Spinal Instrumentation after Complete Resection of the Last Lumbar Vertebra: An In Vitro Biomechanical Study after L5 Spondylectomy

Study Design. Human cadaveric ilio-lumbosacral spines were tested in an in vitro biomechanical flexibility experiment to investigate the biomechanical stability provided by four different types of spinal reconstruction techniques after spondylectomy of the L5 vertebral body. Objective. To compare the biomechanical stability provided by four reconstruction methods after L5 spondylectomy. Summary of Background Data. Clinical studies have shown that total spondylectomy of the L5 vertebral body presents a challenging scenario for spinal reconstruction. Biomechanical studies on spinal reconstruction after total spondylectomy have been performed at the thoracolumbar junction. However, there have been no biomechanical studies after L5 spondylectomy. Methods. Seven cadaveric lumbosacral spines (L2-S1) with intact ilium were used. After intact testing, spondylectomy of the L5 vertebra was performed and the spine was reconstructed using an expandable cage for anterior column support. Supplementary fixation was performed as a sequential order of: (1) bilateral pedicle screws at L4-S1 (SP), (2) anterior plate and bilateral pedicle screws at L4-S1 (ASP), (3) bilateral pedicle screws at L3-S1 and iliac screws (MP), and (4) anterior plate at L4-S1, bilateral pedicle screws at L3-S1 and iliac screws (AMP). Range of motion (ROM) for each construct was obtained by applying pure moments in flexion, extension, lateral bending, and axial rotation. Results. In flexion, extension and lateral bending all the instrumented constructs significantly decreased (P < 0.05) the range of motion (ROM) compared to intact. In axial rotation, only the circumferential support constructs (ASP, AMP) provided significantly decreased (P < 0.05) ROM, whereas posterior instrumentations alone (SP, MP) were comparable to intact spines. Conclusion. After L5 spondylectomy, the L4-S1 cage with posterior short segment instrumentation provides stability in lateral bending that is not further increased by adding L3 pedicle-iliac screws and L4-S1 anterior plate. However, an anterior L4-S1 plate provides additional stability in flexion, extension, and axial rotation.