Tendon-Bone Healing Enhancement Using Injectable Tricalcium Phosphate in a Dog Anterior Cruciate Ligament Reconstruction Model

Purpose: The purpose of this study was to evaluate the enhancement potential of injectable tricalcium phosphate (TCP) for tendon-bone healing in anterior cruciate ligament (ACL) reconstruction in a dog model. Methods: In this experimental study ACL reconstruction was performed on both knees of 48 beagle dogs with the tendon of the flexor digitorum longus. A suspension fixation technique was used, and the tendon graft filled only the tunnel parts near the joint. On the experimental side, in addition to ACL reconstruction, injectable TCP was used to fill those tunnel parts that were not filled by the graft. On the other side, no additional treatment was applied (control). At 2, 4, 6, 8, 10, and 12 weeks postoperatively, 8 dogs were killed, respectively, with 3 for histologic observation at the proximal tendon-bone junction and 5 for mechanical examination. Results: Histologic observation showed that on the experimental side, Sharpey fibers, fibrocartilage, and calcified cartilage appear earlier at the tendon-bone interface and tendon-bone healing proceeded more quickly than on the control side. Mechanical examination showed that within 4 weeks, the pullout strength was higher on the experimental side than on the control side, and there was a statistically significant difference between the results. Conclusions: Filling the bone tunnel with TCP after inserting the ACL graft results in faster incorporation of the graft to the tunnel, with better biomechanical properties and a more mature histologic pattern. Clinical Relevance: If these results are clinically applicable, rapid tendon-bone healing may be expected in ACL reconstruction.