The Development and Biomechanical Study of Ligament Anchor Screw

Song, Eun Kyoo; Lee, Keun Bae; Jung, Sung Taek; Bae, Bong Hyun

Abstract

Various methods for fixation of grafts have been used in the reconstruction of the anterior cruciate ligament (ACL). However, the biomechanical strength of each of the fixation devices have not been fully investigated. The Ligament Anchor(LA) screw is a new device designed for ACL reconstruction using hamstring tendon. The Ligament Anchor screw has screw threads on the head portion for fixation into the distal femur and an eyelet on the tail portion for anchorage of the tendon. The purpose of this study is to compare the maximum tensile strength at failure of the Ligament Anchor screw with other fixation devices for ACL reconstruction, which is the most important factor for the success at the initial stage of healing. The bone-patellar tendon-bone (BPTB) and hamstring (hind hoof extensor) tendons were fixed in the femoral tunnel of Yorkshire pig knees by different surgical techniques; Ligament Anchor screw, Interference screw fixation (titanium and biodegradable), SemiFix screw and the Endobutton technique. Six groups were made and their maximum tensile strength at failure were measured by an Instron tensometer. The failure modes were also observed. ANOVA and Duncan multiple comparison tests were applied for statistical analysis, as appropriate. The mean maximum tensile strength of the group of hamstring fixed by the Ligament Anchor screw (1251.6+/-145.2N), SemiFix screw (1405.9+/-135.1N), BPTB graft fixed by the titanium (1333.4+/-148.5N) and biodegradable interference screw (1310.1+/-168.9N) were statistically higher than the other two groups, by biodegradable interference screw (820.3+/-104.5N) and Endobutton (682.1+/-54.2N) with hamstring (p<0.05). Ligament Anchor screw failure modes were characterized by pull-out of the screw from the femoral tunnel in all cases. In cases of hamstring graft fixed by biodegradable screw, tendons were pulled-out from the femoral tunnel while the screw remained in place. Bending of screws and the rupture of polyester tape were observed in the cases using the SemiFix screw and the Endobutton technique. In the groups of BPTB graft fixed by titanium and biodegradable screws, the pulled-out of the bone plug from the femoral tunnel without any change of position of the screw was observed in most cases. Application of the Ligament Anchor screw for ACL reconstruction using hamstring tendon is a favorable method for its stability, ease, simplicity, and reliability.