Torn ACL: symptoms, treatment, and whether you need surgery

“Do I need surgery?” is the first question almost every patient asks after an ACL rupture, and it rarely has a one-word answer. The honest position is that some people with a torn ACL need reconstruction, some do not, and the difference between them has less to do with the scan than with what the knee is being asked to do.

What the ACL does

The anterior cruciate ligament stops the tibia sliding forward on the femur and controls rotation. Walking in a straight line does not test it much. Pivoting, cutting, decelerating and landing do. That is why two people with identical MRI findings can have completely different experiences. One is a netballer, the other rides a bike to work.

ACL tear symptoms: how the injury happens

A pivot, a landing, a sharp change of direction, and then a pop, a giving way, and a knee that is suddenly, completely unreliable. For athletes in particular, it is one of the most psychologically and physically disruptive injuries in sport.

The anterior cruciate ligament is not a large structure, roughly the size of a finger, but it is the primary restraint to forward movement of the shin bone on the thigh bone, and the key controller of rotational knee stability. When it ruptures, that stability disappears.

How it is diagnosed

MRI defines the meniscus, the articular cartilage and the other ligaments. A locked knee or a displaced meniscal tear moves the timeline forward. It is not a decision that should be made from an MRI report alone.

The factors that drive the decision

Does the knee give way?

This is the single most important piece of information, and it comes from the patient, not the scan. A knee that buckles during ordinary activity is an unstable knee, and repeated giving-way episodes damage the meniscus and articular cartilage. Instability that persists after a proper rehabilitation programme is a strong indication for reconstruction.

What sport or work do you want to return to?

Pivoting sports such as Australian football, netball, soccer, basketball and skiing place demands on the knee that an ACL-deficient joint frequently cannot meet. Occupations involving ladders, uneven ground or heavy manual work sit in the same category. Running, cycling, swimming and gym work generally do not.

Is there an associated injury?

A repairable meniscal tear, particularly a bucket-handle tear or a root tear, changes the calculus considerably. Those injuries are best addressed early, and if the knee is being operated on anyway, the ligament is usually reconstructed at the same time. A knee that is locked and cannot be straightened needs surgery regardless of the ligament.

Your age and the state of the joint

Younger patients tend to have higher activity demands and more years of loading ahead of them. An older patient with established arthritis in the same compartment may get little benefit from reconstruction and considerable benefit from targeted rehabilitation.

How does the knee respond to rehabilitation?

This is the factor most often skipped. A structured programme of quadriceps and hamstring strengthening, neuromuscular control and progressive loading resolves symptoms for a meaningful proportion of patients. Those who regain a stable, strong knee and stay stable when they return to their activities are described as ‘copers’. Identifying them takes a properly supervised trial of rehabilitation, not a guess.

Treatment without surgery: a reasonable sequence

1. Settle the acute knee. Swelling, pain and loss of movement all distort the examination. Regaining full extension and reducing swelling comes first.
2. Establish what else is injured. MRI defines the meniscus, the articular cartilage and the other ligaments. A locked knee or a displaced meniscal tear moves the timeline forward.
3. Rehabilitate properly. For a patient without a surgical meniscal problem, a supervised programme over several weeks tells you a great deal about how the knee will behave.
4. Reassess against the real goal. If the knee is stable through the activities the patient actually wants to do, reconstruction may not be needed. If it gives way, or the goal is a pivoting sport, reconstruction is the reliable option.

Delaying a decision is not the same as losing the option. A brace-based approach is covered in the Cross Bracing Protocol: can a torn ACL heal without surgery? For most patients, a period of rehabilitation before committing to surgery does not compromise the result of reconstruction later, and it often improves it. Patients who go into surgery with a strong, straight, quiet knee do better afterwards.

When surgery is recommended

When surgery is agreed upon, the timing matters. Operating on an acutely swollen, stiff knee, particularly within the first two to three weeks of injury, significantly increases the risk of post-operative stiffness and scarring of the joint (arthrofibrosis). Dr Mooney prefers to operate once the swelling has settled, full passive extension has returned, and the patient has achieved at least 120 degrees of flexion. This typically takes four to six weeks.

ACL reconstruction rebuilds the torn ligament using a tendon graft taken from elsewhere in the body. There are three main options, and the evidence does not decisively favour any single one over the others in terms of overall outcome. The choice is covered in ACL graft options, and the added stabilising procedure for selected patients in the LET procedure.

Approximately 85% of patients who undergo ACL reconstruction return to some level of sport. Around 65% return to their pre-injury level of competition.¹

What the decision is not

It is not a decision that should be made from an MRI report alone, and it is not a decision that should be made by anyone who has a financial interest in one answer. A surgeon who recommends reconstruction for every ACL tear and a therapist who recommends against it for every ACL tear are making the same error.

Seeing a knee specialist

Dr Mooney consults at Eastwood, Tea Tree Gully (North East Health Centre), Woodville, Naracoorte and Mount Gambier.

If you have torn your ACL and you are trying to work out what to do, the useful first step is an assessment that covers the whole knee, your activity goals and the rehabilitation options, before anyone talks about a date for theatre. If reconstruction is the right answer, it will still be the right answer in six weeks.

Common questions