Heterotopic ossification in total cervical artificial disc replacement.
METHODS
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).


OBJECTIVE
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.


BACKGROUND
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.
Mehren
Christoph
C
Spine Center Munich, Orthozentrum, Munich, Germany. cmehren@schoen-kliniken.de
Suchomel
Petr
P
Grochulla
Frank
F
Barsa
Pavel
P
Sourkova
Petra
P
Hradil
Jan
J
Korge
Andreas
A
Mayer
H Michael
HM
D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D017586:Diskectomy; D004867:Equipment Design; D005500:Follow-Up Studies; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D008866:Microsurgery; D009038:Motion; D019547:Neck Pain / Q000517:prevention & control; D009999:Ossification, Heterotopic / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D010147:Pain Measurement; D011183:Postoperative Complications / Q000453:epidemiology* / Q000209:etiology; D011446:Prospective Studies; D019736:Prostheses and Implants; D011859:Radiography; D016059:Range of Motion, Articular; D020127:Recovery of Function; D012720:Severity of Illness Index