Biomechanical evaluation of patellar and hamstring tendon graft fixation for anterior cruciate ligament reconstruction using a poly-(D,L-lactide) interference screw

Anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendons are being performed more frequently and satisfactory results have b een reported. Advantages such as low donor site morbidity and ease of harve st as well as disadvantages like low initial construct stiffness have been described. Recently, it has been demonstrated that graft fixation close to the original ACL insertion sites increases anterior knee stability and graf t isometry. Hamstring tendon fixation techniques using interference screws offer this possibility. To reduce the risk of graft laceration, a round thr eaded titanium interference screw (RCI) was developed. To improve initial f ixation strength, fixation techniques for hamstring tendons with separate o r attached tibial bone plugs were introduced. However, data on fixation str ength do not yet exist. With respect to the proposed advantages of biodegra dable implants, like undistorted magnetic resonance imaging, uncompromised revision surgery and a decreased potential of graft laceration during screw insertion, we performed pullout tests of round threaded biodegradable and round threaded titanium interference screw fixation of semitendinosus (ST) grafts with and without distally attached tibial bone plugs. Data were comp ared with bone-tendon-bone (BTB) graft fixation using biodegradable and con ventional titanium interference screws. We used 56 proximal calf tibiae to compare maximum pullout force screw inse rtion torque, and stiffness of fixation for biodegradable direct ST tendon and bone plug fixation (group I: without bone plug, group II: with bone plu g) versus titanium interference screw fixation (group III: without bone plu g, group IV: with bone plug). A round threaded biodegradable poly-(D,L-lact ide) (Sysorb) and a round threaded titanium interference screw (RCI) were u sed. As a control calf bone-tendon-bone (BTB) grafts fixed with either poly -(D,L-lactide) (group V) or conventional titanium (group VI) interference s crews were used. ST tendons were harvested either with or without their dis tally attached tibial bone plugs from human cadavers and were folded to a t hree-stranded graft. Specimen were loaded in a material testing machine wit h the applied load parallel to the long axis of the bone tunnel. Maximum pullout force of ST bone plug (group III: 717 N +/- 90, group IV: 6 02 N +/- 117) fixation was significantly higher than that of direct tendon (group I: 507 N +/- 93, group III: 419 N +/- 77) fixation. Maximum pullout force of biodegradable screw ST fixation was higher than that of titanium s crew fixation in both settings. There was no significant difference in pull out force between biodegradable (713 N + 210) and titanium (822 N +/- 130) BTB graft fixation or between ST fixation with bone plug and biodegradable screw with BTB fixation. Pullout force of hamstring tendon interference screw fixation can be improv ed by using a biodegradable implant. In addition, initial pullout force can be greatly improved by harvesting the hamstring tendon graft with its dist ally attached tibial bone plug. This may be important, especially in improv ing tibial graft fixation. This study encourages further research in tendon -bone healing with direct interference screw fixation to confirm the potent ial of this advanced method.