Cervical Total Disc Replacement and Heterotopic Ossification: A Review of Literature Outcomes and Biomechanics

Abstract

Anterior cervical discectomy and fusion (ACDF) immobilizes surgical segments and can lead to the development of adjacent segment degeneration and adjacent segment disease. Thus, cervical total disc replacement (CTDR) has been developed with the aim to preserve the biomechanics of spine. However, heterotopic ossification (HO), a complication following CTDR, can reduce the segmental range of motion (ROM) and defects the motion-preservation benefit of CTDR. The pathological process of HO in CTDR remains unknown. HO has been suggested to be a self-defense mechanism in response to the non-physiological biomechanics of the cervical spine following CTDR. The current literature review is concerned with the association between the biomechanical factors and HO formation and the clinical significance of HO in CTDR. Endplate coverage, disc height, segmental angle, and center of rotation may be associated with the development of HO. The longer the follow-up, the higher the rate of ROM-limiting HO. Regardless of the loss of motion-preservation benefit of CTDR in patients with HO, CTDR confers patients with a motion-preservation period before the development of ROM-limiting HO. This may delay the development of adjacent segment degeneration compared with ACDF. Future clinical studies should explore the association between HO and changes in biomechanical factors of the cervical spine.

Cervical Total Disk Replacement

“…Motion-limiting HO is undesirable and negates the purpose of motion-preserving TDR. It has been reported that implanting TDRs of greater heights has been associated with developing HO 10–12. This may be related to the biomechanical studies finding that implanting a TDR that is greater that natural height reduces ROM of the operated segment 17,18.…”

“…It has been reported that implanting TDRs of greater heights has been associated with developing HO. [10][11][12] This may be related to the biomechanical studies finding that implanting a TDR that is greater that natural height reduces ROM of the operated segment. 17,18 The reduced motion may allow greater one growth around the prosthesis.…”

“…These studies found that increased implant height was associated with decreased range of motion (ROM), [4][5][6][7] reduced facet overlap, possibly altering the loading of the adjacent facet joints which may impact the motion of the index level as well as loading of the adjacent segments, 4,5,8,9 and also related to the development of heterotopic ossification (HO). [10][11][12] With respect to implant height, one study found that in 36% of a study population, the height of the cervical disk space was less than the minimal height of available TDRs, which is generally 5 mm. 13 The purposes of the current study were to: (1) measure the heights of the disk spaces adjacent to the treated level (providing insight to normal disk height);…”

“…Several biomechanical studies involving cervical TDR have investigated the potential impact of prosthesis height, particularly with respect to implant sizes larger than the natural height. These studies found that increased implant height was associated with decreased range of motion (ROM),4–7 reduced facet overlap, possibly altering the loading of the adjacent facet joints which may impact the motion of the index level as well as loading of the adjacent segments,4,5,8,9 and also related to the development of heterotopic ossification (HO) 10–12…”

Risk Factors for High-Grade Heterotopic Ossification After Total Disc Replacement: A Single-Center Experience of 394 Cases

“…Other studies have suggested that the development of HO is a self-defense mechanism in response to the nonphysiological biomechanics of the cervical spine. 9,19 The exact mechanisms for the formation and development of HO following TDR remain unclear and needs further exploration. Zhou et al 15 reported in a 5-year follow-up study on 51 patients who underwent Bryan TDR and suggested that the so-called HO reflects progressive bone formation in individuals already predisposed to forming bone.…”