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Heterotopic Ossification in Total Cervical Artificial Disc Replacement

Mehren, Christoph MD*; Suchomel, Petr MD, PhD; Grochulla, Frank MD*; Barsa, Pavel MD; Sourkova, Petra MD; Hradil, Jan MD; Korge, Andreas MD*; Mayer, H Michael MD, PhD*

doi: 10.1097/01.brs.0000245852.70594.d5
Cervical Spine

Study Design. Prospective clinical study enrolled in 2 centers (Munich and Liberec) as part of a prospective European multicenter study with ProDisc C (Synthes Inc., Paoli, PA).

Objectives. The first goal of the study was to evaluate the rate of heterotopic ossifications identified with plain radiograph following total cervical disc replacement (TCDR). The second goal was to show whether segmental motion can be preserved, and whether TCDR can provide improvement of the patient’s ability to perform activities of daily living as well as a decrease of pain.

Summary of Background Data. Only a few reports about the radiologic outcome after TCDR are published so far. Heterotopic ossification is a well-known phenomenon after total hip arthroplasty. The rate of heterotopic ossification following TCDR is unclear.

Methods. The radiographs of 54 patients (in total, 77 implanted prostheses) were analyzed 1 year after TCDR with a ProDisc C prosthesis. We classified the heterotopic ossification in 5 grades according to a recently published classification system for lumbar total disc replacement. For clinical parameters, the visual analog scale and the Neck Disability Index were evaluated preoperatively and 1 year postoperatively. The Student t test and Wilcoxon test were used for statistical analysis.

Results. In 26 treated segments (33.8%), no heterotopic ossification was detectable. Grade 1 ossifications were present in 6 levels (7.8%). A total of 30 segments (39.0%) showed grade 2 ossifications. Heterotopic ossifications that led to restrictions of the range of motion were present in 8 cases (10.4%). One year postoperatively, 7 cases (9.1%) had a spontaneous fusion of the treated segment. The clinical parameters improved significantly and were similar to previous reports about TCDR.

Conclusions. Only 33.8% of the patients did not show any signs of heterotopic ossification, and the rate of spontaneous fusion after TCDR 1 year after surgery was unexpectedly high. There were 49.4% of the patients with grade 2-3 ossification, which lets us suspect an even higher rate of spontaneous fusion after long-term follow-ups. Motion preservation after TCDR is only guaranteed if spontaneous fusion can be prevented. Thus, mobility of the implanted segments needs to be further studied.

The radiographs of 54 patients treated with the ProDisc C cervical artificial disc (Synthes Inc., Paoli, PA) implanted in 77 segments were examined. In the 1-year follow-up, we observed 7 spontaneous fusions and another 8 high-grade heterotopic ossifications. The fusion rate of 9.1% as well as an overall of 66.2% heterotopic ossification 1 year after surgery was higher than expected.

From the *Spine Center Munich, Orthozentrum, Munich, Germany; and †Department of Neurosurgery, Neurocenter, Regional Hospital, Liberec, Czech Republic.

Acknowledgment date: November 22, 2005. First revision date: February 3, 2006. Acceptance date: February 8, 2006.

The device(s)/drug(s) that is/are the subject of this manuscript is/are not FDA-approved for this indication and is/are not commercially available in the United States.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Christoph Mehren, MD, Orthozentrum München-Orthopädische Klinik, Harlachinger Str. 51, 81547 München, Germany; E-mail:

© 2006 Lippincott Williams & Wilkins, Inc.