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

Abstract

BackgroundThe 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. MethodsTwenty-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. FindingsThe 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. InterpretationThe 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.