Kinematic efficacy of supplemental anterior lumbar interbody fusion at lumbosacral levels in thoracolumbosacral deformity correction with and without pedicle subtraction osteotomy at L3: an in vitro cadaveric study.

PURPOSE: Pedicle subtraction osteotomy (PSO) is performed to treat rigid, sagittal spinal deformities, but high rates of implant failure are reported. Anterior lumbar interbody fusion has been proposed to reduce this risk, but biomechanical investigation is lacking. The goal of this study was to quantify the (1) destabilizing effects of a lumbar osteotomy and (2) contribution of anterior lumbar interbody fusion (ALIF) at the lumbosacral junction as recommended in literature.

METHODS: Fourteen fresh human thoracolumbosacral spines (T12-S1) were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). Bilateral pedicle screws/rods (BPS) were inserted at T12-S1, cross connectors (CC) at T12-L1 and L5-S1, and anterior interbody spacers (S) at L4-5 and L5-S1. In one group, PSO was performed in seven specimens at L3. All specimens were sequentially tested in (1) Intact; (2) BPS; (3) BPS + CC; (4) BPS + S; and (5) BPS + S + CC; a second group of seven spines were tested in the same sequence without PSO. Mixed-model ANOVA with repeated measures was performed (p ≤ 0.05).

RESULTS: At the osteotomy site (L2-L4), in FE, BPS, BPS + CC, BPS + S, BPS + CC + S reduced motion to 11.2, 12.9, 10.9, and 11.4%, respectively, with significance only found in BPS and BPS + S construction (p ≤ 0.05). All constructs significantly reduced motion across L2-L4 in the absence of PSO, across all loading modes (p ≤ 0.05). PSO significantly destabilized L2-L4 axial rotational stability, regardless of operative construction (p ≤ 0.05). Across L4-S1 and L2-S1, all instrumented constructs significantly reduced motion, in both PSO- and non-PSO groups, during all loading modes (p ≤ 0.05).

CONCLUSIONS: These findings suggest anterior interbody fusion minimally immobilizes motion segments, and interbody devices may primarily act to maintain disc height. Additionally, lumbar osteotomy destabilizes axial rotational stability at the osteotomy site, potentially further increasing mechanical demand on posterior instrumentation. Clinical studies are needed to assess the impact of this treatment strategy.