Bone loss of the superior adjacent vertebral body immediately posterior to the anterior flange of Bryan cervical disc.

Background: No previous reports have mentioned bone loss of the superior adjacent vertebra immediately posterior to the anterior flange of Bryan cervical disc (Medtronic Sofamor Danek, Memphis, TN, USA), which plays a central role to prevent posterior migration of the device. The purpose of this study is to describe a new potential complication, bone loss immediately posterior to the anterior total disc replacement (TDR) flange on the superior adjacent vertebra following the Bryan cervical TDR and to discuss the possible mechanism.
Methods: The authors retrospectively reviewed 37 patients undergoing cervical TDR with the Bryan cervical disc. The clinical and radiological outcome data were collected at 1, 3, 6, 12, 24, and 36 months postoperatively, and at last follow-up, which ranged from 42 to 113 moths (average, 60.1 months). Clinical evaluation included the visual analog scale and neck disability index, and the radiographic evaluation included measurements of the functional spinal unit range of motion on flexion and extension and identification of radiographic changes such as bone loss.
Results: The Bryan TDR showed good mid-term clinical and radiological outcomes. Interestingly, however, bone loss was noted immediately posterior to the TDR flange on superior adjacent vertebra in 3 total patients; at 3 months (n = 2) and 6 months (n = 1). Although the bone loss was increased up to 6 months, this did not progress and no degradation of clinical and radiological outcomes occurred at last follow-up.
Conclusions: Bone loss immediately posterior to the anterior TDR flange on the superior adjacent vertebra can occur in the early postoperative period due to possibly stress shielding effect. However, it did not result in clinical changes or increased rates of graft failure at last follow-up. A long-term follow-up study is mandatory to evaluate the long-term effects of the bone loss.