Biomechanical properties of posterior transpedicular–transdiscal oblique lumbar screw fixation with novel trapezoidal lateral interbody spacer: an in vitro human cadaveric model

Purpose To investigate biomechanical properties of posterior transpedicular–transdiscal (TPTD) oblique lumbar screw fixation whereby the screw traverses the inferior pedicle across the posterior disc space into the super-adjacent body and lateral trapezoidal interbody spacer. Methods Eight fresh–frozen osteoligamentous human cadaveric spines (L1–S1) were tested in flexion–extension (FE), lateral bending (LB), and axial rotation (AR), with pure bending moment set at 7.5 Nm. Surgical constructs included (1) intact spine; (2) bilateral pedicle screw (BPS) fixation at L3–L4; (3) TPTD screw fixation at L3–L4; (4) lateral L3–L4 discectomy; (5) TPTD screw fixation with lateral interbody spacer (TPTD+S); and (6) BPS fixation with lateral interbody spacer (BPS+S). Peak range of motion (ROM) at L3–L4 was normalized to intact for statistical analysis. Results In FE and LB, all posterior fixation with or without interbody spacers significantly reduced motion compared with intact and discectomy. BPS and BPS+S provided increased fixation in all planes of motion; significantly reducing FE and LB motion relative to TPTD ( p = 0.005, p = 0.002 and p = 0.020, p = 0.004, respectively). In AR, only BPS significantly reduced normalized ROM to intact ( p = 0.034); BPS+S provided greater fixation compared with TPTD+S ( p = 0.005). Conclusions Investigators found less stiffness with TPTD screw fixation than with BPS regardless of immediate stabilization with lateral discectomy and spacer. Clinical use should be decided by required biomechanical performance, difficulty of installation, and extent of paraspinal tissue disruption.