Growth related increase in an intervertebral disc space in rats.

Methods have been developed that permit repetitive radiographic measurement of the lumbar L4-5 intervertebral disc space area in the laboratory rat. In using this approach, the coefficient of variation in repetitive determinations was 7.6 +/- 0.7%. Normal rats have been shown to manifest statistically significant increase in disc space area size between 2.5 and 5 months of age.