Biomechanical evaluation of the New Zealand white rabbit lumbar spine: a physiologic characterization

Physiologic motions of the human, sheep, and calf lumbar spines have been w ell characterized. The size, cost, and ease of care all make the rabbit an attractive alternative choice for an animal lumbar spine model. However, co mparisons of normal biomechanical characteristics of the rabbit lumbar spin e have not been made to the spines of larger species. The purpose of this s tudy was to establish baseline physiologic kinematic data fur the rabbit lu mbar spine. Ten skeletally mature New Zealand white rabbit osteoligamentous spines were obtained. L4-L7 spine segments were harvested and mounted. Mul ti-directional flexibility testing was performed by applying pure moments u p to 0.27 Nm. Resulting rotations were measured using an Optotrak system. D ata were analyzed for each intervertebral level in the three planes of rota tion. The three levels tested had roughly similar range of motion (ROM). Th e mean (SD) angular ROMs in flexion fur L4-L5, L5-L6, L6-L7 were 12.10 degr ees (2.59 degrees), 12.38 degrees (2.70 degrees), and 15.17 degrees (3.22 d egrees), respectively. The ROMs in extension were 5.86 degrees (1.21 degree s), 5.58 degrees (1.48 degrees), and 6.13 degrees (2.03 degrees). Lateral b ending and axial rotation were roughly symmetric due to the symmetric natur e of the spine. For right lateral bending, the ROMs were 8.25 degrees (2.44 degrees), 4.96 degrees (1.70 degrees), and 4.25 degrees (1.20 degrees). Fo r left axial rotation, the ROMs were 1.23 degrees (1.16 degrees), 0.35 degr ees (0.61 degrees), 0.87 degrees (0.64 degrees). Neutral zone (NZ) was on a verage 60% (29%) of ROM fur the motions studied. The physiologic ROM of the New Zealand white rabbit lumbar spine was found to be similar between the rabbit and human. This relatively conserved physiologic flexibility support s the use of the rabbit as a model of the lumbar spine for kinematic studie s. However, the overall NZ was found to be a greater percentage of ROM in t he rabbit than the corresponding percentage in the human (60% as compared t o 25%). This suggested that the rabbit lumbar spine has a greater laxity th an that of the human.