Knee ligament injuries

Knee injuries in general, including ligament and meniscal injuries and patellar fractures, are common injuries.

The anterior cruciate ligament (ACL) prevents anterior translation of the tibia, tibial rotation, and valgus/varus displacement. The ACL is the most commonly injured knee ligament, accounting for approximately half of all knee injuries. It’s more common among females.

The posterior cruciate ligament (PCL) is the largest and strongest intra-articular ligament of the knee. It prevents posterior translation of the tibia. The medial collateral ligament (MCL) prevents valgus stress and tibial rotation. The lateral collateral ligament (LCL) prevents varus stress and tibial rotation. Isolated LCL injury is rare.

The “unhappy triad” refers to simultaneous injury of the ACL, MCL, and medial meniscus.

Etiology

ACL injury occurs mostly due to external rotation (twisting) of the knee during sports. It may also occur due to high energy trauma due to forced hyperextension of the knee.

PCL injury occurs due to forced hyperflexion with plantarflexed foot, often occurring during sports. It may also occur due to high energy trauma due to blow to a flexed knee.

MCL injury occurs due to valgus stress to the knee.

Osteophytes from osteoarthritis may predispose to ligament injury as the osteophytes can damage the ligament.

Clinical features

Symptoms include knee instability when walking, pain, and swelling (may be due to haemarthrosis from bleeding from the ligament). Swelling occurs immediately in ACL injuries. The patient reporting hearing a “pop”, “cracking” or “crunching” sound is suspicious for a ligament injury.

PCL, MCL, and LCL injury causes less symptoms than ACL injury.

Diagnosis and evaluation

Many physical examination manoeuvres are used in the evaluation of knee ligament injuries.

The valgus stress test involves applying valgus stress to the knee (by pushing medially) while the knee is in extension and 20 – 30° flexion. Widening of the joint space, felt as medial laxity, indicates MCL, ACL, or posteromedial capsule injury.

The varus stress test involves applying varus stress to the knee (by pushing lateral) while the knee is in extension and 20 – 30° flexion. Widening of the joint space, felt as lateral laxity, indicates LCL, ACL, or posterolateral capsule injury.

Lachman test involves having the patient’s knee in light flexion (15 – 20°), gripping the upper part of the tibia with one hand and the lower part of the femur with the other, and attempting to “pull” the tibia anteriorly. If the tibia can be pulled 3 – 4 mm anteriorly (anterior tibial translation, compare with the other side), the test is positive and indicates ACL injury. Lachman test is superior to the drawer test for diagnosing ACL injuries.

Anterior-posterior drawer test is similar to Lachman test. The patient’s knee is in 90° flexion, and the examiner fixes the patient’s foot on the table and attempts to pull the proximal tibia anteriorly and push it posteriorly. Anterior laxity (translation) indicates ACL injury, while posterior laxity indicates PCL injury.

The patella dip test may be used to demonstrate intraarticular fluid (not only in ligament injuries), including haemarthrosis. The suprapatellar recess is compressed with one hand and try to push the patella into the knee with the other hand. In case intraarticular fluid is present, pushing the patella feels like it’s floating on fluid and you can “dip” it into the fluid.

MRI is the best modality to diagnose soft tissue injuries like ligament and meniscal injuries. Ultrasound may also be used. Radiography cannot diagnose ligament injury. MRI is not needed for diagnosis of MCL and LCL injury.

Treatment

ACL may be treated conservatively or surgically. Conservative therapy is indicated for chronic injuries, patients with minimal activity, if there is no instability, and if there is no associated injury. It involves immobilisation, brace, and physiotherapy.

In most cases, surgery is performed, as it allows return to activity sooner. Surgery is usually arthroscopic and involves reconstruction of the ACL with a tendon graft. Native (autograft), cadaver (allograft), or synthetic grafts may be used. Non-synthetic grafts are usually taken from patellar, hamstring, or quadriceps tendons.

Treatment of the unhappy triad requires surgical treatment with meniscal repair and ACL reconstruction. Management of PCL and LCL injury is similar as for ACL. Isolated MCL injury is managed conservatively, but multi-ligament injury is an indication for surgery.