Effect of cervical spine motion on displacement of posterolateral annulus fibrosus in cervical spondylotic radiculopathy with contained posterolateral disc herniation: a three-dimensional finite element analysis

BACKGROUND: Previous studies on dynamic impingement of nerve root in cervical spondylotic radiculopathy (CSR) have focused on effect of cervical spine motion (CSM) on dimensional changes of intervertebral foramen. However, there are few studies to investigate effect of CSM on displacement of posterolateral intervertebral disc until now. The present study aimed to investigate effect of CSM on displacement of posterolateral annulus fibrosus (AF) in CSR with contained posterolateral disc herniation. METHODS: A C5–C6 CSR finite element model with unilateral contained posterolateral disc herniation was generated based on validated C5–C6 normal finite element model. Forward and backward displacement distributions of posterolateral AFs in CSR model and normal model were compared. Changes in forward and backward displacement magnitudes of posterolateral AFs of the herniated side and the healthy side in CSR model, with respect to those of the ipsilateral posterolateral AFs in normal model, were compared. The comparisons were performed under flexion, extension, lateral bendings and axial rotations. RESULTS: There was no difference in deformation trend of posterolateral AF between CSR model and normal model. Bilateral posterolateral AFs mainly moved forward during flexion and backward during extension. Left posterolateral AF mainly moved backward and right posterolateral AF forward during left lateral bending and left axial rotation. Left posterolateral AF mainly moved forward and right posterolateral AF backward during right lateral bending and right axial rotation. However, with respect to forward and backward displacement magnitudes of the ipsilateral posterolateral AFs in normal model, those of the herniated side increased relatively significantly compared with those of the healthy side in CSR model. CONCLUSIONS: Flexion, lateral bending to the healthy side and axial rotation to the healthy side make posterolateral AF of the herniated side mainly move forward, whereas extension, lateral bending to the herniated side and axial rotation to the herniated side make it mainly move backward. These data may help select CSM or positions to diagnose and treat CSR with contained posterolateral disc herniation. Increase in deformation amplitude of posterolateral AF of the herniated side may also be the reason for dynamic impingement of nerve root in CSR with contained posterolateral disc herniation.