Augmentation Of Tendon-bone Healing With Calcium-phosphate Cement

Object: to research effect of normal CPC and rhBMP2-CPC on the healing of bone and tendon after semitendinous autograft reconstructions of the anterior cruciate ligament .Methods: semitendinous autograft reconstructions of the anterior cruciate ligament were performed on both knees of 36 New Zealand white rabbits which been divided to ABC three groups at random. The semitendinosus tendon was chosen for reconstruction of the anterior cruciate ligament(ACL) because of its uniformity of size and length.1 After the rabbits had been anaesthetized with intravenous Nembutal (26ml/kg), an anteromedial incision was made through the medial retinaculum. The ACL was excised and a bone tunnel, with a diameter of 2.4 mm, was made in the proximal tibia just anterior to the medial collateral ligament (MCL) ending at the original point of insertion of the ACL on the intercondylar tibial spine. A femoral tunnel of the same size was made from the midline of the intercondylar notch ending just superior to the origin of the lateral collateral ligament (LCL). The semitendinosus tendon was dissected and passed through the tibial and femoral bone tunnels and sutured to the LCL. The procedure was repeated for the other knee. In group A , the interface between the grafted tendon and the femoral bone tunnel was filled with 0.5 ml of rhBMP2-CPC injected into the interface from a 2 ml syringe with a 19-gauge needle through the extrusion orifice of the femoral bone tunnel. In group B, the interface between the grafted tendon and the femoral bone tunnel was filled with 0.5 ml of normal CPC injected into the interface from a 2 ml syringe with a 19-gauge needle through the extrusion orifice of the femoral bone tunnel. The interface between the grafted tendon and the bone tunnel for C group were filled with nothing. After operations, using histological observation of tissue and biomechanical methods to evaluate the tendon-bone healing. The mechanics testing machine model CSS-44020 featuring a 50 kg load cell was used to detect the maximal tensile strength of the healing tissue. The test samples were dissected to the level of a bone tendon bone model, the bones of which were mounted at each end of the tubular mounts with cross pins and resin. The femur was fixed at 45°of flexion in order to align the bone tunnel along the direction of the testing force. Before beginning the stress loading, the suture fixing the grafted tendon to the LCL was removed so that the interface tissue would be the only material to be exposed to the pulling force. The original attachment of the grafted semitendinosus tendon to the tibia was allowed to remain. It was anticipated that the failure point would be situated at the site of the femoral bone tunnel. The tensile force was applied at a rate of displacement of 5.0 mm/s until the point was reached at which the tendon was pulled out of the femoral bone tunnel. The maximal level of tensile strength corresponding to this point was thus determined and the data were analysed statistically by the Wilcoxon signed-rank test.Results: Histological and gross findings. One-week specimens. Histological examination of the rhBMP2-CPC group showed that most of the tendon-bone interface was filled with chondrocytes, although thin layers of fibrous tissue were observed between CPC fragments and adjacent to the surface of both the grafted tendon and the bone tunnel. In the B group, there was a part of chondrocytes in the interface .In the group C, there was a collection of loose tissue in the interface consisting mainly of fibrous tissue. Three-week specimens. Histological examination showedmany growing bone islands within the material some of which had formed directly on the surface of the bone and the tendon in group A. There appeared to be a continuity between the bone and tendon. And there were some growing bone islands within the material in group B. The healing tissue of the C group showed an increased production of extracellular collagen fibres which were distributed in a circular orientation around the grafted tendon. Those adjacent to the grafted tendon had an irregular orientation and were interwoven with the fibres of the grafted tendon. Collagen fibres attached to the bone tunnel were observed only occasionally.Six-week specimens. Histological examination showed that the interface between the bone tunnel and grafted tendon was almost filled by new bone in group A. The fibres of the grafted tendon appeared to be firmly anchored onto the new growing bone. Some portions of the collagen fibres in the interface had matured to become organised into bundles. the interface between the bone tunnel and grafted tendon was filled by some new bone in group B. however, in group C, the interface between the bone tunnel and grafted tendon was just filled by Collagen fibres.Twelve-week specimens. Histological examination showed that most portions of the bone-tendon interface appeared to have been filled by new bone. Continuity between the collagen fibres of the grafted tendon and surrounding bone was seen in group A. In the group B, a lot of new bone was seen in the interfacial gap. In the group C, a part of new bone was seen in the interfacial gap.Conclusion: calcium-phosphate cement can augmentate the early tendon-bone healing. Especially, the effect of rhBMP2-CPC were distinctness.