Biomechanical comparison of lumbar spine instability between laminectomy and bilateral laminotomy for spinal stenosis syndrome - an experimental study in porcine model

Abstract

Background: The association of lumbar spine instability between laminectomy and laminotomy has been clinically studied, but the corresponding in vitro biomechanical studies have not been reported. We investigated the hypothesis that the integrity of the posterior complex (spinous process-interspinous ligament-spinous process) plays an important role on the postoperative spinal stability in decompressive surgery.

Methods: Eight porcine lumbar spine specimens were studied. Each specimen was tested intact and after two decompression procedures. All posterior components were preserved in Group A (Intact). In Group B (Bilateral laminotomy), the inferior margin of L4 lamina and superior margin of L5 lamina were removed, but the L4-L5 supraspinous ligament was preserved. Fenestrations were made on both sides. In Group C (Laminectomy) the lamina and spinous processes of lower L4 and upper L5 were removed. Ligamentum flavum and supraspinous ligament of L4-L5 were removed. A hydraulic testing machine was used to generate an increasing moment up to 8400 N-mm in flexion and extension. Intervertebral displacement at decompressive level L4-L5 was measured by extensometer

Results: The results indicated that, under extension motion, intervertebral displacement between the specimen in intact form and at two different decompression levels did not significantly differ (P > 0.05). However, under flexion motion, intervertebral displacement of the laminectomy specimens at decompression level L4-L5 was statistically greater than in intact or bilateral laminotomy specimens (P = 0.0000963 and P = 0.000418, respectively). No difference was found between intact and bilateral laminotomy groups. (P > 0.05).

Conclusion: We concluded that a lumbar spine with posterior complex integrity is less likely to develop segment instability than a lumbar spine with a destroyed anchoring point for supraspinous ligament.

Figure 1

Lateral View and posterior view of lumbar spine after (A) laminectomy and (B) bilateral laminotomy. In laminectomy, the lamina and spinous processes of lower L4 and upper L5 are removed by rongeur and Kerrison clamp. The ligamentum flavum and supraspinous ligament of L4–L5 are removed. In laminotomy, fenestration is made on both sides. The inferior margin of L4 lamina and superior margin of L5 lamina are removed by burr. The L4–L5 ligamentum flavum is removed.

Figure 2

Photograph of the lumbar spine (A) intact, and at two different levels of decompression following (B) bilateral laminotomy and (C) laminectomy.

Figure 3

Photograph of the (A) experimental setup for measuring intervertebral displacement and (B) flexion motion of intact lumbar spine. By using a specially designed fixture, an 8,400 N-mm constant moment generated through the axial movement of the MTS actuator was applied to the spine specimen to achieve flexion and extension motions. Intervertebral displacement at L4–L5 adjacent to the fusion level was recorded continuously using an MTS extensometer.

Figure 4

A diagram of a typical intervertebral displacement versus applied moment on the decompressive segment under flexion motion. The curve pattern demonstrates a significant decrease in intervertebral displacement of the decompressive segment as flexion moment increases in the early period. However, the rate (slope) gradually decreased as flexion moment increased.

Figure 5

Intervertebral displacement of L3–L4 segment under flexion and extension motions (8400 N-mm). Intervertebral displacement between three different decompressive procedures under extension motion did not significantly differ (P > 0.05). However, under flexion motion, intervertebral displacement in the laminectomy group was statistically higher than in the intact or bilateral laminotomy groups (P < 0.05).