In vitro radiographic characteristics and biomechanical properties of the canine lumbar vertebral motion unit after lateral corpectomy, mini-hemilaminectomy and hemilaminectomy.

Objective: The purpose of this study was to assess the effect of three surgical procedures (left lateral corpectomy [LC], LC plus mini-hemilaminectomy [LC-MH], and LC plus hemilaminectomy [LC-H]) on the biomechanics and intervertebral collapse of a lumbar vertebral motor unit (VMU).Methods: Six canine cadaveric first and second lumbar vertebrae (L1-L2) VMU were retrieved. Range-of-motion (ROM) was measured while a custom-built mechanical simulator applied 3 Nm torque in lateral bending, flexion and extension to the intact VMU and following the three surgical procedures (LC, LC-MH, LC-H) performed sequentially. Radiographs were taken with and without 3 kg axial compression at each step.Results: Left lateral corpectomy and LC-MH significantly increased the ROM in left lateral bending and total lateral bending. A LC-H significantly increased the ventral, left, right, total lateral, and total dorsoventral ROM. Significant intervertebral collapse was observed after LC-H with and without axial compression, and after LC and LC-MH, but only with axial compression.Clinical significance: A LC induces significantly increased ROM in lateral bending to the side of the surgery and in total lateral ROM. Extending the LC to a LC-MH does not change the spinal column stability compared to LC alone, while it provides better access to the spinal canal. The LC-H further destabilizes the VMU. The finding of intervertebral collapse following these surgical procedures confirms the importance of the intervertebral disc and articular facet in the maintenance of spatial integrity.