In double-bundle anterior cruciate ligament reconstruction, even though overall forces in the graft are the same as intact anterior cruciate ligament, the force distributions may not be the same as the intact bundles, and overloading of 1 of the 2 grafts may occur.

For years, bioengineers and orthopaedic surgeons have applied the principles of mechanics to gain valuable information about the complex function of the anterior cruciate ligament (ACL). The results of these investigations have provided scientific data for surgeons to improve methods of ACL reconstruction and postoperative rehabilitation. This review paper will present specific examples of how the field of biomechanics has impacted the evolution of ACL research. The anatomy and biomechanics of the ACL as well as the discovery of new tools in ACL-related biomechanical study are first introduced. Some important factors affecting the surgical outcome of ACL reconstruction, including graft selection, tunnel placement, initial graft tension, graft fixation, graft tunnel motion and healing, are then discussed. The scientific basis for the new surgical procedure, i.e., anatomic double bundle ACL reconstruction, designed to regain rotatory stability of the knee, is presented. To conclude, the future role of biomechanics in gaining valuable in-vivo data that can further advance the understanding of the ACL and ACL graft function in order to improve the patient outcome following ACL reconstruction is suggested.

A range of knee flexion angles that is safe for the fixation of both grafts in double-bundle anterior cruciate ligament reconstruction was determined.

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ABSTRACT:The two functional bundles of the anterior cruciate ligament (ACL), namely, the anteromedial (AM) and posterolateral (PL) bundles, must work in concert to control displacement of the tibia relative to the femur for complex motions. Thus, the replacement graft(s) for a torn ACL should possess similar tension patterns. The objective of the study was to examine whether a double-bundle ACL reconstruction with the semitendinosus-gracilis autografts could replicate the tension patterns of those for the intact ACL under controlled in vitro loading conditions. By means of a robotic/universal force moment sensor (UFS) testing system, the in situ force vectors (both magnitude and direction) for the AM and PL bundles of the ACL, as well as their respective replacement grafts, were determined and compared on nine human cadaveric knees. It was found that double-bundle ACL reconstruction could closely replicate the in situ force vectors. Under a 134-N anterior tibial load, the resultant force vectors for the intact ACL and the reconstructed ACL had a difference of 5 to 11 N (p > 0.05) in magnitude and 1 to 138 (p > 0.05) in direction. Whereas, under combined rotatory loads of 10-N-m valgus and 5-N-m internal tibial torques, the corresponding differences were 10 to 16 N and 48 to 118, respectively. Again, there were no statistically significant differences except at 308 of flexion where the force vector for the AM graft had a 158 (p < 0.05) lower elevation angle than did the AM bundle. The anterior cruciate ligament (ACL) is one of the major stabilizers of the knee joint, providing restraint to anterior tibial translation as well as to varus-valgus and axial tibial rotations. It has an irregular cross-sectional shape along its length and can be anatomically divided into two functional bundles, namely, the anteromedial (AM) and the posterolateral (PL) bundles, 1,2 each playing different roles in stabilizing the knee joint. When the knee is extended, both bundles are taut. As the knee is flexed, the AM bundle further tightens and the PL bundle becomes relatively lax. Biomechanical studies have further revealed that under an applied anterior tibial load, the PL bundle shares the load with the AM bundle near full knee extension; whereas, the AM bundle carries more load as knee flexion angle increases. 3As a major knee stabilizer, the ACL is also the most frequently injured ligament during sports activities, 4,5 such as basketball, skiing, soccer, and football. A torn ACL may result in knee instability if left untreated. Due to its poor healing capability, surgeons often perform ACL reconstruction using replacement tissue grafts. Recently, the literature has shown that under controlled in vitro tests simulating clinical exams (e.g., anterior tibial drawer/Lachman test and pivot shift test), these procedures which were designed chiefly to replace only the AM bundle can successfully limit anterior tibial translation under anterior tibial load, but become insufficient under rotator loads. 6,7 These findings have contributed t...