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ACL injuries: causes, identification, treatments

This is an excerpt from Sports Injuries Guidebook by Robert Gotlin.

Anterior Cruciate Ligament Tear

Common Causes

Rupture of the anterior cruciate ligament (ACL) occurs more often in females than in males, from adolescents to older adults. Noncontact injuries to the knee are responsible for most ACL tears. Pivoting and cutting sports (soccer and basketball) are the most common scenarios for noncontact ACL injuries, whereas most direct contact ACL injuries occur in American football. ACL tears can be associated with meniscal tears or collateral ligament injuries.


Most athletes who have torn their ACL will hear or feel a pop accompanied by pain and, soon after, swelling, though in rare cases little swelling occurs. Rapid swelling in the knee is typically caused by bleeding associated with the injury. The pain might subside quickly after an ACL injury, but this does not mean the tear or strain is healing. An athlete will experience instability with an insecure sensation while pivoting or loading the knee; an occasional sense of hyperextension of the knee is also common. Tenderness often occurs at the lateral joint line.

Critical to diagnosis of the ACL tear is the Lachman test, which evaluates the ACL laxity at 30 degrees of knee flexion and includes the uninjured knee for comparison. If the ligament is intact, there will be an endpoint feeling like tensing a string. Absence of this firm sensation typically signals an ACL tear. The medial, lateral, and posterior ligaments are tested as well. Evaluating range of motion is especially important. Standard X-rays are required but seldom reveal much. Occasionally, a small piece of bone that has pulled off of the lateral aspect of the tibia might show up on X-ray. This indicates an avulsion fracture and is typically associated with an ACL tear. MRI is quite accurate in diagnosing ACL tears. Typically, MRI findings with a torn ACL include bone bruises at the end of the thigh bone, femur, and posterior tibia; swelling; and an abnormal ACL at the femoral attachment. It is not uncommon to
have an associated meniscal injury with an ACL tear, and this is also diagnosed with MRI.


Age, occupation, desired activity, sports involvement, and associated injuries to the knee are all taken into consideration when deciding on treatment for an ACL tear. Nonoperative treatment includes supervised physical therapy to restore range of motion, decrease swelling, and restore strength. With return to activities, athletes in more vigorous sports might use a derotational ACL brace.

Thanks to recent advances in arthroscopic ACL reconstructive procedures and more rapid postop recovery and return to sports, surgery for ACL tears is a much more attractive option than it once was. In the very young patient with open growth plates, surgery might be delayed until bone maturation, but there is some controversy about this. In the patient older than 60 years, nonoperative treatment is generally recommended but certainly the octagenerian who skis on a regular basis may opt for surgical reconstruction of the ACL. Whereas nonoperative treatment might be considered in any age group for isolated ACL injuries, it is typically less successful in active and athletic patients.

Postsurgery, athletes typically return to school or sedentary work within a week. Athletes will use crutches for one to two weeks and begin physical therapy almost immediately. Physical therapy and a strengthening program continue until the injured knee has 90 percent of the strength of the other knee. Training focuses on strengthening the hamstring and quadriceps muscle groups as well as the other lower extremities. The hamstring muscles are particularly important because they add stability to the injured knee. Hamstring contractions pull the tibia backward, which helps counter the inherent ACL instability, which is a forward glide of the tibia. Also, full-knee extension is critical for long-term knee function and should always be a priority in treatment. Clinical results of ACL reconstruction are quite good, with very low reinjury rates. The most common complication is some residual anterior knee pain. Strengthening the hip muscles during therapy is also extremely important in helping to restore stability in the lower limbs and decrease strain on the reconstructed ligament.

Return to Action

With surgery and rehab, athletes can usually return to sport in about six months. Bracing might be initially beneficial upon return. The decision to brace usually depends on athlete preference and whether any instability remains in the rehabilitated knee. Some medical professionals evaluate the post-ACL athlete via a series of functional tests to assess the knee's strength and stability. Devices such as isokinetic strength-testing machines and a series of hopping tests are used. Athletes must progress slowly in resuming sport activity and perform exercises such as running, cutting, twisting, and jumping to mimic the movements of the sport before beginning full participation.

This is an excerpt from Sports Injuries Guidebook.

More Excerpts From Sports Injuries Guidebook