Tendon growth in rabbits.

The longitudinal growth of the Achilles and tibialis anterior tendons in young rabbits was investigated. At 5 weeks of age, sutured marks were placed along the entire length of each tendon from the musculotendinous junction to the portion near the osseous attachment using a microsurgical technique. The distances between the marks were measured using a microscope with a micro ruler. At 16 weeks of age, all distances between the marks had increased. In the Achilles tendon, none of the intermark distances differed significantly. In the tibialis anterior, the retinaculum is situated between the musculotendinous junction and the insertion, and acts as a pulley, so this tendon was divided into 2 zones, one proximal and one distal to the retinaculum, and the intermark distances were measured. There were no significant differences among these distances in proximal, or distal zones, but those in the proximal zone were greater than those in the distal zone (< 0.01). Furthermore, in a separate experiment, the longitudinal growth of the underlying bone in the zone proximal to the retinaculum was found to be greater than that in the distal zone (p < 0.01).