By Jordana Bieze Foster
Exercises prescribed for rehabilitation after anterior cruciate ligament (ACL) reconstruction should be designed to protect the healing graft from excessive strain in addition to rebuilding muscle strength and activation, according to evidence-based recommendations from a multicenter team of experts.
The guide to exercise selection, published this month in the Journal of Orthopaedic & Sports Physical Therapy, reviews the existing literature on how specific exercises affect ACL loading and provides scientific support for rehabilitation strategies many practitioners are already using.
“I believe our recommendations are being used in varying degrees by clinicians rehabbing ACL patients,” said Rafael Escamilla, PhD, PT, CSCS, professor of physical therapy at California State University, Sacramento, and lead author of the article.
The exercises in question are those in which the knee is loaded while flexed, including squats, lunges, leg press, seated leg extension, and seated knee flexion—all of which are effective for improving strength and activation in the muscles surrounding and supporting the reconstructed knee.
Escamilla and colleagues’ review of the literature suggests that loading on the ACL is greatest at low flexion angles (10° to 50°) and peaks between 10° and 30° of flexion. Studies also suggest that weightbearing exercises are associated with significantly lower levels of ACL strain than nonweightbearing exercises, particularly seated knee extensions.
However, particularly in the early period after ACL reconstruction, patients may not be able to bear weight easily and may not be able to achieve greater knee flexion angles because of pain, swelling, or limited range of motion. Because this early period is also when the graft is most vulnerable, practitioners may want to opt for partial-weight adaptations of traditional weightbearing exercises, such as minisquats and lunges performed from 0° to 45° of flexion, then gradually have patients progress to full weightbearing and 0° to 90° of flexion.
Once patients achieve greater ranges of motion, weightbearing leg press exercises can be safely performed without loading the ACL. Seated knee extensions can eventually be introduced between 50° and 100° of knee flexion.
“In general, the initial four to eight weeks are the most crucial,” Escamilla said.
The recommendations also note evidence that ACL loading can be reduced by facilitating hamstring contraction with body positioning. Athletes can flex the hips to achieve a forward trunk tilt of 30° to 40° during squatting or lunging, or they can keep the knees from moving forward more than 8 cm to 10 cm beyond the toes during squats. Correct limb alignment during all exercises is essential.
The type of graft used in ACL reconstruction can be another important consideration in exercise selection in the early weeks after surgery. Few studies have analyzed the loading effects of different rehabilitation exercises on different graft types. However, research demonstrating longer incorporation times for ACL allografts than autografts suggests that a conservative rehabilitation approach is warranted following allograft surgery.
The medical literature does offer some guidance regarding hamstring autografts, particularly with respect to resisted knee flexion exercises. The recommendations support seated resisted knee flexion exercises for early rehabilitation if a bone-patellar tendon-bone graft was used, because such research suggests such exercises create very little load on the ACL. But if a hamstring autograft was used, practitioners should avoid resisted knee flexion because the exercise stresses the semitendinosus muscle, which can impair healing at the graft harvest site. Isometric knee flexion exercises can begin about six weeks after surgery, and dynamic knee flexion exercises about two weeks later; between weeks eight and 12 hamstring exercises should be performed in the patient’s pain-free range of motion, typically 0° to 90°.
Once the patient has progressed from early graft healing to the intermediate stages of rehabilitation, ACL loading can be gradually increased.
Escamilla RF, MacLeod TD, Wilk KE, et al. Anterior cruciate ligament strain and tensile forces for weight-bearing and non-weight-bearing exercises: A guide to exercise selection. J Orthop Sports Phys Ther 2012;42(3):208-220.