Prediction of heterotopic ossification on the cervical spine with offset of the artificial disc – A finite element study

Heterotopic ossification (HO) is a significant complication of cervical total disc replacement (TDR), often leading to fusion and negating the intended benefits of motion preservation. Although clinical factors associated with HO formation are known, the exact biomechanical mechanism remains unclear. This study aims to predict HO formation after Mobi-C disc replacement at the C5-C6 level using a validated finite element model (FEM) of the cervical spine (C2-T1) under physiological loading. The results revealed that the Mobi-C disc increased the range of motion (ROM) at the implanted level by 52 % under flexion and extension, while adjacent levels exhibited a 2–5 % reduction. Following HO formation, ROM at the implanted level decreased by 67–76 % in flexion and extension, respectively, while adjacent levels showed a moderate increase of 5–8 %. Additionally, intradiscal pressure at the adjacent levels increased by up to 60 % in extension, mimicking fusion-like behavior. HO volume was 678 mm³ for the ideal implant position, to 760 mm³ (+12 %) for a 0.5 mm offset and 800 mm³ (+17 %) for a 1 mm offset. This study highlights the importance of Mobi-C placement to minimize HO formation, preserve motion, and mitigate complications, providing insights for clinical practice.