Anterior Migration After Bryan Cervical Disc Arthroplasty: The Relationship Between Hyperlordosis and its Impact on Clinical Outcomes.

Abstract

Various modifications have been tested to prevent kyphosis after Bryan cervical disc arthroplasty (CDA). However, the migration of Bryan prostheses has not been systematically studied. This study investigated the cause of anterior migration (AM) and assessed the effect of AM on clinical and radiographic outcomes. We retrospectively reviewed 46 consecutive patients who underwent modified Bryan CDA between August 2006 and December 2010. We measured functional spinal unit, angle of operative disc space, range of motion, and sagittal alignment of cervical spine preoperatively, postoperatively, and at the final follow-up, and compared these values between the AM and non-AM groups. Clinical outcome was evaluated by scores for Japanese Orthopaedic Association, Neck Disability Index, and visual analog scale. AM occurred in 9/46 (19.6%) patients. Clinical outcomes in both groups were significantly improved compared with the preoperative scores (P < 0.05). However, the postoperative and final follow-up angle of operative disc space was more lordotic and the postoperative functional spinal unit significantly higher in patients in the AM group compared with the non-AM group (P < 0.05). At the final follow-up, patients with AM had significantly higher Neck Disability Index and neck visual analog scale scores (P < 0.05), partially restricted range of motion (4.9° vs. 7.4°; P < 0.05), and adjacent segment degeneration at 6 vertebral levels (46.2%). The intermediate clinical outcomes for patients treated with modified Bryan CDA were satisfactory; however, overcorrection of segmental lordosis may lead to AM of the prosthesis, which could restrict patient range of motion and cause postoperative neck pain.