Anterior Bone Loss after Cervical Bryan Disc Arthroplasty: Insight into the Biomechanics following Total Disc Replacement.

ABSTRACT Background Context Cervical disc arthroplasty (CDA) is an innovative procedure launched in the early 2000s. Compared to anterior cervical discectomy and fusion, many studies show that CDA offers equivalent clinical outcomes while reducing secondary procedures and total cost. Purpose We sought to determine the incidence of anterior bone loss after CDA and the related biomechanical effects. Study Design/ Setting Retrospective chart review Patient Sample Patients who underwent CDA with one level Bryan Disc (Medtronic Sofamor Danek, Memphis, TN) at one institution. Outcome Measures Radiological measurements, including the extent of anterior bone loss, global alignment angle, shell angle, lordotic angle, mean degree of angle of the endplate with the horizontal line, global range of motion (ROM) and ROM of the index level were recorded. The grading of anterior bone loss of the index level was defined as: Grade 0, no remodeling; Grade 1, spur disappearance or mild change in body contour; Grade 2, obvious bone regression with Bryan Disc exposure. Methods Anatomical measures and ROM were compared by grade of bone loss. Results Of the 121 patients included in the study, anterior bone loss was found in 53 (43.8%) on the upper adjacent level and 54 (44.6%) on the lower adjacent level. Twenty-nine patients (23.9%) had anterior bone loss in both levels. The majority of cases had Grade 1 anterior bone loss. Grade 2 bone loss was noted in the upper adjacent vertebra in only 5 patients and in 4 patients in the lower adjacent vertebra. Age, sex, operative level and hybrid surgery had no effect on anterior bone loss. Most radiological assessments, including global alignment angle, lordotic angle, mean degree of angle of the endplate with the horizontal line, global ROM and ROM of the index level, showed no correlation to anterior bone loss. Shell angle was found to be different in groups with or without remodeling in the upper adjacent level: 5.0 degrees in the Grade 0 group and 7.0 degrees in the Grade 1-2 group, p Conclusions Many more patients than predicted had anterior bone loss. Increasing the shell angle of the artificial disc may increase the incidence of anterior bone loss after CDA. Further study of the biomechanics following CDA should help clarify the mechanisms at work.