Impact of lamina preservation height during posterior decompression on lumbar biomechanical stress distribution: a finite element study.

BACKGROUND

Posterior decompression techniques represent the cornerstone of surgical intervention for lumbar disc herniation (LDH), evolving from open procedures to minimally invasive approaches. While effective, these techniques invariably require some degree of lamina resection to access the pathological site, potentially compromising spinal stability. The biomechanical impact of the extent of laminar height preservation remains quantitatively undefined.

OBJECTIVE

This study employed three-dimensional finite element analysis (FEA) to quantitatively evaluate the influence of different lamina height preservation ratios during unilateral posterior decompression on the biomechanical stability of the L4/5 lumbar segment, aiming to provide a theoretical basis for optimizing surgical technique.

METHODS

A precise L1-L5 segment three-dimensional finite element model was constructed based on the CT data of a healthy adult male volunteer and validated. Left-sided Posterior decompression surgery was simulated at the L4/5 segment, creating four models: Group A (25% left lamina height preserved), Group B (50% preserved), Group C (75% preserved), and Group D (intact model, 100% preserved). All models simulated partial nucleus pulposus resection (≈ 20%) and posterior annulus fibrosus resection (≈ 3 × 5 mm). Loads simulating upright posture, flexion, extension, lateral bending, and axial rotation (350 N axial force + 10Nm torque) were applied. Peak stress and displacement changes in key structures (pedicles, inferior articular processes, nucleus pulposus and annulus fibrosus, L4 vertebral body) were calculated and compared.

RESULTS

Reduced lamina preservation ratios (especially ≤ 50%) led to a sharp increase in stress on the surgical side pedicle and articular processes (e.g., > 500% increase in articular process stress during extension), with stress concentrated on the pedicle's medial edge. Contralateral structures experienced significantly increased loads during lateral bending/rotation. Disc stress increased but relatively modestly (< 65%). The computational results from this single finite element model indicated that a 50% lamina preservation ratio may represent a potential critical threshold for significant biomechanical deterioration, beyond which the stress increase rate drastically decreased.

CONCLUSION

Preserving less than 50% of lamina height during posterior decompression severely compromises spinal stability. To minimize postoperative biomechanical risks based on this model, preserving at least 50% of the lamina height appears advisable. This study provides quantitative, biomechanically-grounded evidence that can serve as a reference for bone preservation in a wide spectrum of posterior spinal decompression procedures.