Anterior Cruciate Ligament rupture (ACL)
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Anterior cruciate ligament (ACL) ruptures are common sporting injuries. If untreated, they can result in chronic knee instability, and resultant degenerative changes – such as arthritis, and chondral damage.

Early diagnosis and treatment can prevent this long-term damage.

Treatment typically involves ligament reconstruction. Colloquially “knee reconstruction” surgery typically refers to ACL repair.

There is a high success rate of return to sport at all levels of competition after surgery.

Epidemiology and Aetiology

  • ACL rupture accounts for half of all knee injuries
  • Incidence of about 1 in 3000 per year
  • More common in females (4:1)
    • Thought to be due to altered landing biomechanics (quad dominance)
  • Particularly risky sports include basketball, skiing and football (soccer)
  • May be associated with meniscal tear and medial collateral ligament injury.
    • Triad of ACL, medial meniscus and medial collateral ligament is common


  • The anterior cruciate ligament is made up of two bundles of fibres, anteromedial and posterolateral bundles
  • Made up of 90% type I collagen and 10% type III collagen
  • Blood supply is via the middle geniculate artery
  • Innervated by the poster articular France of the tibial nerve
  • Function –¬†prevents¬†anterior translation of the tibia relative to the femur
Anatomy of the knee
Anatomy of the knee
Anatomy of the knee
Anatomy of the knee

Mechanisms of injury

  • Internal tibial rotation on a flexed knee (pivoting injury) – typically when landing from a jump, or quickly pivoting
  • Strong valgus force / force applied to lateral aspect of the knee – e.g. a rugby tackle or football tackle on a fixed foot


  • Acute onset of pain during sport
  • “Felt a pop”
  • Pain deep inside the knee
  • Acute onset swelling (70% of cases) – typically <30 minutes since injury
  • Difficulty weight bearing
  • Sensation of knee instability


On knee examination:

  • Large knee effusion
  • Positive drawer test (either direction, but classically anterior drawer test)
  • Lachman test – lacks and endpoint
    • Movement >5mm is abnormal
    • Compare with the other side
    • A Lachman test is a modified drawer test with he knee flexed only to 15-20 degrees



  • AP, lateral, skyline view
  • Often normal
  • A¬†Segond fracture –¬†avulsion of the proximal tibia –¬†is diagnostic for ACL injury


  • Can confirm ACL rupture


Conservative management

  • May be appropriate in some cases
  • Be aware of the increased risk of long-term meniscal and other injury
  • Suitable for sedentary patients, or those in recreational level sport without any pivoting activities
  • Typically involves a period of rest for 6-8 weeks followed by 3 months of graduated return to activity under supervision of physiotherapist

Operative management

  • ACL reconstruction
    • Younger, active patients
    • Can restore full ROM to the knee
    • Typically a graft is used
    • Autografts(from another site within the patient)¬†are typically from the patellar tendon (most common) hamstring or quadriceps tendon
    • Allografts¬†(from another patient)
    • There is not clear evidence as to which techniques is best – both have pros and cons. One major difference is the requirement to harvest the autograft, which can result in secondary issues – such as patellar tendon rupture (typically occurs during rehab phase), or long-term hamstring weakness. Allografts also have a higher risk of re-ruptre compare to autografts when used in younger patients, and there is a small chance of disease transmission (such as HIV) – but risk is extremely low (<1:1million)
    • Complications
      • Septic arthritis (<1%)
      • Failure of graft
      • Reduced ROM following procedure (can be minimised with effective rehab)
      • Patella tendon rupture (if used for graft)
  • ACL repair
    • High failure rates
    • Not widely practised

Concurrent meniscal and collateral ligament injuries should be treated at the same time and when treated, improve the overall outcome.

Post-op rehabilitation

  • Immediate
    • Ice
    • Immediate weight bearing (reducing long-term patellofemoral pain)
    • Early full passive extension
  • Early
    • Avoid exercises that stress the graft
    • Eccentric strengthening at 3 weeks
    • Core and gluteal strengthening
    • Squats and leg press are suitable exercsies
  • Return to play
    • Typically no sooner than 9 months post surgery (poor evidence for this recommendation)
      • Earlier return associated with higher re-rupture rates
    • Only return once has passed sport specific exercise tests – such as hopping on one leg
  • Prevention of re-rupture
    • Land from jumping with more knee flexion
    • Hamstring strengthening to reduce quad dominance
    • “Fall” training – especially for skiers!



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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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