Clinical results and development of heterotopic ossification in total cervical disc replacement during a 4-year follow-up

Abstract

Cervical total disc replacement (CTDR) aims to decrease the incidence of adjacent segment disease through motion preservation in the operated disc space. Ongoing data collection and increasing number of studies describing heterotopic ossification (HO) resulting in decreased mobility of implants, forced us to carefully evaluate our long-term clinical and morphological results of patients with CTDR. We present the first 54 consecutive patients treated with 65 ProdiscC prostheses during a 12-month period (2/2004-3/2005). All patients signed an informed consent and were included in prospective long-term study approved by hospital ethical committee. The 1- and 2-year follow-up analysis were available for all patients included and 4-year results for 50 patients (60 implants). Clinical (neck disability index-NDI, visual analog scale-VAS) and radiological follow-up was conducted at 1-, 2- and 4-years after the procedure. The Mehren/Suchomel modification of McAfee scale was used to classify the appearance of HO. Mean preoperative NDI was 34.5%, VAS for neck pain intensity 4.6 and VAS for arm pain intensity 5.0. At 1-, 2- and 4-year follow-up, the mean NDI was 30.7, 27.2, and 30.4, mean VAS for neck pain intensity 2.5, 2.1 and 2.9 and mean VAS for arm pain intensity pain 2.2, 1.9 and 2.3, respectively. Significant HO (grade III) was present in 45% of implants and segmental ankylosis (grade IV) in another 18% 4 years after intervention. This finding had no clinical consequences and 92% of patients would undergo the same surgery again. Our clinical results (NDI, VAS) are comparable with fusion techniques. Although, advanced non-fusion technology is used, a significant frequency of HO formation and spontaneous fusion in cervical disc replacement surgery must be anticipated during long-term follow-up.

Fig. 1

HO grade 0: No signs of heterotopic ossification and full range of motion as seen on flexion (a), neutral (b) and extension (c) lateral cervical spine films at 4-year follow-up

Fig. 2

HO grade I: No signs of HO postoperatively (a) and a clear sign of heterotopic ossification grade I (b) on lateral cervical spine films at 4-year follow-up

Fig. 3

HO grade II: Clear signs of HO with no significant reduction in motion of the implant on flexion (a), neutral (b) and extension (c). Lateral cervical spine films, 4-year follow-up

Fig. 4

HO grade III: No signs of HO with satisfactory range of motion on postoperative lateral flexion (a) and extension (b) cervical spine films. The same patient on 4-year follow-up with significant heterotopic ossification limiting range of motion on flexion (c) and extension (d)

Fig. 5

HO grade IV: Fusion without any motion of treated segment(s) as seen on lateral cervical spine films of single-level (a), double-level (b), and triple-level (c) implantations

Fig. 6

Neck Disability Index (NDI) scores during investigated time period. Vertical bars denote 0.95 confidence intervals for means. Significant effect of operation in improvement of results was revealed using ANOVA. Post hoc analyses revealed significant difference from preoperative value at 3 months, 6 months and 2 years follow-up controls. *Significant difference from preoperative value

Fig. 7

VAS score for neck pain intensity during investigated time period. Vertical bars denote 0.95 confidence intervals for means. Significant effect of operation in improvement of results was revealed using ANOVA. Post hoc analyses revealed significant difference from preoperative value at all follow-up controls. *Significant difference from preoperative value

Fig. 8

VAS score for arm pain intensity during investigated time period. Vertical bars denote 0.95 confidence intervals for means. Significant effect of operation in improvement of results was revealed using ANOVA. Post hoc analyses revealed significant difference from preoperative value at all follow-up controls. *Significant difference from preoperative value