Firm anchoring between a calcium phosphate-hybridized tendon and bone for anterior cruciate ligament reconstruction in a goat model

Using an alternative soaking process improved the tendon–bone attachment for a calcium phosphate (CaP)-hybridized tendon graft. We characterized the deposited CaP on and in tendons and analyzed the histology and mechanical properties of the tendon–bone interface in anterior cruciate ligament (ACL) reconstruction in goats. The tendon grafts to be implanted were soaked ten times alternately in a Ca-containing solution and a PO4-containing solution for 30 s each. Needlelike CaP nanocrystals including low-crystalline apatite were deposited on and between collagen fibrils from the surface to a depth of 200 µm inside the tendon. The structure resembles the extracellular matrix of bone. In animal experiments, the CaP-hybridized tendon directly bonded with newly formed bone at 6 weeks (n = 3), while fibrous bonding was observed in the control (n = 3). The ultimate failure load was not statistically different between the CaP (n = 7) and control (n = 7). However, in the failure mode, all the tendon–bone interfaces were intact in the CaP group, while three of seven specimens were pulled out from bone tunnels in the control. The result suggested that the strength of the tendon–bone interface in the CaP group is superior to that in the control group. Clinically, firm tendon–bone anchoring may lead to good results without the knee instability associated with the loosening of the bone–tendon junction in ACL reconstruction.