Toward understanding how altered trunk-pelvis motions and loads during walking after lower limb loss influence lumbar spine mechanics: Insights from ex vivo testing

Altered trunk-pelvis motions and loads during activities of daily living are biomechanical risk factors for low back pain after lower limb loss. This investigation evaluated the relative contributions of trunk-pelvis motions and loads to spinal laxity using a servohydraulic materials testing system to emulate walking biomechanics. Twelve porcine lumbar spines (age: 12–18 months, mass: 45–68 kg) were exposed to 6 different experimental conditions which comprised of all combinations of trunk-pelvis motion/load conditions (motion, load, and motion + load) and two cohorts (limb loss and uninjured), to Neutral zone (NZ) widths, as a measure of passive spinal laxity, were computed after a 20- minute repetitive exposure to each profile. NZ width was 18 % larger in lateral bend among the limb loss vs. uninjured cohort (p = 0.043) during the motion + load condition NZ width was 23 % larger in the uninjured vs. limb loss cohort when comparing the load-only condition (p < 0.001). In lateral bend, NZ width after the motion + load condition was 31 % larger compared to the motion-only (p = 0.039) and 23 % larger compared to load-only condition in the limb loss cohort only. Overall, NZ widths were smaller in the limb loss vs. uninjured cohort in both flexion/extension (p = 0.006) and axial twist (p = 0.014).Relative increases in NZ width after exposure to emulated walking profiles, particularly in the frontal plane, directly demonstrate that even short walking bouts in the limb loss population may induce acute changes in passive spinal structures.