ACL tear: the signs, the tests, and when surgery is needed
A pop in the knee, quick swelling and a knee that gives way. Here is what an ACL tear is, how it is diagnosed, and how doctors decide between physiotherapy and surgery.
OrthopaedicsRudraksh Healthcare team6 min read
The anterior cruciate ligament (ACL) is one of the four main ligaments that hold the knee together. It runs through the middle of the joint and stops the shin bone from sliding forward and twisting under the thigh bone. When it tears, the knee loses much of its stability.
How ACL tears happen
Most ACL tears happen without any contact: the foot is planted and the body twists, or a person lands awkwardly from a jump or changes direction suddenly. Football, cricket, kabaddi and basketball are common causes, but a fall on stairs or a slip on a wet floor can do it too.
Signs to look out for
- A pop or snap felt or heard in the knee at the moment of injury
- Swelling that builds up within a few hours
- Difficulty putting weight on the leg straight afterwards
- A feeling that the knee gives way or slips when turning, weeks later
The pain often settles within a couple of weeks, which leads many people to think the injury has healed. The instability usually remains, and repeated giving-way episodes can damage the meniscus and the cartilage of the knee.
How it is diagnosed
An orthopaedic doctor can often suspect an ACL tear from simple examination tests that check how far the shin bone moves forward. An X-ray rules out a fracture, and an MRI confirms the tear and shows any damage to the meniscus or cartilage.
Does every ACL tear need surgery?
Not always. The decision depends on your age, how active you are, whether the knee keeps giving way, and whether other structures are injured.
- Physiotherapy alone may be enough for less active people whose knee feels stable in daily life.
- Reconstruction surgery is usually advised for young and active people, those who play sport, and anyone whose knee keeps giving way.
ACL reconstruction is done arthroscopically, through small cuts. The torn ligament is replaced with a graft, usually taken from the patient's own hamstring tendons. Most patients walk with support within days, and rehabilitation continues for several months before a return to sport.
What to do right after a knee injury
- Stop playing; do not try to walk it off
- Rest, apply ice wrapped in a cloth, and keep the leg raised
- Use a crepe bandage for gentle support
- See an orthopaedic doctor within a few days, sooner if the knee is locked or you cannot bear weight
This article is general health information, not medical advice. Everyone is different: please consult a doctor about your own symptoms and treatment.