“Remarkable” rate of heterotopic ossification after 10 years in cervical disc replacement patients


Although cervical total disc replacement remains a safe and effective procedure with low rates of complication and high levels of patient satisfaction, in patients with adjacent segment degeneration, significant heterotopic ossification and resulting loss of prosthesis function was observed at 10 years’ follow-up. The 10-year data was presented at EUROSPINE 2015 (2–4 September, Copenhagen, Denmark).

Christoph Mehren, Schӧn Klinik München Harlaching, Munich, Germany, and colleagues were reporting data from their ongoing prospective, non-randomised, single-centre clinical and radiological trial examining the use of the ProDisc-C (DePuy Synthes) artificial cervical disc as an alternative to anterior cervical discectomy and fusion (ACDF).

In their investigation, 50 patients (mean age of 46 years) were implanted with a total of 70 prosthesis, with follow-up data collected at one, five and 10 years postoperatively. Three patients dropped out of the study and follow-up rate of the remaining 47 patients at 10 years was 80.8% (n=38).

Clinical outcome measures used were the Neck Disability Index (NDI) and Visual Analogue Scale (VAS) alongside clinical parameters including patient satisfaction rate, employment status, complication rate and reoperation rate. The researchers also used X-ray evaluation to measure the incidence of heterotopic ossification and adjacent segment degeneration.

Mehren reported that the cervical disc replacement procedure produced “excellent clinical outcomes”. Results revealed that VAS neck scores fell from 6.4 to 1.9 and VAS arm scores fell from 6.3 to 2.1 at 10-year follow-up, both of which were statistically significant.

NDI scores also saw a stable improvement, from 21/50 at baseline to 6/50 at latest follow-up. Patient satisfaction was impressive, with 78.9% of all patients “highly satisfied” with their treatment after 10 years (and the remaining 21.1% “satisfied”), with 92.1% reporting that they would make the decision to undergo the same surgery again. The majority (85.7%) of patients were able to return to work without any restrictions, and only one went on to apply for disability pension, although Mehren noted that this “was not just as a result of the cervical disc replacement, as there were several other reasons for this application”. Complication rates (excluding heterotopic ossification) were low (12%, n=6) and the device-related revision surgery rate was just 2.2%.

The incidence of adjacent segment degeneration was 32.3%, 70% of which was asymptomatic and none of which required further surgery. Of those patients who developed adjacent segment degeneration, 80% presented with high-grade heterotopic ossification at five years’ follow-up, with a “significant progression of ossification over time” and resulting reduced function of the prosthesis—a “remarkable” finding, said Mehren. The authors of the study proposed that the high rate of adjacent segment degeneration could be a direct result of the ossification and loss of function of the device.

The high rates of ossification prompted a discussion from the audience, with some delegates asking whether cervical disc replacement simply represented a more expensive version of fusion. Mehren disagreed with this suggestion, and said that “if function is improved for five years, then that patient—in what is a young patient population—gains five years of value and motion before the prosthesis fuses. With the right indications, they are still excellent patients for this treatment. Ossification is not immediate—it is an ongoing change.”