Source of Support

One of the Authors is a research registrar supported by the commercial entity Zimmer (Warsaw, Indiana, USA) and is supported by a fund or grant in excess of £10,000 in one year.

Key points

Introduction

Lumbar spinal stenosis is defined as narrowing of the lumbar spinal canal resulting in entrapment and compression of intraspinal neural and vascular structures. The case for surgical decompression of the spinal canal and neural foramen is well established ₁,₂ .

There is however a trend towards more conservative bony resection in light of growing evidence that extensive bony resection may lead to spinal instability ₃,₄,₅ . Quint and co-workers performed human cadaver work to support this hypothesis.

In view of these findings, several “minimally invasive” or more accurately “less destructive” surgical techniques have been described or are in development ₆,₇,₈ . Kleeman ₆ performed a wide fenestration and undercutting medial facetectomy and reported 88% good results at 4 years in 54 patients. Weiner ₇ reported 66% satisfaction in 50 patients using the spinous process osteotomy described by Yong-Hing and Kirkaldy-Willis.

The results of surgical decompression for LSS reported in the literature have been very varied and sometimes inconsistent ₉,₁₀ . The possible reasons for this variation in good outcome include patient comorbidity and psychological factors, inadequacy of decompression and the wide variety of outcome measures that have been employed in the literature in order to define a successful surgical outcome. In this study, the patient reported satisfaction with surgery was chosen as the definition of a successful outcome. Patient reported satisfaction with intervention has been validated as an outcome measure ₁₁ and has been employed in other studies ₁₂ .

Other studies have employed general disease measures (e.g. the SF-36) and disease specific measures (e.g. Shuttle Walking test) in patient assessment. Patient satisfaction however, is arguably the most important factor to both the patient and surgeon following a surgical intervention.

Materials And Methods

The records of a consecutive series of 47 patients who presented between January 1998 and December 2001 with clinical evidence of LSS and who subsequently underwent Undercutting Laminectomy and Medial facetectomy were reviewed.

Operative levels and complications were also retrieved from the records.

Clinical Assessment

Radiological Assessment

Surgical Technique

Statistics

Results

Clinical Outcome

Complications

Radiological Outcome

Discussion

The results of surgical decompression for LSS are highly variable. Reported success rates vary from 26 to 100 % ₉ . The possible factors that may account for this variation include patient factors, surgical factors and assessment factors. Several authors have attempted to clarify the reasons for the wide variation in surgical outcomes ₁₃ . These include patient comorbidity ₁₄ and psychological factors ₁₅ .

Many studies have not taken into account such factors as patient comorbidity, expectations or psychological factors. This elderly group of patients often have cardiac, respiratory and vascular pathology that make objective assessment of outcome of LSS surgery difficult to quantify. There is considerable evidence to show that the outcome of surgery is to some extent determined but psychological factors and most studies of surgery for LSS, including this one, have not assessed these in this elderly population.

The clinical history of spinal claudicaition is readily recognised but given the general paucity of localising signs, clinicians rely greatly on preoperative imaging in order to identify the site and level of stenosis. CT myelography is regarded the “gold-standard” ₁₆ but is invasive and has been largely superseded by MRI. There are few reports in the literature in which MRI has been the definitive radiological investigation. Early reports relying solely on CT may have underestimated the degree or extent of compression. CT may underestimate the degree of compression attributable to the disc, facet joints and ligamentum flavum. Many clinicians however continue to use CT preoperatively given its wider availability and lower cost. All patients in this series had MRI follow-up. It is imperative that the site of compression be it central, lateral recess or foraminal be identified preoperatively if properly directed decompression is to be achieved.

The plethora of surgical procedures that have been used in decompression of LSS include extensive laminectomy (“Christmas-tree” procedure), “Port-hole” laminectomy ₆ , expansive laminoplasty ₁₇ , spinous process osteotomy ₇ , endoscopic laminectomy ₈ and now Undercutting Laminectomy. None of these has been shown to yield superior results and as long as complete neural decompression has been achieved one would expect to see no difference. Conventional laminectomy effectively decompresses the neural elements but may do so at the expense of spinal stability. Surgical techniques that preserve the posterior spinal elements have the theoretical advantage of maintaining spinal stability as the osseous integrity of the segment is less likely to be compromised. It is yet to be seen whether the incidence of later spondylolisthesis using these techniques is less when compared to conventional laminectomy.

There are a wide variety of instruments that have been used to assess outcome ₁₈,₁₉ . The definition of a successful outcome is therefore very variable across the literature. Disease-specific measures (like the ODI) ₂₀ and general health measures (SF-36) have been used by other authors. Functional measures (Shuttle-walking test) are compromised by the frequent comorbidity in this patient group and may not accurately reflect the neural compression element of the patient's disease. Patient satisfaction is arguably the most important outcome measure for both patient and surgeon and for this reason has been employed in this study.

Much attention has been paid to elucidating preoperative factors that may better predict those patients who respond favourably to surgical treatment. The overall impression from the literature is that there are no clear predictors of outcome from surgery. Our finding of better satisfaction with longer duration of symptoms is difficult to explain. One reason may be that the patients' subjective relief following surgery is greater the longer their duration of symptoms.

There have been published reports which demonstrate that the adequacy of decompression as judged by Computerised Tomography (CT) does not correlate with patient-reported outcome ₂₁ . This is supported by our findings using MRI as the imaging modality.

Undercutting laminectomy and Medial factectomy produces complete neural decompression and patient-reported satisfaction following the procedure was comparable to that reported in the literature using more destructive conventional techniques. No increased incidence of complications was noted. Preoperative length of symptoms has been identified as a possible predictor of surgical outcome. No other variables were found to be of predictive value. Postoperative pain and limitation of ADL does not necessarily correlate with patient satisfaction and adequate decompression as judged by MRI does not predict a satisfactory clinical outcome.

This study is limited by the small patient sample and the consequent low statistical power. No preoperative quantitative data was available to allow comparison using validated instruments but patient satisfaction is arguably the most relevant outcome measure for both surgeon and patient. The Interobserver error in assessing cross-sectional area of the spinal canal, using the method that we employed has not been assessed but is under investigation.

Undercutting laminectomy and Medial facetectomy, by preserving the posterior elements, may lessen the incidence of post-decompression spondylolisthesis but this requires further study ideally using a randomised group of patients followed-up for many years.

Greater number of patients is required to improve statistical power but this is difficult without multicentre trials.

Correspondence to

Mr. R Sharma MRCS Flat 7, 35 Collingham Place, London, England SW5 0QF Email: rsharma101@hotmail.com Mobile: 07967503397