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Implant Design and the Anchoring Mechanism influence the Incidence of Heterotopic Ossification in cervical Total Disc Replacement at 2-year follow-up.

STUDY DESIGN
Non-randomized prospective and single center clinical trial.


OBJECTIVE
The aim of this study was to determine whether the prosthesis design, and especially changes in the primary anchoring mechanism between the keel-based ProDisc C™ and the spike-based ProDisc Vivo™, affects the frequency of heterotopic ossification (HO) formation over time.


SUMMARY OF BACKGROUND DATA
The occurrence of motion-restricting HO and well as underlying risk factors has so far been a widely discussed, but not well understand phenomenon. The anchoring mechanism and the opening of the anterior cortex may be possible causes of this unwanted complication.


METHODS
40 consecutive patients treated with the ProDisc C and 42 consecutive patients treated with the ProDisc Vivo were compared with respect to radiological and clinical outcome, with 2 years of follow up. Clinical outcome scores included the Neck Disability Index (NDI), Visual Analogue Scale (VAS), arm and neck pain self-assessment questionnaires. Radiological outcomes included the segmental lordosis and range of motion (ROM) of the index-segment as well as the occurrence of HO.


RESULTS
The clinical outcome parameters improved in both groups significantly. (ProDisc C: VAS arm and neck pain from 6.3 and 6.2 preoperatively to 0.7 and 1.3; NDI from 23.0 to 3.7; ProDisc Vivo: VAS arm and neck pain from 6.3 and 4.9 to 1.4 and 1.6, NDI from 34.1 to 8.7; 2 year FU). The ProDisc Vivo cohort demonstrated a significantly lower incidence of HO compared to the ProDisc C group at 1 year FU (p=0.0005) and 2 years FU (p = 0.005). Specifically, high grade HO occurred in 9% vs 31%.


CONCLUSION
These findings demonstrate that prosthesis designs that allow primary anchoring without violation of the cortical surface help to reduce the incidence of severe ossification, possibly affecting the functionality and mobility of the artificial disc device over of time.


LEVEL OF EVIDENCE
3.