The correlation between patient selection and heterotopic ossification after cervical artificial disc replacement

Abstract

Objective To analysis the correlation between patient selection and heterotopic ossification (HO) after cervical artificial disc replacement. Methods Data of 48 patients with cervical spondylosis (34 cervical spondylotic myelopathy and 14 nerve-root type) who had undergone Bryan cervicadisc replacement from December 2003 to December 2008 were reviewed retrospectively, and all the patients had been followed up for more than 5 years. There were 21 males and 27 females with an average age of 42 years old (range, 20-53 years). There were 38 single level replacement (C3-4 3 cases, C4-5 5 cases, C5-6 28 cases, C6-7 2 cases), 9 double level replacement (C4-5, C5-6 4 cases; C5-6, C6-7 5 cases) and 1 three level replacement (C3-4, C4-5, C5-6) as a total of 59 surgical segments. The occurrence of HO was defined by McAfee classification on cervical lateral X-ray. Four factors were used in patient selection including gender, range of motion (ROM) of the target level, alignment of the functional spine unit (FSU) of the index level, and the disc height ratio between surgical level and the adjacent levels. The correlation between these four factors and HO was evaluated by logistic regression. The receiver operating characteristic (ROC) curve and area under the ROC curve were used to evaluate the significant result of logistic regression and the optimal diagnostic value. Results 48 patients were all followed up for an average period of 70.3 months (range, 60-120 months). The occurrence rate in this study was 33.9% (20/59 segments). Only one factor, the disc height ratio of the target level and its adjacent levels, presented statistical correlation with HO. ROC analysis showed that the area under the ROC curve of disc height ratio was 0.813 and the optimal diagnostic threshold was 0.9. Conclusion The disc height ratio of the target level and adjacent levels was the only patient selective factor correlated with the occurrence of HO. For those with disc height loss exceeding 10% comparing to adjacent levels, it is not indicated for cervical artificial disc replacement with Bryan prosthesis. Key words: Cervical vertebrae; Total disc replacement; Ossification, heterotopic