Resection or degeneration of uncovertebral joints altered the segmental kinematics and load-sharing pattern of subaxial cervical spine: A biomechanical investigation using a C2-T1 finite element model.

The uncovertebral joint (UJ) is an important load-bearing structure in the subaxial cervical spine (SCS) and the medial wall of the intervertebral foramen (IVF). To investigate the UJ׳s role in load distribution and transmission under physiological loading, we developed and validated a detailed finite element model (C2-T1). Based on the initial model, two additional models were modified to simulate surgical resection and degeneration of UJs, to evaluate their influence on SCS kinematics and load distribution. The three models were subjected to 2Nm pure moment (flexion, extension, lateral bending, and axial rotation). Foraminal narrowing and potential nerve compression were evaluated. In the initial model, contact forces provided by the UJ were apparent in lateral bending and axial rotation. In axial rotation, the UJs and contralateral facet joints participated in joint activity, implying a possible restraint/counterbalance mechanism of these two joints. Peak vertebral stress was observed in the pedicle of vertebrae and was higher in the uncovertebral region than in the facet region. Resection of uncinate processes led to an apparent range of motion increase in lateral bending and axial rotation, while sagittal kinematics is influenced slightly. The load on other structures was slightly increased, but in axial rotation, resection of UJs changed the load distribution pattern. Degeneration of UJs significantly increased SCS stiffness and shielded other load-bearing structures. Peak IVF narrowing, but no nerve compression, was observed in axial rotation of the resection model. Thus, resection did not induce apparent secondary foraminal stenosis when other structures were still functional.