Biomechanical Effects of A Unilateral Transforaminal Endoscopic Approach for Lumbar Decompression: A Cadaveric Study

Cadaveric biomechanics study.

This study characterizes biomechanical changes in spinal kinematics for varying degrees of unilateral resection of the superior articular process by way of a transforaminal endoscopic approach.

Transforaminal endoscopic approaches for decompression of the lumbar spine have emerged as a desirable alternative to posterior decompression because they are assumed to be less destabilizing, if at all, to the spine. However, while general clinical outcomes are well-supported, there is limited evidence explicitly quantifying the effect of a step-wise approach on postoperative segmental stability, and even fewer biomechanical studies.

Six lumbar cadaveric specimens were tested biomechanically for range of motion (ROM) in flexion/extension (FE), lateral bending (LB), and axial torsion (AT). Between flexibility tests, a measured section of the left superior articular process (SAP) of the inferior vertebrae was removed in four increments (passes). Collected outcome measures were ROM, neutral zone (NZ), and neutral zone stiffness (NZ stiffness) in both directions of loading.

Average ROM for intact specimens was 9.1°±1.0° in FE, 9.1°±1.4° in LB, and 3.0°±0.6° in AT. A one-way ANOVA revealed significance in ROM for LB, NZ in all three directions, and NZ stiffness at both loading modes in FE and LB. Post-hoc analysis showed that significant increases in LB ROM and significant decreases in stiffness occurred as early as the first pass. NZ in FE had significant increases at second and fourth passes.

Significant increases in ROM in LB and decreases in NZ stiffness in both LB and FE with even minimal resection of the superior articulating process suggest changes in spine kinematics. While the magnitude of changes may not be clinically meaningful in general, this cadaveric model represents a worst case for biomechanical changes.