Abstract des Autors

Disruption of the anterior cruciate ligament (ACL) has been shown to lead to early onset of osteoarthritis. Although ACL reconstruction is commonly performed, the degenerative changes continue despite surgery. One of the primary variables that influence the outcome of surgical reconstruction is post-operative rehabilitation. It is through rehabilitation that the mechanical strain environment of the ACL graft is controlled to optimize healing. Thus, there is a need to understand the strain response of the ACL, particularly its response to muscle function and weightbearing. Since knee joint stability is maintained through a force balance between the ligaments, articular contact, musculature and bodyweight, our approach has been to study ACL biomechanics in vivo. The objective of this paper is to review our recent data and to provide a comprehensive understanding of the ACL and how it interacts with the leg musculature. The Differential Variable Reluctance Transducer (DVRT) was used to measure the ACL strain behavior during passive loading conditions (muscles inactive), activation of the quadriceps, hamstrings, and gastrocnemius muscles, weightbearing, and commonly prescribed rehabilitation activities. We revealed that the ACL is a primary restraint to anterior loading and internal torque (tibia relative to femur) but not to external torque, varus, or valgus moments applied to the knee when in the non-weightbearing state. Isolated quadriceps contractions strained the ACL when the knee was between 50ø and full extension and isolated hamstrings contractions did not strain the ACL over the entire range of knee motion. Co-contraction of the quadriceps and hamstring muscles reduced ACL strain values compared to isolated contractions of the quadriceps but it did not eliminate the strains when the knee was at 30ø to extension. Likewise, isolated contractions of the gastrocnemius muscle also strained the ACL when the knee was flexed at 30ø to extension. Another important finding was the increase in ACL strain values that occurred as the knee transitioned from non-weightbearing to weightbearing, questioning the popular belief that compressive loading of the knee protects a healing ACL graft. The strains produced during weightbearing and muscle co-contraction also play a role in the analysis of different rehabilitation exercises. Closed kinetic chain exercises are commonly prescribed following ACL reconstruction since they involve quadriceps and hamstring muscle co-contraction and maintain the compressive load produced by bodyweight to protect the ACL. However, a comparison between maximum strain values produced during an open kinetic chain exercise (active knee extension) versus squatting demonstrated that there was no significant difference. This finding indicates that the closed- and open-kinetic chain terminology may not be appropriate for the rehabilitation of ACL grafts. These data provide a foundation on which clinical investigations can be designed and implemented to optimize ACL graft healing. Verf.-Referat