Anterior cruciate ligament injury
Also known as: ACL tear, torn cruciate, knee ligament injury
A sprain or tear of the anterior cruciate ligament, the band inside the knee that stops the tibia sliding forward on the femur and controls rotation.
Overview
ACL tears happen in a moment: a pivot, a sudden stop or a landing with the knee twisted inward, often with a pop and rapid swelling. The knee then gives way on turning. Young athletes, especially women, are most affected. Whether to reconstruct the ligament depends on the person's activity and instability.
Causes
- Non-contact pivoting, cutting or landing injuries (70%)
- Direct blows to the knee
Risk factors
- Football, skiing, basketball, netball
- Female sex
- Poor landing mechanics and hip weakness
- Previous ACL injury
- Fatigue
Symptoms
What a clinician may find
- A pop at injury, swelling within hours (haemarthrosis)
- Positive Lachman and anterior drawer tests
- Giving way on pivoting
Complications
- Meniscal and cartilage damage
- Recurrent instability
- Early osteoarthritis
Diagnosis
History and examination; MRI confirms the tear and shows associated meniscal, collateral ligament and bone injuries. X-rays exclude fracture.
Treatment
Immediate: rest, ice, compression, elevation and early physiotherapy. Structured rehabilitation restores function in many people; surgical reconstruction with a tendon graft (hamstring, patellar or quadriceps) is chosen for those with instability or pivoting sports, followed by 9 to 12 months of rehabilitation.
Prevention
Neuromuscular training programmes (landing technique, hip and hamstring strength, balance) cut injury rates by half in athletes.
When to seek care
Same-day assessment for a knee that swelled rapidly after a twisting injury, cannot straighten, locks or feels unstable.