ANTERIOR LONGITUDINAL LIGAMENT RECONSTRUCTION RESTORES BIOMECHANICAL STABILITY AFTER SURGICAL ANTERIOR APPROACH TO THE CERVICAL SPINE

Various degenerative pathologies of the cervical spine are routinely treated by an anterior surgical approach. However, adjacent segment degeneration or instability are common long-term complications that might arise from altered biomechanics after anterior longitudinal ligament (ALL) resection during the anterior approach. Therefore, the concept for this study utilizes the orthopedic principles of ligament reinforcement for joint stabilization, providing targeted anterior stabilization of the spine by ALL reconstruction, yet without rigidly immobilizing the segment. The aim of the study was to investigate the impact of ALL resection and whether ALL reconstruction provides equal biomechanical stability and range of motion compared to the intact state of the cervical spine. 10 spinal segments of 4 cadaveric human cervical spines (C2/3: 2, C3/4: 2, C4/5: 2, C5/6: 2, C6/7: 2) were tested in a stepwise surgical resection and stabilization study. Cervical vertebral bodies were fixed for biomechanical testing with 3D-printed clamps. ALL reconstruction was achieved with a surgical tape and human gracilis tendon allograft which were fixed to the bone by a bone anchor in each vertebral body. Each specimen was tested load-controlled in the native anatomic state, after destabilization by resection of the ALL and after ALL reconstruction. Range of motion (ROM) was tested for flexion-extension (FE), lateral shear (LS), lateral bending (LB) and anteroposterior shear (AS) and axial rotation (AR). Compared to the intact ALL state (100%), median relative ROM in FE increased to 131% [122%–163%] p < 0.01 after resection and 103% [93%–115%] p > 0.05 after reconstruction. The same trend was seen for LS, LB, AS and AR with the smallest effect in resection for AR: 111% [108%–125%] p < 0.05 and in reconstruction for LS: 116% [103%–119%] p < 0.05. Median absolute ROM for FE increased from the intact to reconstructed to resected state (8.5° [6.2°–11.7°], 10.0° [5.7°–12.9°], 12.1° [8.3°–14.3°], respectively). The ALL plays an important role for maintaining stability of the cervical spine across all directions of motion, with its greatest impact in flexion-extension and the least in axial rotation. Reconstruction of the ALL restores ROM to near its intact state in almost all loading directions, potentially lowering the complication rate associated with ligament resection in an anterior approach.