In vitro analysis of circumferential joint replacement, including bilateral facet joint replacement with lateral lumber disc prosthesis: a parametric investigation of disc sizing.

PURPOSE: Lateral lumbar disc prosthesis (LLDP) is an innovative device used to restore motion in select patients through a lateral retroperitoneal approach. No in vitro biomechanical studies have been published. Further, the potential for in toto circumferential joint restoration when use of this anterior disc is combined with facet replacement remains unqualified but signifies a potentially interesting clinical direction.

METHODS: Researchers conducted a biomechanical feasibility study of an LLDP designed to investigate parameters of disc sizing used with bilateral facet joint replacement in a cadaveric model. Tested constructs at L4-L5 included (1) intact, (2) LLDP, (3) LLDP + wide discectomy, (4) LLDP + bilateral facetectomy, and (5) LLDP + bilateral facet joint replacement (BFJR). Investigators tested instrumented constructs (2-5) with an LLDP at compact-fit and lax-fit heights and used raw data to perform statistical analysis by repeated measures analysis of variance (ANOVA), along with Student-Newman-Keuls post hoc analysis (p ≤ 0.05).

RESULTS: Increased height of the LLDP resulted in significantly less motion compared with intact. Widening the discectomy while using lax-fit sizing led to motion similar to intact in flexion-extension. As expected, motion was greater with lax-fit height than with compact-fit height in all loading modes and constructs, as is noted with a widened discectomy. The L4-L5 center of rotation was maintained regardless of placement of the LLDP.

CONCLUSIONS: After bilateral facetectomy, reconstruction of the three-joint complex achieved by combining the LLDP with BFJR may provide a viable alternative to current clinical treatment regimens.