Effect of mechanical loading on heterotopic ossification in cervical total disc replacement: a three-dimensional finite element analysis

The development of heterotopic ossification (HO) is considered one of the major complications following cervical total disc replacement (TDR). Even though previous studies have identified clinical and biomechanical conditions that may stimulate HO, the mechanism of HO formation has not been fully elucidated. The objective of this study is to investigate whether mechanical loading is a biomechanical condition that plays a substantial role to decide the HO formation. A finite element model of TDR on the C5-C6 was developed, and HO formation was predicted by simulating a bone adaptation process under various physiological mechanical loadings. The distributions of strain energy on vertebrae were assessed after HO formation. For the compressive force, most of the HO formation occurred on the vertebral endplates uncovered by the implant footplate which was similar to the Type 1 HO. For the anteriorly directed shear force, the HO was predominantly formed in the anterior parts of both the upper and lower vertebrae as the Type 2 HO. For both the flexion and extension moments, the HO shapes were similar to those for the shear force. The total strain energy was reduced after HO formation for all loading conditions. Two distinct types of HO were predicted based on mechanically induced bone adaptation processes, and our findings were consistent with those of previous clinical studies. HO formation might have a role in compensating for the non-uniform strain energy distribution which is one of the mechanical parameters related to the bone remodeling after cervical TDR.