A long-term study of heterotopic ossification after consecutive double-segment Bryan artificial cervical disc replacement

English Keywords:Bryan artificial intervertebral disc  Cervical spondylosis  Heterotopic ossification  Long-term follow-up

English Abstract:

  【Abstract】 Objectives: To observe the long-term follow-up outcome of cases underwent continuous double-segment Bryan artificial disc replacement over 8 years. Methods: A total of 21 patients who underwent con?鄄tinuous double segment artificial cervical disc replacement in our hospital from Jan 2004 to Dec 2011 were enrolled. Among them, 4 cases presented radiculopathy, 15 cases myelopathy, and 2 cases mixed type. There were 14 cases of C4/5 and C5/6 disc replacement, 2 cases of C5/6 and C6/7 disc replacement, and 5 cases of C3/4 and C4/5 disc replacement. The mean follow-up time was 116.5±19.6 months. mJOA and VAS scores were recorded at pre-operation, 3 months after surgery and final follow-up. The patients′ segmental range of motion (ROM) was measured on the cervical dynamic X-ray film. The cervical lordosis was measured by lat?鄄eral cervical X-ray film at final follow-up. The ectopic ossification of the artificial disc was evaluated on the cervical lateral X-ray film using McAfee classification method. Results: The mJOA score of 21 patients was 14.0±2.0 points at preoperation, 15.2±1.8 at 3 months after surgery, and 16.8±1.2 at final follow-up. There were statistical differences between the postoperative scores andpreoperation score(P<0.05). The preoperative VAS score was 5.1±1.7 points, and the VAS score 3 months after surgery was 1.9±1.4, the VAS score at fi?鄄nal follow-up was 0.9±0.8. The differences between the postoperative scores and preoperation score were with statistical significance. The cervical curvature before surgery was 16.7°±6.6° on average. The average cervical lordosis was 15.7°±7.3° at final follow-up. There was no statistical difference between that of preoperation and final follow-up (P=0.25). At final follow-up, the upper segment ROM was 6.23°±10.13° and the lower segment ROM was 3.76°±4.81°, the difference was with statistical significance(P=0.025). 16 cases developed heterotopic ossification at final follow-up, with an incidence of 76.2%. According to McAfee classification, among the 42 segments of 21 patients, 5 segments were of level Ⅰ, 5 segments level Ⅱ, 14 segments level Ⅲ, and 7 seg?鄄ments level Ⅳ. The probability of HO with level Ⅲ and above was 50%. Furthermore, it was found that the occurrence rate of level Ⅲ and Ⅳ HO in the upper segment was 38.0%, and that in the lower segment was 61.9%. The incidence of HO in the posterior vertebral margin of the lower segment was 71.4%, and that in the upper segment was 42.9%. Conclusions: The present study revealed a high incidence of ectopic ossifica?鄄tion after continuous double-segment Bryan cercical disc replacement at the long-term follow-up, and the low?鄄er segment is more likely to have severe HO.