#272 Heterotopic Ossification Following Cervical Artificial Disc Replacement May Promote Adjacent Segment Degeneration: A Minimum 5-year Follow-up Result

General Session: Cervical Motion Preservation

Presented by: Z. Feifei


Z. Feifei (1)
S. Yu (1)

(1) Peking University Third Hospital, Beijing, China


Background: The primary principle of cervical non-fusion technology is preserving segmental motion so as to decrease the degeneration of the adjacent level. Therefore, the post-operative heterotopic ossification (HO) or even the spontaneous fusion is definitely in contradiction with the conception of the technology. The aim of this study is to identify whether the occurrence of HO after cervical artificial disc replacement could induce adjacent segment degeneration (ASD) with a minimum 5-year follow-up period.

Method:A total of 39 patients with 47 segments (1-level 32 cases, 2-level 6 cases, 3-level 1 case) underwent Bryan cervical disc (Medtronic Sofamor Danek Inc, Memphis, TN) replacement from December, 2003 to September, 2007 were reviewed retrospectively. All cases were followed up for more than 5 years (range, 57-88 months; average, 63months). The occurrence of HO was investigated with the McAfee classification on cervical lateral X-Ray. We also evaluated degenerative appearance of both upper and lower segments on X-ray (included the presence of any of the following parameters: A, New anterior or enlarging osteophyte formation; B, Narrowing of disc spaceā‰„ 10%; C, Calcification of anterior longitudinal ligament) and MRI (degeneration deteriorating one more grade according to Miyazaki classification; the invasion ratio of disc protrusion to the spinal canal) through pre-operation to the final follow-up. These radiological parameters of ASDs were analyzed the correlation with the occurrence of HO.

Result: In 47 treated segments, a total of 17 HOs were detectable. The occurrence rate of HO was 36.2% and the classification of HO by McAfee criteria distributed as follows: Grade I 3 cases; Grade II 3 cases; Grade III 5 cases; Grade IV, which means loss of motion, 6 cases. 15 in 74 adjacent segments (20.3%) of 39 patients (4 segments were blocked by the patients' shoulder) developed ASDs by X-ray's criteria, and there was no statistical difference between HOs and non-HOs. In all the 39 patients, there were 34 patients had MRI follow-up data. 10 segments in 68 adjacent segments (14.7%) were assessed degeneration deteriorating one grade according to Miyazaki classification. The difference between HOs (53.8%) and non-HOs (14.3%) was statistical significant (p=0.02). The invasion ratio of disc protrusion was almost similar between pre-operation and final follow-up about 5 years after the surgery both for the upper and lower adjacent segments, and there was no statistical difference between HOs and non-HOs.

Conclusion: The incidence of HO after cervical arthroplasty was relatively high during a long term follow-up. HO may be one of the negative factor which promote ASD which displayed as disc signal deteriorating in MRI.