain medication greatly increased in group D between early and late follow-up (P = 0.049; Wilcoxon signed rank test). Most importantly, performance and overall outcome was also significantly better at 2-year follow-up after sequestrectomy versus microdiscectomy (performance: P = 0.054; outcome: P = 0.004; both Trend test) and was significantly improved over time only in group S (performance: P = 0.029; outcome: P = 0.021; both Wilcoxon signed rank test). Alterations in drug use and the patient's overall outcome over time is graphically illustrated in Figures 2 and 3. Favorable proportions of the Prolo score did not differ significantly between groups at the 2 time points observed, but improved significantly over time only in group S (P = 0.030; Wilcoxon signed rank test). No significant changes between groups D and S were found for the categories impairment in activities of daily living, impairment of sleep, work and sport; however, a trend was detectable in favor of the sequestrectomy group.</p>

!!! FIGURE 2
!!! FIGURE 3

<p>This positive trend 2 years after the operation could be further confirmed by the SF-36 scores. Although only the subscale vitality differed between groups at baseline, all subscales scored higher in group S at follow-up. Moreover, all SF-36 subscales of group D were below the scores of the German reference population (Figure 4).<sup>[15]</sup> The postoperative difference between groups D and S reached statistical significance for the parameters physical functioning, vitality, and social functioning (P &lt; 0.05, Mann-Whitney U test) ( <a href="#">Table 3</a> ).</p>

!!! FIGURE 4

!!! TABLE 3

<h3>Discussion</h3>

<p>The results of the first randomized study for comparison of outcome after simple microscopic sequestrectomy and standard microdiscectomy for herniated lumbar discs are presented. It has been shown that both techniques entail a comparable clinical outcome after 4 to 6 months.<sup>[6]</sup> Although these favorable results are maintained at 2 years after sequestrectomy, there is some deterioration of self-rated clinical outcome after microdiscectomy. This becomes evident by the significant superiority of sequestrectomy in important parameters like overall outcome, health-related quality-of-life (physical and social functioning, etc.), and use of analgesics. In summary, this study shows that patients after microdiscectomy show less functional capability in comparison with patients after microscopic sequestrectomy, although clinical evaluation (of nerve root symptoms) reveals no differences.</p>
<p>Microdiscectomy is being performed under the commonly accepted concept that degenerated material left in the intervertebral space (1) has a high incidence to reherniate, (2) subsequently leads to nerve root compression, and (3) is causative of clinical deterioration. As a consequence of the aforementioned assumptions, which we like to refer to as the discectomy dogma, substantial excision of disc material from the intervertebral space is often being performed. However, in our opinion each of the aforementioned statements lacks a solid scientific basis and should be discussed controversially.</p>
<p>Removal of the offending agent, i.e., the sequestrated disc material compressing the nerve root(s), is accomplished in an identical manner in sequestrectomy and microdiscectomy. Thus, if the local situation at the operated disc remains stable after surgery, symptoms of nerve root compression should rapidly subside. This improvement was dramatically present in our study and there was no difference in the clinical investigation of nerve root function between the groups. Interestingly, subjective rating of sensory and motor deficits worsened in group D over time regardless of comparable objective data. This discrepancy may be attributable to the reduced functional capabilities of these patients, which influence their rating of nerve root symptoms.</p>
<p>Does the local situation at the operated disc change like in cases of reherniations, symptoms can recur and may require further (surgical) treatment. To avoid reherniations, surgeons attempted to remove as much disc material as possible,<sup>[5]</sup> although it is well known that only partial removal is possible<sup>[16]</sup> and reoperations could obviously not be eliminated.<sup>[17]</sup> Regardless of encouraging results using the Williams' technique of less invasive disc surgery<sup>[3,4]</sup> and confirmative reports by other investigators,<sup>[5,10,11]</sup> the discectomy dogma has hardly been challenged. Except for one study,<sup>[7]</sup> however, no increase in reherniation rates has been observed with limited discectomy. We have followed this line of thought even further and completely abandoned entering the disc space. It is important to note that Williams and others have in fact entered the disc space in most of their cases, which may actually provoke reherniation by causing further damage to the annulus.<sup>[4,7]</sup></p>
<p>Reherniation rates after microdiscectomy and less invasive procedures have been discussed in more detail previously.<sup>[6]</sup> They seem to be somewhat higher in our study when compared with data from the literature. However, reherniation rates did not differ significantly between groups, so that defaulted resection of intradiscal material in group S cannot be made responsible for this discrepancy. Thus, the reason for this finding remains unclear. Possibly, uncritical diagnostic imaging and aggressive surgical retreatment at our institution in cases of recurrent symptoms may contribute to higher reherniation rates. Results of large series using a standard microdiscectomy approach report reherniation rates ranging from 3 to 6%.<sup>[17-19]</sup> However, morphologic reherniation rates, as confirmed by MRI, are largely unknown. Postdiscectomy MRI studies focused rather on early postoperative changes related to surgery than on radiological long-term results.<sup>[20,21]</sup> Recurrent disc prolapses may well be present in a substantial proportion of patients, but they may not always be associated with clinical symptoms. MRI studies in healthy volunteers indicated a relatively high incidence of disc pathologies without having any clinical significance.<sup>[22]</sup> A recently published study on MRI findings in asymptomatic individuals demonstrated that 73.2% of patients harbored protrusions and extrusions with neural compromise being detectable in 29.3%.<sup>[23]</sup></p>
<p>Reherniation resulting in nerve root compression represents only one possible cause for impaired clinical outcome after microdiscectomy. Although prospective long-term follow-up has clearly shown the initial effectiveness of disc surgery in reducing symptoms;<sup>[24]</sup> clinical outcome, however, worsens over time and merges with nonsurgical treatment after 10 years.<sup>[25]</sup> Several uncontrolled clinical and radiological studies have revealed that aggressive removal of the disc and reduction of disc height are associated with higher loads on the facet joints<sup>[26]</sup> and worse outcome.<sup>[9,27]</sup> Thus, the discectomy itself may play a crucial role in the observed clinical deterioration after surgery.</p>
<p>Pathologic changes such as facet joint degeneration, progressive endplate degeneration, loss of disc height, and lumbar instability are being increasingly recognized as important contributors to unfavorable patient outcome.<sup>[5,9,28]</sup> As these pathologic changes have been correlated with excessive resection of both, bony structures such as facet joints and soft tissue such as ligaments and degenerated disc material, operative techniques should be applied to avoid these sequelae. The approach to the spinal canal in sequestrectomy cases is less invasive in patients with caudally or cranially herniated discs, as entering the disc space is not necessary. The additional removal of bone and ligaments, however, to enter the disc space for microdiscectomy seems minimal, so that the resection of intradiscal tissue constitutes the major difference of these techniques. Removal of disc tissue is associated with a decrease in disc space height, which has been linked to segmental instability and spondylosis.<sup>[5,29]</sup> This may contribute to the later sequelae of disc surgery after asymptomatic intervals, referred to as failed-back surgery syndrome. Less aggressive discectomy has already been found to cause better radiological and clinical results.<sup>[9,27]</sup> Patients with unfavorable results of disc surgery mostly suffer from LBP rather than sciatica. Yorimitsu et al<sup>[30]</sup> reported chronic LBP in 75% of patients after 10 years, which correlated well with a decrease in disc height. However, so far no data have been retrieved from controlled studies comparing surgical techniques with different extents of disc removal. In the present study, LBP also constitutes the major postoperative clinical symptom, so that LBP seems responsible for the self-rated limitations of function and factors like analgesics usage in our microdiscectomy patients. This would support the hypothesis of accelerated segmental degeneration after removal of discal tissue. The results of our randomized study suggest that surgeons should simply leave potentially healthy disc tissue in the intervertebral space in the first place. Radiological follow-up may further elicit these relationships (see Part 2).</p>
<p>Nevertheless, 2-year follow-up seems insufficient to assess long-term fate of segmental degeneration, which constitutes a limitation of our study. According to Davis<sup>[17]</sup> a 10-year follow-up time is required to adequately measure outcome and reherniation rates. However, if accelerated degeneration or symptoms thereof can already be found after 2 years, it seems highly probable that these differences versus sequestrectomy may rather potentiate with time than decline. Another limitation of our study can be seen in the relatively small study population. Although a power analysis was performed before the study, the authors do recommend further studies to confirm the presented findings.</p>

<h3>Conclusion</h3>

<p>Reherniation rates and parameters of clinical investigation did not differ within 2 years after sequestrectomy and microdiscectomy. However, sequestrectomy was associated with better functional outcome, whereas microdiscectomy showed deterioration of the surgical result over time. Therefore, sequestrectomy may represent an attractive alternative to standard microdiscectomy.</p>

<h3>Key Points</h3>
<ul>
   <li>This monocentric randomized prospective study compared 2-year clinical outcome after lumbar microdiscectomy versus simple microscopic sequestrectomy.

</li>
   <li>Reherniation rates and objective symptoms of nerve root compression did not differ between groups.
</li>
   <li>Functional outcome deteriorated over time after microdiscectomy, whereas it remained stable after sequestrectomy.

</li>
   <li>Sequestrectomy represent an advantageous alternative to standard microdiscectomy with superior results in important parameters like quality-of-life.

</li>
</ul>

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<h3>Two-Year Outcome After Lumbar Microdiscectomy Versus Microscopic Sequestrectomy: Part 1: Evaluation of Clinical Outcome</h3>


<p>Barth, Martin MD;* Weiss, Christel MD;<sup>â€ </sup> ThomÃ©, Claudius MD*</p>

<p>*Department of Neurosurgery, and <sup>â€ </sup>Institute for Medical Statistics, University Hospital Mannheim, Medical Faculty Mannheim of the Ruprecht-Karls-University of Heidelberg, Germany.</p>
<p>Acknowledgment date: March 29, 2007. Revision date: July 22, 2007. Acceptance date: August 6, 2007.</p>
<p>The manuscript submitted does not contain information about medical device(s)/drug(s).</p>
<p>No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.</p>
<p>Claudius ThomÃ©, MD, Department of Neurosurgery, University Hospital Mannheim, Medical Faculty Mannheim of the Ruprecht-Karls-University of Heidelberg, Theodor-Kutzer-Ufer 1-3, D-68167 Mannheim, Germany; E-mail: claudius.thome@nch.ma.uni-heidelberg.de</p>




<h3>Abstract and Introduction</h3>

<h4>Abstract</h4>
<p>
   Study Design: Single-center randomized prospective study at a university hospital.

   Objective: The aim of the present study was to provide a 2-year outcome comparison of microdiscectomy (D) versus microscopic sequestrectomy (S) in terms of reherniation rates, clinical investigation, and self-rated parameters using a comprehensive questionnaire.

   Summary of Background Data: Simple fragment excision in cases of herniated lumbar discs has been repeatedly reported as an alternative to standard microdiscectomy, but prospective data with sufficient follow-up is lacking to date. Preliminary results of a prospective randomized study in patients with lumbar disc herniations indicated equal reherniation rates and a trend toward superior clinical results in patients undergoing only sequestrectomy after 4 to 6 months.

   Material and Methods: Eighty-four patients with lumbar disc herniations were treated with microdiscectomy or microscopic sequestrectomy in equal parts. Patients were re-evaluated thoroughly clinically after 2 years. Results of this investigation (low back pain, sciatica, motor-, sensory-, reflex-, straight leg raising test-indexes) and self-rated parameters including SF-36 were analyzed for differences between groups and between time points.

   Results: Thirty-eight (D) and 40 (S) patients were attainable for follow-up. Reherniation rates did not differ significantly (10.5%, group D; 12.5%, group S; P = 1.0). Following dramatic improvement after surgery in both groups, results of the clinical investigation remained stable over time without significant differences between groups. In contrast, self-rated assessment demonstrated clinical deterioration of the surgical results within the first 2 years after microdiscectomy, while they rather improved after sequestrectomy. Because of this development, the outcome measures at 2 years pointed in favor of sequestrectomy with results being significant for important parameters such as use of analgesics, performance, and overall outcome.

   Conclusion Reherniation rates within 2 years after sequestrectomy and microdiscectomy are comparable. However, outcome after microdiscectomy seems to worsen over time, whereas it remains stable after sequestrectomy. Thus, 2-year follow-up revealed clinical results favoring sequestrectomy. Performing sequestrectomy alone may therefore represent an advantageous alternative to standard microdiscectomy.

</p>

<h4>Introduction</h4>
<p>Lumbar disc herniation represents a common medical problem with numerous procedures being carried out in patients with intractable pain or severe neurological symptoms related to nerve root compression. Despite various techniques that have been developed for this indication, most patients still undergo the standard microdiscectomy as introduced by Yasargil or Caspar in 1977 using the interlaminar approach with partial resection of bony structures, the facet joints, and the ligamentum flavum followed by removal of intervertebral disc material.<sup>[1,2]</sup> This procedure has been modified to a more minimalist approach with minimal removal of bony and ligamentous structures.<sup>[3]</sup> In addition, in case of free herniated disc material it has been proposed to remove only the free fragments and tissue which can be easily mobilized from the intervertebral space. Since the introduction of this approach in 1978, several clinical studies have shown promising results without an increased incidence of reherniations.<sup>[4,5]</sup></p>
<p>In our previously published study, we prospectively compared microscopic sequestrectomy with microdiscectomy and found a comparable outcome of both approaches regarding pain and patient satisfaction after 4 to 6 months.<sup>[6]</sup> In contrast to previous studies, however, we not only included patients harboring freely herniated disc material but also patients with subligamentary and transannular herniations, thus augmenting the role of sequestrectomy. Although an increase in reherniations after simple sequestrectomy has dogmatically been brought up by the opponents of this approach,<sup>[7]</sup> other investigators have linked aggressive discectomy with accelerated segmental degeneration<sup>[8,9]</sup> and this may contribute to failed-back surgery syndrome after lumbar microdiscectomy.<sup>[5,10,11]</sup> Although reherniations are thought to occur in the early postoperative period,<sup>[4,7]</sup> further degeneration is expected thereafter. Thus, if removal of discal tissue has an impact on segmental degeneration, this should become more evident over time after microdiscectomy. On the other hand, late reherniations could cause a clinical deterioration after sequestrectomy.</p>
<p>The aim of the present follow-up study was therefore to investigate the further clinical course of either surgical groups and to statistically analyze the data not only between groups but also between time points to detect potential clinical deterioration.</p>

<h3>Clinical Materials and Methods</h3>

<h4>Study Population and Management</h4>
<p>This study is a follow-up study within the context of our previously published work<sup>[6]</sup> and has been approved by the local ethics committee. All patients from the initial study population, who had been surgically treated for a single-level lumbar disc herniation, were included. Patient inclusion criteria have been described previously. In brief, patients had to fulfill the following criteria: (1) virgin spines; (2) no emergency operation; (3) age above 18 and below 60; (4) sufficient knowledge of the German language to complete the questionnaires; (5) MRI-confirmed disc herniation; and (6) absence of concomitant spinal disease. In contrast to previous studies<sup>[3,5]</sup> not only cases with free fragments, but also subligamentary herniations and those still in continuity with the disc space (transannular herniations) were included.<sup>[6]</sup> After being randomized, patients received either a standard discectomy with removal of herniated material plus discal tissue from the intervertebral space (D) or a sequestrectomy with removal of the herniated material only (S). Unlike Williams, who removed tissue easy to mobilize from the intervertebral space,<sup>[3,4]</sup> the disc space was never entered in group S. In the case of transannular herniations where part of the fragment is still within the interspace, the fragment was grasped outside the interspace and removed in one piece without additionally entering the intervertebral space regardless of nucleus material visible in the disc space or a resulting large annular defect.</p>
<p>The procedures were performed by 2 surgeons who conducted both techniques in a standardized manner using an operating microscope (Carl Zeiss Co., Oberkochen, Germany). Discectomy included entering the disc space with a pituitary rongeur in an attempt to remove as much of the nucleus, i.e., the loose intradiscal tissue, as possible. Injury to the endplates and the annulus, however, was avoided, so that no curettes or other instruments were applied intradiscally. Thus, the central nucleectomy represents the actual difference between the procedures.</p>

<h4>Assessment of Outcome</h4>
<p>The number and dates of reherniations were documented for each group from all patients attainable via telephone interview or follow-up visit. Clinical outcome was assessed via follow-up visits. Latest follow-up was conducted 2 years after surgery. Patients who refused to participate in follow-up visits or who were lost to follow-up were excluded from the analysis of clinical parameters. Reoperations were performed in cases of symptomatic reherniations, and these patients were included in the clinical follow-up evaluation.</p>
<p>In the course of a follow-up visit each patient underwent (1) a clinical neurological investigation focusing on the lower limbs. It consisted of (A) the strength of the most affected muscle, which was graded with a range from 0 (no contraction) to 5 (full strength) and (B) the sensory index that graded sensory dysfunction in 1 (normal), 2 (slight deficit), or 3 (severe deficit). Furthermore, (C) the straight leg raising test (SLR) was assessed as 1 (61-90Â°; negative), 2 (41-60Â°; moderately positive), or 3 (0-40Â°; positive). Finally, (D) the reflex index (RI) was determined. The grading results of 3 different reflexes (adductor-, patellar-, and ankle-jerk reflex) with 1 (absent), 2 (weaker as contralateral), and 3 (normal) are summed up and divided with 3 according to the formula [(Î£ reflexes 1-3)/3] with a maximum value of 3.</p>
<p>In addition to the clinical investigation, all patients completed an extensive standardized questionnaire in which they were asked (2) to rate pain intensity for the lower back and the leg(s) during the last 5 days according the visual analog scale ranging from 0 to 10; (3) to document relieve of symptoms compared with preoperative (sensory deficit, motor deficit). The grading for each symptom ranged from 1 (much better) to 5 (much worse). To get a general idea to what extent patients are still affected, they documented (4) impairment in activities of daily living, impairment of sleep, work, or sport, physician consultations, and the extent of pain-related drug use. For analysis, answers were again graded ( <a href="#">Table 2</a> ). Additionally, the (5) performance (1 = much better to 4 = worse) and the (6) overall outcome (1 = much better to 4 = worse) were rated. Patient satisfaction was assessed using the (7) patient satisfaction index,<sup>[12,13]</sup> graded from 1 (surgery met my expectations) to 4 (I am the same or worse as compared to before surgery). Functional and economic status was investigated using (8) the Prolo score.<sup>[14]</sup> Finally, (9) health-related quality-of-life was assessed using the MOS-36 item short form health survey (SF-36).</p>

!!! TABLE 2

<h4>Statistical Analysis</h4>
<p>Before the start of the study a power analysis was performed. For simplification, the 4-scale primary outcome measures (overall outcome, performance) were interpreted as quantitative data and a difference of 0.5 points between groups was defined as clinically relevant. Considering the standard deviation derived from previous follow-up data after disc surgery, 31 patients would be required to detect this difference with 80% power at the 0.05 level. To take into account that the outcome data are ordinal and not quantitative, patient recruitment was aimed at 40 patients.</p>
<p>The Fisher exact test was used to compare patient characteristics. For the parameters LBP, sciatica, motor and sensory function, SLR, and reflex index intergroup differences at 3 time points [preoperative, early (4-6 months), and late (24 months) follow-up] were evaluated using the Cochran-Armitage Trend Test. Time-dependent changes within each group were assessed using the Wilcoxon signed rank test. To adjust for confounding factors a logistic regression using a multiple model with ordered categories was performed (alpha level = 0.10; SAS software, release 8.02; SAS Institute Inc., Cary). Wald's test was used to test which variables, like patient's gender or surgeon, had a statistically significant influence on outcome. To enable the comparison of the SF-36 results across the entire SF-36 profile with the German reference population, aged 45 to 65 years,<sup>[15]</sup> percentage changes of the mean values of both study groups to the reference population were calculated. Statistical significance was set at a probability value of less than 0.05.</p>

<h3>Results</h3>

<h4>Patient Characteristics</h4>
<p>Of 42 initially randomized patients for each group, 38 of group D and 40 of group S were attainable via telephone or personally during follow-up visits (78 in total; 93%). From these patients, 10.5% after discectomy and 12.5% after sequestrectomy suffered reherniations at levels as indicated in ( <a href="#">Table 1</a> ) (NS). Seventy-three patients sufficiently complied with the standardized clinical investigation and adequately answered the questionnaires. Follow-up time of these patients ranged from 18 to 29 months. Patient characteristics did not differ significantly and are summarized in ( <a href="#">Table 1</a> ).</p>

!!! TABLE 1

<p>Ordinal logistic regression did reveal that preoperative low back pain (LBP) was influenced by gender (P = 0.026). Postoperative scores and outcome variables were not found to be influenced by confounding factors.</p>

<h4>Pain</h4>
<p>LBP after 2 years was reduced to 2.9 Â± 2.6 in group D and to 1.8 Â± 1.9 in group S, whereas sciatica almost diminished to 1.6 Â± 2.4 (D) and to 1.2 Â± 1.8 (S). Viewing all time points separately (before surgery, early, and late follow-up), there were no significant differences between groups D and S regarding the intensity of LBP and sciatica (P > 0.05; Trend test). Compared with before surgery, both study groups experienced significant pain relief at the 2 postoperative visits for LBP and for sciatica (P < 0.0001; Wilcoxon signed rank test). Comparing both postoperative visits, no significant changes occurred in both groups regarding LBP or sciatica (group D: P = 0.243, LBP; P = 0.815, sciatica; group S: P = 0.562, LBP; P = 0.517, sciatica; Wilcoxon signed rank test).</p>

<h4>Clinical Investigation</h4>
<p>Motor grades (MG), sensory-index (SI), SLR, and RI showed positive courses with rapid postoperative improvement for both groups (Figure 1). All parameters revealed no significant intergroup differences at corresponding time points (all P-values â‰¥ 0.278; Trend test). Apart from the RI all indexes were improved significantly at early follow-up and remained significantly improved compared with preoperative levels. In the late postoperative course, i.e., between the first and the second follow-up, no significant changes were detectable for all parameters within each group (group D: P = 0.688, MG; P = 0.508, SI; P = 0.375, SLR; P = 0.774, RI; group S: P = 0.062, MG; P = 1.000, SI; P = 0.469, SLR; P = 0.234, RI; Wilcoxon signed rank test) and between both groups (P = 0.053, MG; P = 0.309, SI; P = 0.870, SLR; P = 0.529, RI; Trend test).</p>

!!! FIGURE 1

<h4>Self-Rated Parameters and Health-Related Quality of Life</h4>
<p>The questionnaire was targeted on the self-evaluation of each patient at early and late follow-up. Significant changes of self-rated parameters are summarized in ( <a href="#">Table 2</a> ). According to the questionnaire, in group D significantly less patients noted an improvement of sensory deficits at late follow-up compared with early after surgery (P = 0.004; Wilcoxon signed rank test). Thus, group D developed significantly different over time compared with group S, in which sensory deficits remained stable (P = 0.034; Mann-Whitney U test). Both groups also differed significantly over time regarding motor deficits (P = 0.004; Mann-Whitney U test). Although there was no difference in improvement of motor function at early follow-up, improvement declined in group D over time, but increased in group S. As a result, after 2 years a significantly higher proportion of patients in group S rated their motor deficits being improved compared with group D (P = 0.041; Trend test).</p>
<p>Moreover, at the late time point sequestrectomy patients had significantly less pain-related drug use (P = 0.029; Trend test), as intake of pain medication greatly increased in group D between early and late follow-up (P = 0.049; Wilcoxon signed rank test). Most importantly, performance and overall outcome was also significantly better at 2-year follow-up after sequestrectomy versus microdiscectomy (performance: P = 0.054; outcome: P = 0.004; both Trend test) and was significantly improved over time only in group S (performance: P = 0.029; outcome: P = 0.021; both Wilcoxon signed rank test). Alterations in drug use and the patient's overall outcome over time is graphically illustrated in Figures 2 and 3. Favorable proportions of the Prolo score did not differ significantly between groups at the 2 time points observed, but improved significantly over time only in group S (P = 0.030; Wilcoxon signed rank test). No significant changes between groups D and S were found for the categories impairment in activities of daily living, impairment of sleep, work and sport; however, a trend was detectable in favor of the sequestrectomy group.</p>

!!! FIGURE 2
!!! FIGURE 3

<p>This positive trend 2 years after the operation could be further confirmed by the SF-36 scores. Although only the subscale vitality differed between groups at baseline, all subscales scored higher in group S at follow-up. Moreover, all SF-36 subscales of group D were below the scores of the German reference population (Figure 4).<sup>[15]</sup> The postoperative difference between groups D and S reached statistical significance for the parameters physical functioning, vitality, and social functioning (P < 0.05, Mann-Whitney U test) ( <a href="#">Table 3</a> ).</p>

!!! FIGURE 4

!!! TABLE 3

<h3>Discussion</h3>

<p>The results of the first randomized study for comparison of outcome after simple microscopic sequestrectomy and standard microdiscectomy for herniated lumbar discs are presented. It has been shown that both techniques entail a comparable clinical outcome after 4 to 6 months.<sup>[6]</sup> Although these favorable results are maintained at 2 years after sequestrectomy, there is some deterioration of self-rated clinical outcome after microdiscectomy. This becomes evident by the significant superiority of sequestrectomy in important parameters like overall outcome, health-related quality-of-life (physical and social functioning, etc.), and use of analgesics. In summary, this study shows that patients after microdiscectomy show less functional capability in comparison with patients after microscopic sequestrectomy, although clinical evaluation (of nerve root symptoms) reveals no differences.</p>
<p>Microdiscectomy is being performed under the commonly accepted concept that degenerated material left in the intervertebral space (1) has a high incidence to reherniate, (2) subsequently leads to nerve root compression, and (3) is causative of clinical deterioration. As a consequence of the aforementioned assumptions, which we like to refer to as the discectomy dogma, substantial excision of disc material from the intervertebral space is often being performed. However, in our opinion each of the aforementioned statements lacks a solid scientific basis and should be discussed controversially.</p>
<p>Removal of the offending agent, i.e., the sequestrated disc material compressing the nerve root(s), is accomplished in an identical manner in sequestrectomy and microdiscectomy. Thus, if the local situation at the operated disc remains stable after surgery, symptoms of nerve root compression should rapidly subside. This improvement was dramatically present in our study and there was no difference in the clinical investigation of nerve root function between the groups. Interestingly, subjective rating of sensory and motor deficits worsened in group D over time regardless of comparable objective data. This discrepancy may be attributable to the reduced functional capabilities of these patients, which influence their rating of nerve root symptoms.</p>
<p>Does the local situation at the operated disc change like in cases of reherniations, symptoms can recur and may require further (surgical) treatment. To avoid reherniations, surgeons attempted to remove as much disc material as possible,<sup>[5]</sup> although it is well known that only partial removal is possible<sup>[16]</sup> and reoperations could obviously not be eliminated.<sup>[17]</sup> Regardless of encouraging results using the Williams' technique of less invasive disc surgery<sup>[3,4]</sup> and confirmative reports by other investigators,<sup>[5,10,11]</sup> the discectomy dogma has hardly been challenged. Except for one study,<sup>[7]</sup> however, no increase in reherniation rates has been observed with limited discectomy. We have followed this line of thought even further and completely abandoned entering the disc space. It is important to note that Williams and others have in fact entered the disc space in most of their cases, which may actually provoke reherniation by causing further damage to the annulus.<sup>[4,7]</sup></p>
<p>Reherniation rates after microdiscectomy and less invasive procedures have been discussed in more detail previously.<sup>[6]</sup> They seem to be somewhat higher in our study when compared with data from the literature. However, reherniation rates did not differ significantly between groups, so that defaulted resection of intradiscal material in group S cannot be made responsible for this discrepancy. Thus, the reason for this finding remains unclear. Possibly, uncritical diagnostic imaging and aggressive surgical retreatment at our institution in cases of recurrent symptoms may contribute to higher reherniation rates. Results of large series using a standard microdiscectomy approach report reherniation rates ranging from 3 to 6%.<sup>[17-19]</sup> However, morphologic reherniation rates, as confirmed by MRI, are largely unknown. Postdiscectomy MRI studies focused rather on early postoperative changes related to surgery than on radiological long-term results.<sup>[20,21]</sup> Recurrent disc prolapses may well be present in a substantial proportion of patients, but they may not always be associated with clinical symptoms. MRI studies in healthy volunteers indicated a relatively high incidence of disc pathologies without having any clinical significance.<sup>[22]</sup> A recently published study on MRI findings in asymptomatic individuals demonstrated that 73.2% of patients harbored protrusions and extrusions with neural compromise being detectable in 29.3%.<sup>[23]</sup></p>
<p>Reherniation resulting in nerve root compression represents only one possible cause for impaired clinical outcome after microdiscectomy. Although prospective long-term follow-up has clearly shown the initial effectiveness of disc surgery in reducing symptoms;<sup>[24]</sup> clinical outcome, however, worsens over time and merges with nonsurgical treatment after 10 years.<sup>[25]</sup> Several uncontrolled clinical and radiological studies have revealed that aggressive removal of the disc and reduction of disc height are associated with higher loads on the facet joints<sup>[26]</sup> and worse outcome.<sup>[9,27]</sup> Thus, the discectomy itself may play a crucial role in the observed clinical deterioration after surgery.</p>
<p>Pathologic changes such as facet joint degeneration, progressive endplate degeneration, loss of disc height, and lumbar instability are being increasingly recognized as important contributors to unfavorable patient outcome.<sup>[5,9,28]</sup> As these pathologic changes have been correlated with excessive resection of both, bony structures such as facet joints and soft tissue such as ligaments and degenerated disc material, operative techniques should be applied to avoid these sequelae. The approach to the spinal canal in sequestrectomy cases is less invasive in patients with caudally or cranially herniated discs, as entering the disc space is not necessary. The additional removal of bone and ligaments, however, to enter the disc space for microdiscectomy seems minimal, so that the resection of intradiscal tissue constitutes the major difference of these techniques. Removal of disc tissue is associated with a decrease in disc space height, which has been linked to segmental instability and spondylosis.<sup>[5,29]</sup> This may contribute to the later sequelae of disc surgery after asymptomatic intervals, referred to as failed-back surgery syndrome. Less aggressive discectomy has already been found to cause better radiological and clinical results.<sup>[9,27]</sup> Patients with unfavorable results of disc surgery mostly suffer from LBP rather than sciatica. Yorimitsu et al<sup>[30]</sup> reported chronic LBP in 75% of patients after 10 years, which correlated well with a decrease in disc height. However, so far no data have been retrieved from controlled studies comparing surgical techniques with different extents of disc removal. In the present study, LBP also constitutes the major postoperative clinical symptom, so that LBP seems responsible for the self-rated limitations of function and factors like analgesics usage in our microdiscectomy patients. This would support the hypothesis of accelerated segmental degeneration after removal of discal tissue. The results of our randomized study suggest that surgeons should simply leave potentially healthy disc tissue in the intervertebral space in the first place. Radiological follow-up may further elicit these relationships (see Part 2).</p>
<p>Nevertheless, 2-year follow-up seems insufficient to assess long-term fate of segmental degeneration, which constitutes a limitation of our study. According to Davis<sup>[17]</sup> a 10-year follow-up time is required to adequately measure outcome and reherniation rates. However, if accelerated degeneration or symptoms thereof can already be found after 2 years, it seems highly probable that these differences versus sequestrectomy may rather potentiate with time than decline. Another limitation of our study can be seen in the relatively small study population. Although a power analysis was performed before the study, the authors do recommend further studies to confirm the presented findings.</p>

<h3>Conclusion</h3>

<p>Reherniation rates and parameters of clinical investigation did not differ within 2 years after sequestrectomy and microdiscectomy. However, sequestrectomy was associated with better functional outcome, whereas microdiscectomy showed deterioration of the surgical result over time. Therefore, sequestrectomy may represent an attractive alternative to standard microdiscectomy.</p>

<h3>Key Points</h3>
<ul>
   <li>This monocentric randomized prospective study compared 2-year clinical outcome after lumbar microdiscectomy versus simple microscopic sequestrectomy.

</li>
   <li>Reherniation rates and objective symptoms of nerve root compression did not differ between groups.
</li>
   <li>Functional outcome deteriorated over time after microdiscectomy, whereas it remained stable after sequestrectomy.

</li>
   <li>Sequestrectomy represent an advantageous alternative to standard microdiscectomy with superior results in important parameters like quality-of-life.

</li>
</ul>

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</ol>

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<h3>Two-Year Outcome After Lumbar Microdiscectomy Versus Microscopic Sequestrectomy: Part 1: Evaluation of Clinical Outcome</h3>


<p>Barth, Martin MD;* Weiss, Christel MD;<sup>â€ </sup> ThomÃ©, Claudius MD*</p>

<p>*Department of Neurosurgery, and <sup>â€ </sup>Institute for Medical Statistics, University Hospital Mannheim, Medical Faculty Mannheim of the Ruprecht-Karls-University of Heidelberg, Germany.</p>
<p>Acknowledgment date: March 29, 2007. Revision date: July 22, 2007. Acceptance date: August 6, 2007.</p>
<p>The manuscript submitted does not contain information about medical device(s)/drug(s).</p>
<p>No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.</p>
<p>Claudius ThomÃ©, MD, Department of Neurosurgery, University Hospital Mannheim, Medical Faculty Mannheim of the Ruprecht-Karls-University of Heidelberg, Theodor-Kutzer-Ufer 1-3, D-68167 Mannheim, Germany; E-mail: claudius.thome@nch.ma.uni-heidelberg.de</p>




<h3>Abstract and Introduction</h3>

<h4>Abstract</h4>
<p>
   Study Design: Single-center randomized prospective study at a university hospital.

   Objective: The aim of the present study was to provide a 2-year outcome comparison of microdiscectomy (D) versus microscopic sequestrectomy (S) in terms of reherniation rates, clinical investigation, and self-rated parameters using a comprehensive questionnaire.

   Summary of Background Data: Simple fragment excision in cases of herniated lumbar discs has been repeatedly reported as an alternative to standard microdiscectomy, but prospective data with sufficient follow-up is lacking to date. Preliminary results of a prospective randomized study in patients with lumbar disc herniations indicated equal reherniation rates and a trend toward superior clinical results in patients undergoing only sequestrectomy after 4 to 6 months.

   Material and Methods: Eighty-four patients with lumbar disc herniations were treated with microdiscectomy or microscopic sequestrectomy in equal parts. Patients were re-evaluated thoroughly clinically after 2 years. Results of this investigation (low back pain, sciatica, motor-, sensory-, reflex-, straight leg raising test-indexes) and self-rated parameters including SF-36 were analyzed for differences between groups and between time points.

   Results: Thirty-eight (D) and 40 (S) patients were attainable for follow-up. Reherniation rates did not differ significantly (10.5%, group D; 12.5%, group S; P = 1.0). Following dramatic improvement after surgery in both groups, results of the clinical investigation remained stable over time without significant differences between groups. In contrast, self-rated assessment demonstrated clinical deterioration of the surgical results within the first 2 years after microdiscectomy, while they rather improved after sequestrectomy. Because of this development, the outcome measures at 2 years pointed in favor of sequestrectomy with results being significant for important parameters such as use of analgesics, performance, and overall outcome.

   Conclusion Reherniation rates within 2 years after sequestrectomy and microdiscectomy are comparable. However, outcome after microdiscectomy seems to worsen over time, whereas it remains stable after sequestrectomy. Thus, 2-year follow-up revealed clinical results favoring sequestrectomy. Performing sequestrectomy alone may therefore represent an advantageous alternative to standard microdiscectomy.

</p>

<h4>Introduction</h4>
<p>Lumbar disc herniation represents a common medical problem with numerous procedures being carried out in patients with intractable pain or severe neurological symptoms related to nerve root compression. Despite various techniques that have been developed for this indication, most patients still undergo the standard microdiscectomy as introduced by Yasargil or Caspar in 1977 using the interlaminar approach with partial resection of bony structures, the facet joints, and the ligamentum flavum followed by removal of intervertebral disc material.<sup>[1,2]</sup> This procedure has been modified to a more minimalist approach with minimal removal of bony and ligamentous structures.<sup>[3]</sup> In addition, in case of free herniated disc material it has been proposed to remove only the free fragments and tissue which can be easily mobilized from the intervertebral space. Since the introduction of this approach in 1978, several clinical studies have shown promising results without an increased incidence of reherniations.<sup>[4,5]</sup></p>
<p>In our previously published study, we prospectively compared microscopic sequestrectomy with microdiscectomy and found a comparable outcome of both approaches regarding pain and patient satisfaction after 4 to 6 months.<sup>[6]</sup> In contrast to previous studies, however, we not only included patients harboring freely herniated disc material but also patients with subligamentary and transannular herniations, thus augmenting the role of sequestrectomy. Although an increase in reherniations after simple sequestrectomy has dogmatically been brought up by the opponents of this approach,<sup>[7]</sup> other investigators have linked aggressive discectomy with accelerated segmental degeneration<sup>[8,9]</sup> and this may contribute to failed-back surgery syndrome after lumbar microdiscectomy.<sup>[5,10,11]</sup> Although reherniations are thought to occur in the early postoperative period,<sup>[4,7]</sup> further degeneration is expected thereafter. Thus, if removal of discal tissue has an impact on segmental degeneration, this should become more evident over time after microdiscectomy. On the other hand, late reherniations could cause a clinical deterioration after sequestrectomy.</p>
<p>The aim of the present follow-up study was therefore to investigate the further clinical course of either surgical groups and to statistically analyze the data not only between groups but also between time points to detect potential clinical deterioration.</p>

<h3>Clinical Materials and Methods</h3>

<h4>Study Population and Management</h4>
<p>This study is a follow-up study within the context of our previously published work<sup>[6]</sup> and has been approved by the local ethics committee. All patients from the initial study population, who had been surgically treated for a single-level lumbar disc herniation, were included. Patient inclusion criteria have been described previously. In brief, patients had to fulfill the following criteria: (1) virgin spines; (2) no emergency operation; (3) age above 18 and below 60; (4) sufficient knowledge of the German language to complete the questionnaires; (5) MRI-confirmed disc herniation; and (6) absence of concomitant spinal disease. In contrast to previous studies<sup>[3,5]</sup> not only cases with free fragments, but also subligamentary herniations and those still in continuity with the disc space (transannular herniations) were included.<sup>[6]</sup> After being randomized, patients received either a standard discectomy with removal of herniated material plus discal tissue from the intervertebral space (D) or a sequestrectomy with removal of the herniated material only (S). Unlike Williams, who removed tissue easy to mobilize from the intervertebral space,<sup>[3,4]</sup> the disc space was never entered in group S. In the case of transannular herniations where part of the fragment is still within the interspace, the fragment was grasped outside the interspace and removed in one piece without additionally entering the intervertebral space regardless of nucleus material visible in the disc space or a resulting large annular defect.</p>
<p>The procedures were performed by 2 surgeons who conducted both techniques in a standardized manner using an operating microscope (Carl Zeiss Co., Oberkochen, Germany). Discectomy included entering the disc space with a pituitary rongeur in an attempt to remove as much of the nucleus, i.e., the loose intradiscal tissue, as possible. Injury to the endplates and the annulus, however, was avoided, so that no curettes or other instruments were applied intradiscally. Thus, the central nucleectomy represents the actual difference between the procedures.</p>

<h4>Assessment of Outcome</h4>
<p>The number and dates of reherniations were documented for each group from all patients attainable via telephone interview or follow-up visit. Clinical outcome was assessed via follow-up visits. Latest follow-up was conducted 2 years after surgery. Patients who refused to participate in follow-up visits or who were lost to follow-up were excluded from the analysis of clinical parameters. Reoperations were performed in cases of symptomatic reherniations, and these patients were included in the clinical follow-up evaluation.</p>
<p>In the course of a follow-up visit each patient underwent (1) a clinical neurological investigation focusing on the lower limbs. It consisted of (A) the strength of the most affected muscle, which was graded with a range from 0 (no contraction) to 5 (full strength) and (B) the sensory index that graded sensory dysfunction in 1 (normal), 2 (slight deficit), or 3 (severe deficit). Furthermore, (C) the straight leg raising test (SLR) was assessed as 1 (61-90Â°; negative), 2 (41-60Â°; moderately positive), or 3 (0-40Â°; positive). Finally, (D) the reflex index (RI) was determined. The grading results of 3 different reflexes (adductor-, patellar-, and ankle-jerk reflex) with 1 (absent), 2 (weaker as contralateral), and 3 (normal) are summed up and divided with 3 according to the formula [(Î£ reflexes 1-3)/3] with a maximum value of 3.</p>
<p>In addition to the clinical investigation, all patients completed an extensive standardized questionnaire in which they were asked (2) to rate pain intensity for the lower back and the leg(s) during the last 5 days according the visual analog scale ranging from 0 to 10; (3) to document relieve of symptoms compared with preoperative (sensory deficit, motor deficit). The grading for each symptom ranged from 1 (much better) to 5 (much worse). To get a general idea to what extent patients are still affected, they documented (4) impairment in activities of daily living, impairment of sleep, work, or sport, physician consultations, and the extent of pain-related drug use. For analysis, answers were again graded ( <a href="#">Table 2</a> ). Additionally, the (5) performance (1 = much better to 4 = worse) and the (6) overall outcome (1 = much better to 4 = worse) were rated. Patient satisfaction was assessed using the (7) patient satisfaction index,<sup>[12,13]</sup> graded from 1 (surgery met my expectations) to 4 (I am the same or worse as compared to before surgery). Functional and economic status was investigated using (8) the Prolo score.<sup>[14]</sup> Finally, (9) health-related quality-of-life was assessed using the MOS-36 item short form health survey (SF-36).</p>

!!! TABLE 2

<h4>Statistical Analysis</h4>
<p>Before the start of the study a power analysis was performed. For simplification, the 4-scale primary outcome measures (overall outcome, performance) were interpreted as quantitative data and a difference of 0.5 points between groups was defined as clinically relevant. Considering the standard deviation derived from previous follow-up data after disc surgery, 31 patients would be required to detect this difference with 80% power at the 0.05 level. To take into account that the outcome data are ordinal and not quantitative, patient recruitment was aimed at 40 patients.</p>
<p>The Fisher exact test was used to compare patient characteristics. For the parameters LBP, sciatica, motor and sensory function, SLR, and reflex index intergroup differences at 3 time points [preoperative, early (4-6 months), and late (24 months) follow-up] were evaluated using the Cochran-Armitage Trend Test. Time-dependent changes within each group were assessed using the Wilcoxon signed rank test. To adjust for confounding factors a logistic regression using a multiple model with ordered categories was performed (alpha level = 0.10; SAS software, release 8.02; SAS Institute Inc., Cary). Wald's test was used to test which variables, like patient's gender or surgeon, had a statistically significant influence on outcome. To enable the comparison of the SF-36 results across the entire SF-36 profile with the German reference population, aged 45 to 65 years,<sup>[15]</sup> percentage changes of the mean values of both study groups to the reference population were calculated. Statistical significance was set at a probability value of less than 0.05.</p>

<h3>Results</h3>

<h4>Patient Characteristics</h4>
<p>Of 42 initially randomized patients for each group, 38 of group D and 40 of group S were attainable via telephone or personally during follow-up visits (78 in total; 93%). From these patients, 10.5% after discectomy and 12.5% after sequestrectomy suffered reherniations at levels as indicated in ( <a href="#">Table 1</a> ) (NS). Seventy-three patients sufficiently complied with the standardized clinical investigation and adequately answered the questionnaires. Follow-up time of these patients ranged from 18 to 29 months. Patient characteristics did not differ significantly and are summarized in ( <a href="#">Table 1</a> ).</p>

!!! TABLE 1

<p>Ordinal logistic regression did reveal that preoperative low back pain (LBP) was influenced by gender (P = 0.026). Postoperative scores and outcome variables were not found to be influenced by confounding factors.</p>

<h4>Pain</h4>
<p>LBP after 2 years was reduced to 2.9 Â± 2.6 in group D and to 1.8 Â± 1.9 in group S, whereas sciatica almost diminished to 1.6 Â± 2.4 (D) and to 1.2 Â± 1.8 (S). Viewing all time points separately (before surgery, early, and late follow-up), there were no significant differences between groups D and S regarding the intensity of LBP and sciatica (P > 0.05; Trend test). Compared with before surgery, both study groups experienced significant pain relief at the 2 postoperative visits for LBP and for sciatica (P < 0.0001; Wilcoxon signed rank test). Comparing both postoperative visits, no significant changes occurred in both groups regarding LBP or sciatica (group D: P = 0.243, LBP; P = 0.815, sciatica; group S: P = 0.562, LBP; P = 0.517, sciatica; Wilcoxon signed rank test).</p>

<h4>Clinical Investigation</h4>
<p>Motor grades (MG), sensory-index (SI), SLR, and RI showed positive courses with rapid postoperative improvement for both groups (Figure 1). All parameters revealed no significant intergroup differences at corresponding time points (all P-values â‰¥ 0.278; Trend test). Apart from the RI all indexes were improved significantly at early follow-up and remained significantly improved compared with preoperative levels. In the late postoperative course, i.e., between the first and the second follow-up, no significant changes were detectable for all parameters within each group (group D: P = 0.688, MG; P = 0.508, SI; P = 0.375, SLR; P = 0.774, RI; group S: P = 0.062, MG; P = 1.000, SI; P = 0.469, SLR; P = 0.234, RI; Wilcoxon signed rank test) and between both groups (P = 0.053, MG; P = 0.309, SI; P = 0.870, SLR; P = 0.529, RI; Trend test).</p>

!!! FIGURE 1

<h4>Self-Rated Parameters and Health-Related Quality of Life</h4>
<p>The questionnaire was targeted on the self-evaluation of each patient at early and late follow-up. Significant changes of self-rated parameters are summarized in ( <a href="#">Table 2</a> ). According to the questionnaire, in group D significantly less patients noted an improvement of sensory deficits at late follow-up compared with early after surgery (P = 0.004; Wilcoxon signed rank test). Thus, group D developed significantly different over time compared with group S, in which sensory deficits remained stable (P = 0.034; Mann-Whitney U test). Both groups also differed significantly over time regarding motor deficits (P = 0.004; Mann-Whitney U test). Although there was no difference in improvement of motor function at early follow-up, improvement declined in group D over time, but increased in group S. As a result, after 2 years a significantly higher proportion of patients in group S rated their motor deficits being improved compared with group D (P = 0.041; Trend test).</p>
<p>Moreover, at the late time point sequestrectomy patients had significantly less pain-related drug use (P = 0.029; Trend test), as intake of pain medication greatly increased in group D between early and late follow-up (P = 0.049; Wilcoxon signed rank test). Most importantly, performance and overall outcome was also significantly better at 2-year follow-up after sequestrectomy versus microdiscectomy (performance: P = 0.054; outcome: P = 0.004; both Trend test) and was significantly improved over time only in group S (performance: P = 0.029; outcome: P = 0.021; both Wilcoxon signed rank test). Alterations in drug use and the patient's overall outcome over time is graphically illustrated in Figures 2 and 3. Favorable proportions of the Prolo score did not differ significantly between groups at the 2 time points observed, but improved significantly over time only in group S (P = 0.030; Wilcoxon signed rank test). No significant changes between groups D and S were found for the categories impairment in activities of daily living, impairment of sleep, work and sport; however, a trend was detectable in favor of the sequestrectomy group.</p>

!!! FIGURE 2
!!! FIGURE 3

<p>This positive trend 2 years after the operation could be further confirmed by the SF-36 scores. Although only the subscale vitality differed between groups at baseline, all subscales scored higher in group S at follow-up. Moreover, all SF-36 subscales of group D were below the scores of the German reference population (Figure 4).<sup>[15]</sup> The postoperative difference between groups D and S reached statistical significance for the parameters physical functioning, vitality, and social functioning (P < 0.05, Mann-Whitney U test) ( <a href="#">Table 3</a> ).</p>

!!! FIGURE 4

!!! TABLE 3

<h3>Discussion</h3>

<p>The results of the first randomized study for comparison of outcome after simple microscopic sequestrectomy and standard microdiscectomy for herniated lumbar discs are presented. It has been shown that both techniques entail a comparable clinical outcome after 4 to 6 months.<sup>[6]</sup> Although these favorable results are maintained at 2 years after sequestrectomy, there is some deterioration of self-rated clinical outcome after microdiscectomy. This becomes evident by the significant superiority of sequestrectomy in important parameters like overall outcome, health-related quality-of-life (physical and social functioning, etc.), and use of analgesics. In summary, this study shows that patients after microdiscectomy show less functional capability in comparison with patients after microscopic sequestrectomy, although clinical evaluation (of nerve root symptoms) reveals no differences.</p>
<p>Microdiscectomy is being performed under the commonly accepted concept that degenerated material left in the intervertebral space (1) has a high incidence to reherniate, (2) subsequently leads to nerve root compression, and (3) is causative of clinical deterioration. As a consequence of the aforementioned assumptions, which we like to refer to as the discectomy dogma, substantial excision of disc material from the intervertebral space is often being performed. However, in our opinion each of the aforementioned statements lacks a solid scientific basis and should be discussed controversially.</p>
<p>Removal of the offending agent, i.e., the sequestrated disc material compressing the nerve root(s), is accomplished in an identical manner in sequestrectomy and microdiscectomy. Thus, if the local situation at the operated disc remains stable after surgery, symptoms of nerve root compression should rapidly subside. This improvement was dramatically present in our study and there was no difference in the clinical investigation of nerve root function between the groups. Interestingly, subjective rating of sensory and motor deficits worsened in group D over time regardless of comparable objective data. This discrepancy may be attributable to the reduced functional capabilities of these patients, which influence their rating of nerve root symptoms.</p>
<p>Does the local situation at the operated disc change like in cases of reherniations, symptoms can recur and may require further (surgical) treatment. To avoid reherniations, surgeons attempted to remove as much disc material as possible,<sup>[5]</sup> although it is well known that only partial removal is possible<sup>[16]</sup> and reoperations could obviously not be eliminated.<sup>[17]</sup> Regardless of encouraging results using the Williams' technique of less invasive disc surgery<sup>[3,4]</sup> and confirmative reports by other investigators,<sup>[5,10,11]</sup> the discectomy dogma has hardly been challenged. Except for one study,<sup>[7]</sup> however, no increase in reherniation rates has been observed with limited discectomy. We have followed this line of thought even further and completely abandoned entering the disc space. It is important to note that Williams and others have in fact entered the disc space in most of their cases, which may actually provoke reherniation by causing further damage to the annulus.<sup>[4,7]</sup></p>
<p>Reherniation rates after microdiscectomy and less invasive procedures have been discussed in more detail previously.<sup>[6]</sup> They seem to be somewhat higher in our study when compared with data from the literature. However, reherniation rates did not differ significantly between groups, so that defaulted resection of intradiscal material in group S cannot be made responsible for this discrepancy. Thus, the reason for this finding remains unclear. Possibly, uncritical diagnostic imaging and aggressive surgical retreatment at our institution in cases of recurrent symptoms may contribute to higher reherniation rates. Results of large series using a standard microdiscectomy approach report reherniation rates ranging from 3 to 6%.<sup>[17-19]</sup> However, morphologic reherniation rates, as confirmed by MRI, are largely unknown. Postdiscectomy MRI studies focused rather on early postoperative changes related to surgery than on radiological long-term results.<sup>[20,21]</sup> Recurrent disc prolapses may well be present in a substantial proportion of patients, but they may not always be associated with clinical symptoms. MRI studies in healthy volunteers indicated a relatively high incidence of disc pathologies without having any clinical significance.<sup>[22]</sup> A recently published study on MRI findings in asymptomatic individuals demonstrated that 73.2% of patients harbored protrusions and extrusions with neural compromise being detectable in 29.3%.<sup>[23]</sup></p>
<p>Reherniation resulting in nerve root compression represents only one possible cause for impaired clinical outcome after microdiscectomy. Although prospective long-term follow-up has clearly shown the initial effectiveness of disc surgery in reducing symptoms;<sup>[24]</sup> clinical outcome, however, worsens over time and merges with nonsurgical treatment after 10 years.<sup>[25]</sup> Several uncontrolled clinical and radiological studies have revealed that aggressive removal of the disc and reduction of disc height are associated with higher loads on the facet joints<sup>[26]</sup> and worse outcome.<sup>[9,27]</sup> Thus, the discectomy itself may play a crucial role in the observed clinical deterioration after surgery.</p>
<p>Pathologic changes such as facet joint degeneration, progressive endplate degeneration, loss of disc height, and lumbar instability are being increasingly recognized as important contributors to unfavorable patient outcome.<sup>[5,9,28]</sup> As these pathologic changes have been correlated with excessive resection of both, bony structures such as facet joints and soft tissue such as ligaments and degenerated disc material, operative techniques should be applied to avoid these sequelae. The approach to the spinal canal in sequestrectomy cases is less invasive in patients with caudally or cranially herniated discs, as entering the disc space is not necessary. The additional removal of bone and ligaments, however, to enter the disc space for microdiscectomy seems minimal, so that the resection of intradiscal tissue constitutes the major difference of these techniques. Removal of disc tissue is associated with a decrease in disc space height, which has been linked to segmental instability and spondylosis.<sup>[5,29]</sup> This may contribute to the later sequelae of disc surgery after asymptomatic intervals, referred to as failed-back surgery syndrome. Less aggressive discectomy has already been found to cause better radiological and clinical results.<sup>[9,27]</sup> Patients with unfavorable results of disc surgery mostly suffer from LBP rather than sciatica. Yorimitsu et al<sup>[30]</sup> reported chronic LBP in 75% of patients after 10 years, which correlated well with a decrease in disc height. However, so far no data have been retrieved from controlled studies comparing surgical techniques with different extents of disc removal. In the present study, LBP also constitutes the major postoperative clinical symptom, so that LBP seems responsible for the self-rated limitations of function and factors like analgesics usage in our microdiscectomy patients. This would support the hypothesis of accelerated segmental degeneration after removal of discal tissue. The results of our randomized study suggest that surgeons should simply leave potentially healthy disc tissue in the intervertebral space in the first place. Radiological follow-up may further elicit these relationships (see Part 2).</p>
<p>Nevertheless, 2-year follow-up seems insufficient to assess long-term fate of segmental degeneration, which constitutes a limitation of our study. According to Davis<sup>[17]</sup> a 10-year follow-up time is required to adequately measure outcome and reherniation rates. However, if accelerated degeneration or symptoms thereof can already be found after 2 years, it seems highly probable that these differences versus sequestrectomy may rather potentiate with time than decline. Another limitation of our study can be seen in the relatively small study population. Although a power analysis was performed before the study, the authors do recommend further studies to confirm the presented findings.</p>

<h3>Conclusion</h3>

<p>Reherniation rates and parameters of clinical investigation did not differ within 2 years after sequestrectomy and microdiscectomy. However, sequestrectomy was associated with better functional outcome, whereas microdiscectomy showed deterioration of the surgical result over time. Therefore, sequestrectomy may represent an attractive alternative to standard microdiscectomy.</p>

<h3>Key Points</h3>
<ul>
   <li>This monocentric randomized prospective study compared 2-year clinical outcome after lumbar microdiscectomy versus simple microscopic sequestrectomy.

</li>
   <li>Reherniation rates and objective symptoms of nerve root compression did not differ between groups.
</li>
   <li>Functional outcome deteriorated over time after microdiscectomy, whereas it remained stable after sequestrectomy.

</li>
   <li>Sequestrectomy represent an advantageous alternative to standard microdiscectomy with superior results in important parameters like quality-of-life.

</li>
</ul>

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</ol>

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