Knee ligament injuries

Knee ligament injuries are often the result of rotational movement of the knee joint (e.g., cutting and pivoting movements in sports). Injuries to the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) result in knee pain and instability. Various maneuvers aid in demonstrating knee instability and are usually sufficient for the diagnosis of collateral ligament tears. An MRI is the best confirmatory test for cruciate ligament tears. Isolated ligament injuries are usually treated conservatively, but surgery is recommended for complex injuries, severe knee instability, and patients with physically demanding occupations.

• ACL and PCL connect the femur to the tibia.
• The MCL merges with the joint capsule of the knee.
• The LCL connects the femur and the fibula; It does not merge with the joint capsule of the knee.

Epidemiology

• Most commonly injured knee ligament ^[1][2]
• Higher incidence in female individuals

Mechanism of injury

• Low-energy noncontact: sports injuries with a twisting mechanism, e.g., football, soccer, basketball, baseball, alpine skiing, and gymnastics ^[3]
• High-velocity contact injuries (less common): direct blows to the knee causing forced hyperextension or valgus deformity of the knee

Clinical features

• History: Patients often report a popping sound shortly before the onset of symptoms.
• Physical examination findings
  • Knee swelling (e.g., due to hemarthrosis), pain, and instability
  • Positive Lachman test (most sensitive test)
    • With the knee joint at 20–30° flexion, the examiner stabilizes the femur and pulls the tibia anteriorly.
    • Increased tibial anterior gliding (compared to the opposite knee) and a soft endpoint indicate an ACL tear.
  • Positive anterior drawer test
    • With the knee joint at 90° flexion, the examiner fixes the foot on the table and pulls the proximal tibia forward.
    • Increased tibial anterior gliding (compared to the opposite knee) and a soft endpoint indicate an ACL tear.
  • Positive pivot shift test
    • With full extension of the knee joint, the examiner slowly flexes the knee while applying valgus stress with one hand and internally rotating the tibia with the other.
    • If the ACL is torn, the tibial plateau jerks backward at 30° of knee flexion.
• Commonly associated injuries
  • Most commonly lateral meniscus damage (often together with acute ACL and MCL injury)
  • Unhappy triad: simultaneous injury of the ACL, MCL, and medial meniscus (the medial meniscus is attached to the MCL)
    • Usually caused by valgus stress (lateral force) applied to the knee while the foot is fixed (e.g., during contact sports)
    • Clinical features: pain, instability, tender medial joint line, poor knee extension

Diagnostics

• Joint aspiration (in severe joint effusions): hemarthrosis
• MRI (confirmatory test)

Treatment

• Conservative treatment: for mild knee instability, less physically demanding occupations, premorbid inactivity, or postoperatively
  • RICE protocol
  • Analgesia
  • Physical therapy
• Arthroscopic surgery: for multiligament injuries, chronic knee instability, and for highly competitive athletes
  • Allograft from Achilles tendon or patellar tendon
  • Postoperative care: knee brace, crutches, physical therapy ^[4]
  • Double-bundle ACL graft using the semitendinosus and/or gracilis tendons (hamstring muscles)
  • ACL graft from the patellar tendon

Complications

• Meniscal degeneration
• Osteoarthritis
• Patella fracture
• Patella tendon rupture
• Reflex sympathetic dystrophy
• Postoperatively: graft failure, graft impingement

• Mechanism of injury
  • Noncontact injury involving hyperflexion of the knee with a plantarflexed foot (seen in athletes)
  • Direct posterior blow to a flexed knee, seen in motor vehicle accidents (dashboard injury) or athletic contact injury
• Clinical features
  • Initially vague symptoms: minimal (or absent) posterior knee pain, swelling, decreased functional range of motion
  • Positive posterior drawer test
    • With the patient lying supine and the knee at 90° flexion, the examiner fixes the foot on the table and pushes the proximal tibia backward.
    • Increased tibial posterior gliding (compared to the opposite knee) and a soft endpoint indicate PCL injury.
  • Positive posterior sag sign
    • The patient lies down with both hips and knees flexed and aligned together.
    • In this position, the tibia on the side of the torn PCL will appear to fall backwards under the influence of gravity.
  • Positive quadriceps active test
    • The patient is placed in supine position with the knee flexed at 90° with the foot flat on the bed.
    • The patient is asked to contract the quadriceps which, if there is PCL injury, should move the tibia forward.
    • If the tibia moves forward by more than 2 mm, then the test is positive.
  • Positive posterolateral drawer test
    • The patient is sitting on the edge of the examining table (thighs supported) with the legs hanging over the floor.
    • A posterior drawer test is performed which moves the lateral tibial plateau posteriorly around the axis of the PCL.
• Diagnostics
  • X-rays initially; : bony avulsions and posterior sag of the tibia
  • MRI (confirmatory test)
• Treatment
  • Conservative therapy for isolated injuries
  • Surgery for multiligament injuries, chronic knee instability, and for highly competitive athletes

MCL injuries are more common than LCL injuries.