Anterior Cruciate Ligament Injury

• Types of ligament injuries in the knee

  • Anterior Cruciate Ligament (ACL)
  • Posterior Cruciate Ligament (PCL)
• Damage to the ACL is common, particularly amongst athletes
• PCL injuries are less common
• Basic Anatomy of the knee

  At the top of the tibia, there are the medial and lateral condyles, which correspond to the condyles of the femur. Between the condyles, there is an intercondylar area. The ACL attaches at the anterior intercondylar area on the tibia. The PCL attaches at the posterior intercondylar area on the tibia. The femur has rounded areas called condyles and an intercondylar notch at the back of the distal end, which is a groove between the two condyles. Both cruciate ligaments originate from the intercondylar notch, the ACL on the lateral aspect and the PCL on the medial aspect. The ACL prevents the tibia from sliding forward in relation to the femur. The PCL stops the tibia from sliding backward in relation to the femur
• The ACL is typically damaged during a twisting injury to the knee
• Symptoms of ACL injury

  • Pain
  • Swelling
  • "Pop" sound or sensation
  • Instability of the knee joint
• Patients with ACL injuries

  Experience instability of the knee joint, with the tibia moving anteriorly below the femur, knee buckling, lack of confidence in knee stability, muscle weakness over time, and increased risk of other knee injuries like meniscal tears
• Anterior drawer test


  Used to assess for anterior cruciate ligament damage. The patient is supine with the hip flexed to 45 degrees and the knee flexed to 90 degrees, with the foot flat on the couch. The examiner sits on the patient’s toes to stabilise the foot
• Anterior drawer test


  Patient is supine with the hip flexed to 45 degrees and the knee flexed to 90 degrees, with the foot flat on the couch. The examiner sits on the patient’s toes to stabilise the foot. The examiner holds the leg just below the knee and pulls the proximal tibia anteriorly, sliding it forward from the femur at the knee. In a normal knee, there will be slightly anterior movement of the proximal tibia but a definite end-point to movement, as the ACL holds the joint securely. With ACL damage, the tibia can move an excessive distance anteriorly, and the examiner will not be able to feel a clear end-point to the movement
• Lachman test


  Similar to the anterior drawer test, but the knee is tested while flexed at around 20-30 degrees
• Examination can be difficult to interpret shortly after the injury due to pain and swelling
• Examination after the acute pain and swelling has settled is more likely to be accurate
• Investigations

  1. MRI scan is usually the first-line imaging investigation for establishing the diagnosis

  2. Arthroscopy can be used to visualise the cruciate ligament and is the gold-standard investigation for diagnosing a cruciate ligament tear
• Management

  The NICE clinical knowledge summaries on knee pain (updated 2017) recommend urgent referral in patients with an acute onset of knee pain associated with symptoms suggestive of an acute anterior cruciate ligament tear. Local pathways vary, and this may involve sending the patient to A&E or the fracture clinic. Symptoms suggestive of an acute anterior cruciate ligament tear include: A “pop”, Rapid onset swelling, Instability or giving way
• Conservative management

  1. Involves RICE: R – Rest, I – Ice, C – Compression, E – Elevation

  2. NSAIDs are usually used first-line for analgesia in MSK injuries

  3. Crutches and knee braces may be required to help protect the knee while mobilising

  4. Physiotherapy can be used before and after surgery for rehabilitation
• Arthroscopic surgery


  To reconstruct the ligament is often required, particularly in active and young patients. The type and timing of surgery will be based on individual factors, such as the extent of the ACL injury and the patient’s activities (e.g., are they a young competitive athlete or a sedentary older patient). A new ligament is formed using a graft of tendon from another location. Options for graft tendons used to reconstruct the ACL include: Hamstring tendon, Quadriceps tendon, Bone-patellar tendon-bone (taking part of the patella tendon as well as the bone it inserts into)
• Last updated

  August 2021