Bone-Preserving Decompression Procedures Have a Minor Effect on the Flexibility of the Lumbar Spine

OBJECTIVE: To mitigate the risk of iatrogenic instability, new posterior decompression techniques able to preserve musculoskeletal structures have been introduced but never extensively investigated from a biomechanical point of view. This study was aimed to investigate the impact on spinal flexibility caused by a unilateral laminotomy for bilateral decompression, in comparison to the intact condition and a laminectomy with preservation of a bony bridge at the vertebral arch. Secondary aims were to investigate the biomechanical effects of two-level decompression and the quantification of the restoration of stability after posterior fixation. METHODS: A universal spine tester was used to measure the flexibility of six L2–L5 human spine specimens in intact conditions and after decompression and fixation surgeries. An incremental damage protocol was applied : 1) unilateral laminotomy for bilateral decompression at L3–L4; 2) on three specimens, the unilateral laminotomy was extended to L4–L5; 3) laminectomy with preservation of a bony bridge at the vertebral arch (at L3–L4 in the first three specimens and at L4–L5 in the rest); and 4) pedicle screw fixation at the involved levels. RESULTS: Unilateral laminotomy for bilateral decompression had a minor influence on the lumbar flexibility. In flexion-extension, the median range of motion increased by 8%. The bone-preserving laminectomy did not cause major changes in spinal flexibility. Two-level decompression approximately induced a twofold destabilization compared to the single-level treatment, with greater effect on the lower level. Posterior fixation reduced the flexibility to values lower than in the intact conditions in all cases. CONCLUSION: In vitro testing of human lumbar specimens revealed that unilateral laminotomy for bilateral decompression and bone-preserving laminectomy induced a minor destabilization at the operated level. In absence of other pathological factors (e.g., clinical instability, spondylolisthesis), both techniques appear to be safe from a biomechanical point of view.