A biomechanical evaluation of a spacer with integrated plate for treating adjacent-level disease in the subaxial cervical spine

Abstract

Adjacent level degeneration (ALD) has been reported as one of the long-term consequences of anterior discectomy and fusion despite its clinical success in treating cervical pathologies. Traditionally, ALD is treated by replacing the previously implanted plate with a longer plate, which can lead to postoperative complications. The biomechanics of SIP in the adjacent level has not been investigated. To evaluate the multidirectional stability of a spacer with integrated plate (SIP) in comparison to a traditional spacer and plate (TSP). To evaluate the biomechanical stability of a spacer with integrated plate adjacent to a traditional spacer and plate construct in a human cervical cadaveric model. Eight fresh human cervical (C2-C7) cadaver spines were mounted on a six degree-of-freedom spine simulator. The sequence of test constructs was: 1) Intact; 2) TSP (C4-C6) with SIP (C3-C4); and 3) TSP (C3-C6). An unconstrained moment of ±1.5 Nm was used in flexion-extension, lateral bending, and axial rotation. Range of motion (ROM) was measured by a digital motion analysis system. Statistical analysis was performed using ANOVA repeated measures. All instrumented constructs significantly reduced ROM compared to the intact condition. No statistically significant difference was observed between the two-level TSP with an adjacent SIP construct and three-level TSP construct in all loading modes. The biomechanical study shows that adding a spacer with integrated plate adjacent to a two-level anterior plate demonstrates equivalent stability to a three-level anterior plate. The spacer with integrated plate, which preserves the originally plated fusion levels, may overcome the complications associated with the traditional technique of replacing the original plate with a longer plate. However, prospective clinical studies are required to address the clinical benefits and challenges, if any.