Effect of Prosthesis Width and Depth on Heterotopic Ossification After Cervical Disc Arthroplasty

Study Design. Retrospective analysis. Objective. To investigate the effect of width and depth of the inserted cervical disc prosthesis on heterotopic ossification (HO) after cervical disc arthroplasty, and to explore the relationship between clinical outcome and HO. Summary of Background Data. The mechanism of HO formation still remains unknown. Footprint mismatch of cervical disc prosthesis was common in cervical arthroplasty. Compared with endplate, some inserted prostheses were smaller in width and length. Methods. Retrospectively analyze the patients who underwent cervical disc arthroplasty with Prestige-LP Disc in our institute. Patients were divided into HO group or non-HO group according to the McAfee classification. The ratios of the width (Rw) and depth (Rd) of prosthesis to endplate were calculated. Radiographic and clinical assessments included: C2-7 angle, segmental angle, range of motion (ROM) of the index level, visual analogue scale, neck disability index, and Japanese orthopaedic association scores. Results. The mean follow-up time was 47.7 months. At the last follow-up, the overall incidence of HO was 34.3% (35/102). There were 35 patients in the HO-group, and 67 patients in the non-HO group. The overall Rw and Rd were 0.887 = 0.057 and 0.927 = 0.048, respectively. Both the Rw and Rd of HO-group were smaller than those of non-HO group (0.869 vs. 0.897, P 1/4 0.033; 0.888 vs. 0.948, P< 0.001). There were no significant differences in visual analogue scale, neck disability index, or Japanese orthopaedic association scores, C2-7 angle, or segmental angle between the two groups. But the HO group had less ROM of the index level than the non-HO group (5.38 vs. 9.08). Conclusion. Some of prosthesis had insufficient coverage to the endplate in width and depth. Insufficient coverage of endplate in width and depth may induce the formation of HO. HO could reduce the ROM of the index level, but did not influence the clinical outcome.