Healing of bone-tendon junction in a bone trough: a goat partial patellectomy model.

Bone-tendon junction healing in a bone trough was investigated in a goat partial patellectomy model. Histologic evaluation and biomechanical tests were done at 6, 12, and 24 weeks. Irregular fibrous tissue seen at the healing bone-tendon junction at 6 weeks gradually assumed longitudinal alignment and remodeled toward a direct bone-tendon junction. Type III collagen deposition was diffuse at 6 weeks, but became localized to the healing interface at 12 weeks. Thickness of newly formed bone increased progressively with time. Bridging collagen fibers were formed at the junction, with fibrochondrocytic cells and a basophilic tidemark detected at 24 weeks. The trabecular line remained discontinuous and there was no safranin O uptake. Most specimens failed at the junctions under tensile loads. The ultimate failure stress increased from 4.78 +/- 0.50 N/mm2 at 6 weeks to 7.99 +/- 0.33 N/mm2 at 24 weeks (mean +/- standard error of the mean), only reaching 15% of normal. Cartilage from the articular cut surface extended into the healing interface, later forming an area of fibrocartilage with densely packed collagen fibers aligned along the direction of force, containing proteoglycans. Cartilage may enhance restoration of a transition zone in bone-tendon junction healing. The sequence of events outlined formed a basis to guide clinical practice regarding bone-tendon junction reattachment.