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The influence of the gap size on the interfacial union between the bone and the tendon.

An in-vivo model of New Zealand white rabbit was used to study the influence of gap size on the interfacial union between bone and tendon through histological observation and mechanical testing. In the model, the anterior cruciate ligament (ACL) was cut and reconstructed by autografted semitendinosus tendon (with average diameter of 1.48 mm +/- 0.12 mm). Mechanical testing of the interfacial healing tissue was done on the 15th post-operative day. At that time the mean maximal tensile strength was 2.511 +/- 0.293 kg to a bone tunnel size of 1.5 mm. The maximal tensile strength lowered to 1.853 +/- 0.563 kg to a bone tunnel size of 1.8 mm. The maximal tensile strength lowered to 1.302 +/- 0.657 kg to a bone tunnel size of 2.0 mm. Using a paired-t test, the gap size was found to have great influence on the tensile strength of the interfacial healing tissue (p < 0.05). The histological study showed that the interfacial gap was connected by the new growing collagen fibers. The healing tissue appeared much denser and much more maturated and organized in the smaller interfacial gap in comparison with specimens with a larger gap so that it can tolerate higher tensile strength. From this study, we concluded that the gap size really plays an important role in the process of maturation and organization of interfacial healing tissue. Furthermore, we recommend that in order to achieve greater anchoring strength of the grafted tendons, the bone tunnel should be made with approximately the same diameter of grafted tendon.