Effects of collagen gel mixed with hydroxyapatite powder on interface between newly formed bone and grafted achilles tendon in rabbit femoral bone tunnel.

The Achilles tendon was implanted into a bone tunnel made in the femoral condyle of 20 rabbits. In the left femur, collagen gel mixed with hydroxyapatite powder (C-HAp) was injected between the graft and the bone tunnel. On the other hand, as a control, simple saline was injected in the right femur. Five rabbits were sacrificed at 4, 8, 12, and 16 weeks after surgery. Histological findings showed that in the C-HAp group, the grafted tendon came in direct contact with new bone, and Sharpey-like collagen fibers arising from the grafted tendon were observed to penetrate new bone by 4 weeks after surgery. In the control group, however, fibrous tissue was observed between new bone and the grafted tendon, but no penetrating fibers from the grafted tendon into the new bone were observed until 16 weeks. The area of new bone in the C-HAp group was significantly greater than that in the control group 4, 8, and 12 weeks after surgery (p < 0.0001, p < 0.0007, p < 0.0013, respectively).