POROUS COATED MOTION CERVICAL DISK REPLACEMENT – A BIOMECHANICAL, HISTOMORPHOMETRIC AND BIOLOGIC WEAR ANALYSIS IN A CAPRINE MODEL.

Abstract

Introduction The current study was undertaken to investigate the biomechanical and biologic in-growth characteristics of the Porous Coated Motion™ cervical disc prosthesis following a six and twelve-month implant duration using an in-vivo caprine model.

Methods Twelve mature Nubian goats were divided into two groups based on post-operative survival periods of six (n=6) and twelve months (n=6). Using an anterior surgical approach, a complete diskectomy was performed at the C3-C4, followed by implantation of the Porous Coated Motion™ device. Functional outcomes of the disc prosthesis were based on computed tomography (CT), multi-directional flexibility testing, undecalcifed histology, histomorphometry and immunocytochemical analyses.

Results There was no evidence of prosthesis loosening, neurologic or vascular complications. CT scans demonstrated the ability to image and assess the cervical spinal canal for the presence of compressive pathology in the area of the CoCrMo prosthesis. Multi-directional flexibility testing indicated no differences in full range of intervertebral motion between the disc prosthesis and non-operative controls (n=7) under axial rotation or lateral bending conditions (p> 0.05). Flexion-extension produced significantly more motion for the intact spine compared to the cervical disc prosthesis (p< 0.05). Based on immunohistochemical and histologic analysis, there was no evidence of particulate debris, cytokines or cellular apoptosis within the local tissues overlying the operative site or systemic tissues. Moreover, review of the spinal cord at the operative levels indicated no evidence of cord lesions, inflammatory reaction, wear particles or significant pathologic changes in any treatment. Histomorphometric analysis at the metal-bone interface indicated the mean trabecular ingrowth of 40.5±24.4% at six-months and 58.65% ± 28.04 at twelve months.

Discussion All twelve goats undergoing cervical disc replacement had no evidence of implant loosening or inflammatory reactions from particulate wear debris. Segmental intervertebral motion was preserved based on multi-directional flexibility testing. The TiCaP porous ingrowth surface provided some immediate advantages for endplate osseointegration as there was no evidence of implant subluxation, despite immediate post-operative unrestricted cervical activity. Following cervical disc replacement, histological osseointegration at the implant-bone interface is possible, while preserving segmental motion.