ProDisc-C: an in vivo kinematic study.

STUDY DESIGN

A prospective study of 22 patients with single-level cervical spondylosis.

OBJECTIVE

To quantify the changes in the biomechanics of the cervical spine after the insertion of a ProDisc-C (Synthes Spine, Paoli, PA) artificial disc.

SUMMARY OF BACKGROUND DATA

Cervical arthroplasty is designed to maintain cervical motion of the functional spinal unit (FSU) after cervical discectomy. The impact of the ProDisc-C on in vivo kinematics and sagittal alignment requires further assessment.

METHODS

Flexion/extension lateral radiographs of the cervical spine were prospectively collected and reviewed in 22 patients preoperatively and after the placement of ProDisc-C. Disc height (DH), FSU angle, range of motion (ROM), and center of rotation (COR) were calculated at each time point using validated, computer-assisted methods. Preoperative values were compared with the postoperative values using paired student t tests.

RESULTS

Mean follow-up time was 11.0 months (SD, 2.4 mo). At the surgical level, the ProDisc-C produced increased segmental ROM (P = 0.03), an anterior shift of 1.1 mm in COR X (P = 0.004), and increased DH both anteriorly (P < 0.0001) and posteriorly (P < 0.0001). At the inferior adjacent level, anterior DH decreased (P < 0.05) and posterior DH increased (P = 0.02) after surgery. The FSU angle at the surgical level increased (P < 0.0001), but the inferior adjacent-level FSU angle decreased (P = 0.002). No significant changes were observed at the superior adjacent level.

CONCLUSIONS

The ProDisc-C increased segmental ROM and shifted the COR anteriorly at the surgical level. DH increased at the surgical level. The surgical level became more lordotic, whereas the inferior adjacent level became more kyphotic after ProDisc-C implantation.