[Impact of heterotopic ossification after single-level cervical disc replacement on adjacent segment]

Objective: To investigate the impact of heterotopic ossification (HO) after cervical disc replacement (CDR) on clinical outcome and radiological outcome of adjacent segment. Methods: The data of patients underwent single-level Prestige-LP CDR between January 2008 and March 2014 in West China Hospital with a minimum 36 months of follow-up were retrospectively analyzed in this study. The incidence of HO, whether it affected clinical outcome, and its impact on adjacent segment intervertebral disc height (IDH), range of motion (ROM) and adjacent segment degeneration were observed. The data were compared with independent sample t test between the two groups. Results: Ninety-two patients were included in this study, including 48 males and 44 females, the mean age was (44±8) years, and the mean follow-up was (62±23) months. At the final follow-up, 34 patients developed HO after CDR, but the incidence of Grade 4 HO was 7.6%. In both of the HO and non-HO groups, clinical outcomes at the final follow-up were all significantly improved when compared to those before the operation. And there was no significant differences in any clinical indexes between the HO and non-HO groups. The adjacent segment IDH before operation and at the final follow-up in the HO group and non-HO group were similar(t=0.596, 0.825 and t=0.877, 0.644, all P>0.05). The preoperative adjacent segment ROM of HO group was similar with that in non-HO group(t=0.056, 0.709, both P>0.05), but the adjacent segment ROM in HO group was higher than that in the non-HO group at the final follow-up (upper adjacent segment: 10.0°±2.0° vs 9.0°±1.3°; lower adjacent segment: 10.2°±1.9° vs 8.8°±1.3°, t=2.824, 4.022, both P<0.05). The incidence of adjacent segment degeneration of HO group was higher than that of non-HO group at the final follow-up(41.2% vs 19.0%, χ(2)=5.343, P<0.05). Conclusions: HO is a common phenomenon in the long-term follow-up after the CDR operation with Prestige LP prosthesis, but HO does not affect the improvement of clinical outcome. HO after CDR might be one of important risk factors accelerating adjacent segment degeneration.