Indirect Decompression for the Treatment of Degenerative Lumbar Stenosis

Discussion

This study found that indirect decompression via ALIF was effective in treating lumbar spinal stenosis with statistically significant improvement in back pain, leg pain, and ODI scores. Only 4% of patients later underwent direct decompression at the index level. This finding is consistent with the existing literature in which rates of subsequent direct decompression have been reported at 2% to 9.5%.11–13

In previous smaller studies, the following risk factors for failed indirect decompression have been identified: significant osteophytes (particularly those arising from the posterior end plates or significant enough to lock the facets), ossification of the posterior longitudinal ligament, preoperative motor deficit, rest pain, high scores on the Japanese Outcome Assessment questionnaire preoperatively, spondylolisthesis with greater than a moderate slip, and spondylolisthesis at L5-1 in an obese patient.10,11,13,14 Older age was the only factor investigated in the present study that was associated with failure of indirect decompression. While radiographic parameters were not directly assessed, this finding may be due to the additional spondylosis (and associated osseous stenosis) likely exhibited in older patients. It therefore follows that considering the size and location of osteophytes is reasonable in deciding whether direct decompression might be warranted as large osteophytes, unlike soft tissue, would not be expected to reduce with distraction and may tether the neural elements. Advanced age may also be a proxy for reduced bone density, and subsidence with loss of ligamentotaxis may also be implicated in the higher failure rate observed in older patients.

Contrary to the findings of Khalsa et al,10 this study did not identify an association between rest pain (as indicated by response to ODI Section 7) and rates of failure of indirect decompression. However, a number of differences exist that likely contribute to this discrepancy. Over 85% of patients in the Khalsa et al. study exhibited neurogenic claudication compared with just over 10% here. It may therefore be the case that rest pain is a better indicator for failure of indirect decompression for the treatment of central stenosis and associated neurogenic claudication than it is in the setting of radiculopathy. Furthermore, the definition of failure differed between studies with Khalsa et al considering postoperative pain scores and the present investigation utilizing return to the operating room.

While a variety of lumbar interbody fusion techniques are available, the current study focused specifically on patients undergoing ALIF rather than any other approaches. ALIF may offer advantages over other interbody techniques for performing indirect decompression. Some studies have found that ALIF is associated with significantly greater increases in foraminal height.15,16 By providing a large exposure to the disc space, ALIF allows rapid disc tissue evacuation and end plate preparation, maximal implant size and surface area, and superior segmental and overall lumbar lordosis.17,18 There are also a wide variety of cage heights and angulations to facilitate achieving the desired degree of distraction and lordosis. However, ALIF is not always a viable option, depending on vertebral level and visceral anatomy.

This study included stand-alone ALIF as well as ALIF with supplemental posterior instrumentation. There were no significant differences in the clinical outcome, failure rates of indirect decompression, or reoperation rates when comparing the ALIF vs ALIF + PI groups. This supports the notion that posterior fixation may be omitted in appropriately indicated patients without causing undue risk of reoperation or poor outcomes. Foregoing posterior instrumentation reduces operative time and implant costs, preserves the posterior tissues, and eliminates the risk of pedicle screw breaches as well as the possible need for subsequent surgery to remove painful posterior instrumentation (which occurred in 10.1% of ALIF + PI patients in the current series). Further investigation is needed to determine which cases necessitate posterior instrumentation, but it may be prudent in patients with Grade II or greater spondylolisthesis, segmental instability, deformity, or poor bone stock.

This study is not without limitations. The decision of whether direct decompression was performed at the time of the index procedure was made by the treating surgeon without a standardized algorithm, and only patients in whom indirect decompression was relied upon were followed. The retrospective, nonrandomized design of the current study was not optimal. Details of the criteria used by surgeons to decide to employ only indirect decompression or to include posterior fixation could not be determined. However, the low rate of reoperation for direct decompression suggests that the surgeons selected appropriate cases for indirect decompression in the large majority of cases. What the results cannot address is whether more patients may have been appropriate candidates for indirect decompression but received direct decompression nonetheless. Furthermore, any patients who might have done poorly and undergone subsequent direct decompression at another practice would not have been captured. This would have artificially reduced the observed failure rate. Due to the focus on ALIF, nearly three-quarters of the patients in this study underwent surgery at the L5-S1 level, primarily for radiculopathy rather than neurogenic claudication. The results presented herein are therefore most applicable to patients with these clinical characteristics. Finally, radiographic and other imaging parameters were not collected or included in the analysis. Future studies investigating the impact of particular imaging findings would add to the understanding of this topic.