Determination of torque-limits for human and cat lumbar spine specimens during displacement-controlled physiological motions

Abstract

Background context Quadruped animal models have been validated and used as biomechanical models for the lumbar spine. The biomechanics of the cat lumbar spine has not been well characterized, even though it is a common model used in neuromechanical studies. Purpose Compare the physiological ranges of motion and determine torque-limits for cat and human lumbar spine specimens during physiological motions. Study design/setting Biomechanics study. Patient sample Cat and human lumbar spine specimens. Outcome measures Intervertebral angle (IVA), joint moment, yield point, torque-limit, and correlation coefficients. Methods Cat (L2–sacrum) and human (T12–sacrum) lumbar spine specimens were mechanically tested to failure during displacement-controlled extension (E), lateral bending (LB), and axial rotation (AR). Single trials consisted of 10 cycles (10 mm/s or 5°/s) to a target displacement where the magnitude of the target displacement was increased for subsequent trials until failure occurred. Whole-lumbar stiffness, torque at yield point, and joint stiffness were determined. Scaling relationships were established using equations analogous to those that describe the load response of elliptically shaped beams. Results IVA magnitudes for cat and human lumbar spines were similar during physiological motions. Human whole-lumbar and joint stiffness magnitudes were significantly greater than those for cat spine specimens (p<.05). Torque-limits were also greater for humans compared with cats. Scaling relationships with high correlation ( R 2 greater than 0.77) were established during later LB and AR. Conclusions The current study defined “physiological ranges of movement” for human and cat lumbar spine specimens during displacement-controlled testing, and should be observed in future biomechanical studies conducted under displacement control.