The New Zealand White Rabbit as a Kinematic Model of the Human Lumbar Spine

Jonathan S. Erulkar BA
Jonathan N. Grauer, MD
Tushar Ch. Patel, MD
Manohar M. Panjabi, PhD (New Haven, CT)

The size, cost, and ease of care all make the rabbit an attractive choice for an animal spine model. Previous and on–going research investigating bone morphogenetic proteins as a potential substitute for autograft in lumbar fusions have already utilized the rabbit model. Nevertheless, comparisons of normal biomechanical properties of the rabbit and human lumbar spine have not yet been made.

Ten skeletally mature rabbit osteoligamentous spines were obtained. L4–7 segments were harvested and multidirectional flexibility testing was performed. Resulting rotations were measured using an Optotrak system, and data were analyzed for each intervertebral level in the three planes of motion.

The mean (SD) angular range of motions (ROMs) in flexion for L4–5, L5–6 and L6–7 were 12.10o (2.59o), 12.38o (2.70o), and 15.17o (3.22o), respectively. The ROMs in extension were 5.86o (1.21o), 5.58o (1.48o), and 6.13o (2.03o). Right lateral bending ROMs were 8.25o (2.44o), 4.96o (1.70o) and 4.25o (1.20o). Left axial rotation ROMs were 1.23o (1.16o), 0.35o (0.61o), and 0.87o (0.64o). Neutral zone (NZ) was on average 60% (29%) of ROM for the motions studied.

The physiologic ROM data were remarkably similar between the rabbit and the human. The average difference in ROM between the two species at the levels studied was only 2.42o (1.83o). The conserved physiologic flexibility between the two species supports the use of the rabbit as a model of the lumbar spine for kinematic studies.