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)

Examination of an injured knee

  • The knee can be difficult to examine in the aftermath of an injury as pain and apprehension may limit examination findings and it is often helpful to see these patients again in 2-7 days to re-examine
  • If the injury is thought to be significant, with a suspicious history and possible multiple ligament injuries, an early MRI will help delineate the extent of injury

Classification of knee ligament injuries

  • Grade 1 (sprain): some fibres torn but macrosopic structure intact
  • Grade 2 (partial tear): some fasicles disrupted
  • Grade 3: complete tear

Overview of knee ligament biomechanics

  • MCL rupture may lead to valgus instability
  • ACL rupture may lead to rotatory instability
  • PCL rupture may lead to recurrent hyperextension or instability descending stairs
  • Posterolateral corner rupture leads to varus and rotatory instability
  • Multiligament injuries can result in gross instability

MCL injury

Mechanism of injury

  • Valgus stress with possible external rotation (e.g. rugby tackling from the side)

Clinical presentation

  • Knee swelling with ecchymosis, pain, deformity and instability
  • Medial joint line tenderness (over origin/insertion of MCL)
  • Medial joint laxity and pain on valgus stress

Investigations

  • Isolated MCL tear is a clinical diagnosis but x-rays and MRI can be used to rule out associated injuries

Management

  • Usually heals well, even if complete tear
  • Pain can take a few to several months to settle
  • Acute tears are usually treated in a hinged knee brace
  • Chronic MCL instability can be treated with MCL tightening (advancement) or reconstruction with tendon graft (rare)

ACL injury

  • Most commonly injured knee ligament

Mechanism of injury

  • Usually twisting sports injury
    • Higher rotational force, turning the upper body laterally on a planted foot - football, rugby, skiing
    • ACL is main stabilizer of internal of tibia
  • Higher incidence in females

Clinical presentation

  • Audible pop followed by deep knee pain and swelling (haemarthrosis) within an hour of the injury
  • Pain settles but leaves rotatory instability (gives way on turning on a planted foot due to excessive internal rotation of the tibia)
  • Excessive anterior translation of the tibia on the anterior drawer test and Lachman test

Investigations

  • Joint aspiration - haemarthrosis
  • MRI to confirm

Management

  • May cause little or no problems in some, whilst in others they can give substantial problems with function
  • Can stabilize with time and physiotherapy
  • Most have radiographic evidence of arthritis within 10 years (even those who have surgery)
ACL reconstruction (tendon graft)
  • Mainly indicated in rotatory instability not responding to physio
  • Other indications include as part of multiligament reconstruction or in professional athletes
  • Intensive rehabilitation is required and it may take up to a year to get back to high impact sports

LCL injury

  • Relatively uncommon
  • Often occurs in combination with PCL or ACL injury

Mechanism of injury

  • Usually occur with varus stress and hyperextension

Clinical presentation

  • Knee swelling with ecchymosis, pain, deformity and instability
  • Lateral joint line tenderness
  • Varus stress test - lateral joint laxity

Investigations

  • Isolated LCL tear is a clinical diagnosis but x-rays and MRI can be used to rule out associated injuries

Management

  • Complete rupture needs urgent repair if early (within 2-3 weeks)
  • Later diagnosis - reconstruction with tendon graft
  • Tends not to heal and can cause varus and rotatory instability
  • High incidence of common fibular nerve palsy
  • High incidence early OA of the knee

PCL injury

Mechanism of injury

  • Tend to occur following a direct blow to anterior tibia (e.g. dashboard, motorbike)
  • Isolated PCL rupture rare (usually occurs with other injury)

Clinical presentation

  • Popliteal knee pain and bruising
  • Positive posterior drawer test
  • Positive sag sign

Investigations

  • X-ray
  • MRI

Management

  • Most isolated cases don't require reconstruction
  • If patient develops instability (recurrent hyperextension or feeling unstable when going down stains) consider reconstruction
  • If part of multiligament knee injury usually requires reconstruction

Combined knee ligament ruptures

  • With higher degrees of force, some injuries can involve rupture of more than one of the four knee ligaments
  • Multi‐ligament knee injuries often require surgical reconstruction due to the degree of instability