In vivo analysis of cervical kinematics after implantation of a minimally constrained cervical artificial disc replacement

Abstract

Introduction To better understand cervical kinematics following cervical disc replacement (CDR), the in vivo behavior of a minimally constrained CDR was assessed. Methods Radiographic analysis of 19 patients undergoing a 1-level CDR from C4-5 to C6-7 (DISCOVER, DepuySpine, USA) was performed. Neutral-lateral and flexionextension radiographs obtained at preop, postop and late follow-up were analyzed for segmental angle and global angle (GA C2-7). Flexion-extension range of motion was analyzed using validated quantitative motion analysis software (QMAÒ, Medical Metrics, USA). The FSU motion parameters measured at the index and adjacent levels were angular range of motion (ROM), translation and center of rotation (COR). Translation and COR were normalized to the AP dimension of the inferior endplate of the caudal vertebra. All motion parameters, including COR, were compared with normative reference data. Results The average patient age was 43.5 ± 7.3 years. The mean follow-up was 15.3 ± 7.2 months. C2-7 ROM was 35.9°± 15.7°at preop and 45.4°± 13.6°at follow-up (Dp\ .01). Based on the QMA at follow-up, angular ROM at the CDR level measured 9.8°± 5.9°and translation was 10.1 ± 7.8 %. Individuals with higher ROM at the CDR level had increased translation at that level (p \ .001, r = 0.97), increased translation and ROM at the supra-adjacent level (p \ .001, r = .8; p = .005, r = .6). There was a strong interrelation between angular ROM and translation at the supra-adjacent level (p \ .001, r = .9) and caudal-adjacent level (p\.001, r = .9). The location of the COR at the CDRand supra-adjacent levels was significantly different for the COR-X (p \ .001). Notably, the COR-Y at the CDR level was significantly correlated with the extent of CDR-level translation (p = .02, r = .6). Shell angle, which may be influenced by implant size and positioning had no impact on angular ROM but was correlated with COR-X (p = .05, r = -.6) and COR-Y (p = .04, r = -.5). Conclusion The COR is an important parameter for assessing the ability of non-constrained CDRs to replicate the normal kinematics of a FSU. CDR size and location, both of which can impact shell angle, may influence the amount of translation by affecting the location of the COR. Future research is needed to show how much translation is beneficial concerning clinical outcomes and facet loading.

Correlation between cervical lordosis and adjacent segment pathology after anterior cervical spinal surgery

“…patients had an HO grade greater than grade II and HO was a significant risk factor for RASP development. Recent in vivo analysis of cervical kinematics after minimally constrained CDA showed that maintaining physiological COR is difficult, whereas both angular and translation motion can be maintained or restored [28]. Theoretically, an ideal CDA surgical result simulates the intervertebral disk functions in term of ROM, COR, and shock absorption.…”

Heterotopic ossification and clinical outcome in nonconstrained cervical arthroplasty 2 years after surgery: the Norwegian Cervical Arthroplasty Trial (NORCAT)

“…However, an imprecise position of the implant may cause a negatively altered COR and perhaps influence HO formation. Assuming that replication of a physiologic COR is an important design feature of a cervical prosthesis, Koller et al found that ideal surgical preparation and ideal positioning of the implant are most important to preserve the segmental COR and balance [19].…”

“…Lateral motion is limited to 21°. The fixed inlay in combination with a ball-and-socket superior articulation with limited lateral motion has resulted in the device being described as minimally constrained [19].…”

Clinical Relevance of Cervical Kinematic Quality Parameters in Planar Movement

“…Although cervical arthroplasty has an advantage over ACDF in retaining cervical motion quality, the implant position and type of prosthesis in cervical arthroplasty impact cervical motion quality postoperatively. Different rotation centers in the prevalent artificial cervical discs produce different biomechanical performances.…”