Biomechanical study of unilateral pedicle screw combined with contralateral translaminar facet screw in transforaminal lumbar interbody fusion

Abstract

Background: The biomechanical stability of unilateral pedicle screw (UPS) combined with contralateral translaminar facet screw (TLFS), especially long-term stability, still needs to be compared to traditional UPS or bilateral pedicle screws (BPSs) in details.

Methods: Twenty-four porcine spines (L2-L5) were tested for flexibility with pure moments of 5Nm under intact status and transforaminal lumbar interbody fusion status using UPS+TLFS, UPS or BPS at L3-L4. After short-term (3cycles) and long-term cyclic loading (18,000cycles), the range of motion was obtained and analyzed for single-level constructs in flexion/extension, lateral bending and axial rotation modes. In addition, the relative displacement of contralateral articular processes was recorded in a real time fashion.

Findings: The range of motion was significantly reduced in all instrumented constructs. In all movement directions, UPS+TLFS achieved similar range of motion to BPS after short and long-term loading, which were significantly lower than that in UPS. A significantly larger displacement of contralateral articular process was recorded in UPS than UPS+TLFS and BPS during extension/flexion, lateral bending and axial rotation, suggesting its compromised stability.

Interpretation: The hybrid construct of UPS+TLFS showed instant and long-term equivalent biomechanical ability to that of traditional BPS, making it an alternative option to BPS that could be less invasive while maintains a stable and effective instrumentation.

Keywords: Biomechanics; Facet screw; Pedicle screw; Transforaminal lumbar interbody fusion.