Comparison of mechanical and histological properties between the immature and mature tendon attachment

We tested the tensile strength of the Achilles tendon attachment to the calcaneus in skeletal mature and immature rabbits. The mean ultimate failure load was 179.6+/-28.6 N in the mature animals, and 138.5+/-36.1 N in the immature animals ( P<0.05). Although direct insertion was clearly observed histologically in the mature animals, direct insertion was not obvious in the immature animals. In the mature animals, failure occurred partly at the attachment zone (50%) and partly at the tendon zone (50%). In the immature animals, failure occurred at the attachment zone in 85% and at the tendon zone in 15%.