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

Background: 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.

Objective: To evaluate the multidirectional stability of a spacer with integrated plate (SIP) in comparison to a traditional spacer and plate (TSP).

Methods: 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. Methods: 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.

Results: 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.

Conclusions: 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.