Patellar Tendon-to-Bone Healing Using High-Density Collagen Bone Anchor at 4 Years in a Sheep Model

Abstract

Background This study reports the long-term histologic and mechanical properties of the healing patellar tendon–bone interface reconstructed using a high-density type I collagen bone anchor (HDC) compared to a metal anchor in sheep. Hypothesis To determine the long-term histology and mechanical properties of extra-articular tendon-bone healing and in vivo response to a HDC anchor. Study Design Controlled laboratory study. Methods The structural properties, tendon-bone histology, and device histology in the bone were examined out to 208 weeks in a sheep model. Results The patellar tendon–proximal tibia bone interface continued to remodel with time but, by 4 years, had yet to develop the well-defined zones of tendon, fibrocartilage, calcified cartilage, and bone of the native patellar tendon to bone insertion. The insertion repair strength did not vary between the repaired tendons and the nonoperated controls at any time. Conclusion The healing tendon-bone interface undergoes a gradual remodeling process, which had yet to reconstitute back to the control interface by 208 weeks. The HDC device remained essentially intact at 208 weeks showing little signs of degradation. Clinical Relevance Tendon-bone healing is mechanically equivalent to the contralateral side by 26 weeks whereas histologic structure requires much longer to remodel back to the native insertion.