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Acute knee injuries

Consultant orthopaedic surgeon Mr Sean Curry advises on management, examination and when to refer acute knee injuries

Patients often limp in to Monday or Tuesday clinics following a knee injury they've sustained at the weekend. In some cases, you can afford to sit tight – but some will need referral for a specialist opinion.


It is sometimes not possible for the patient to remember exactly what happened, especially if the injury occurred in the excitement of a game, and some statements can be misleading.

If there is history of a twisting injury with a pop or a crack felt, then you should consider an anterior cruciate ligament (ACL) injury. You should also consider this if there was instant knee swelling. Not all patients will need surgery – but it's often worth them having an MRI and getting a specialist opinion, and at the very least some physiotherapy. Most acute ACL injuries are very painful and often the patient is unable to weight-bear.

Any case in which the knee is swollen and the patient cannot weight-bear will need an X-ray to exclude fracture. Your local A&E can supply the necessary crutches, but if the patient can get an early appointment at a fracture clinic or an acute knee clinic, even better.

Sometimes a meniscal tear can also lead to an inability to weight-bear, and again, early referral is advised, particularly if the displaced meniscal fragment is blocking full extension of the knee, leading to a locked knee.

Further down the line, ACL injuries lead to instability. Patients describe milder episodes similar to the original injury or sometimes just slight instability, felt as insecurity or a ‘wobble' of the knee. Ongoing meniscal problems are reported as a catching or clicking from the knee, sometimes with localised pain and intermittent swelling. A loose body in the knee gives very similar symptoms, but the site of the pain and catching moves around the knee.


Often, the injured knee is too swollen and painful for a meaningful examination. But if you do get the opportunity, you should ‘look, feel and move':

Look for swelling

If you can see a swollen knee, there is already a considerable effusion. If you need to look harder then there is either no swelling or only a mild to moderate effusion. Specialised tests include the patella tap and the bulge sign.

Feel for tenderness

Is there any local tenderness? Which side is it on? Is it on the joint line? Joint-line tenderness is one of the signs of a meniscal injury.

Move the knee

You should look for both the range of movement and also any excessive laxity caused by torn ligaments. Pain on stressing a ligament often indicates a partial injury or sprain, particularly if there isn't any excessive laxity. It is important to test the ACL as well as the collaterals. Special ACL tests are the Lachman test and the anterior drawer test.

The anterior drawer test is easiest to do and is performed with the knee flexed to 90 degrees. With the patient relaxed, apply a gentle anterior force to the tibia, attempting to pull it forward beneath the femur. Excessive movement indicates some degree of injury to the ACL. It is worth noting that a chronic posterior cruciate ligament (PCL) injury leads to a sag sign where the tibia falls backwards under the femur. This causes an apparent increase in movement on performing the anterior drawer test, because the starting point is more posterior, and so gives a false positive result.

The Lachman test is similar, but is done with the knee only flexed to about 30 degrees. It is harder to perform than the anterior drawer, but the test is more sensitive. The collaterals are tested with the knee slightly flexed to relax the joint capsule. You should apply a sideways force to the lower leg, looking for excessive play at the knee. It is always worth comparing movements with the opposite uninjured knee.

If the knee is not too painful or swollen, a McMurray test can also be performed. The knee is flexed up to 90 degrees and then straightened while applying a valgus or varus stress and internally or externally rotating the heel. A painful click indicates a possible meniscal tear.

Once you have done these tests you may well have a working diagnosis. You will then need to decide whether to refer urgently, refer non-urgently or adopt a waiting brief.


I suggest the following as a guideline:

• Always refer urgently: the very swollen knee, the patient who cannot weight-bear and the patient who cannot fully straighten their knee.

• Refer early: the suspected ACL or PCL tear, all ligament injuries with detectable laxity and all combination injuries (one or more of above).

• Routine referral: suspected meniscal tears and suspected loose body in the knee.

• Sit tight and refer if symptoms don't settle after six to eight weeks: the non-specific knee injury with mild swelling and the ligament sprain.

If we suspect a significant ligament injury or meniscal tear then we will refer the patient for a knee MRI. Sometimes this is available in primary care and so you might want to refer for this yourself.

Remember, after an acute injury, if it is going to get better on its own, it usually does so within six to eight weeks. If symptoms persist beyond this, consider referral. When in doubt, get in touch.

Mr Sean Curry is a consultant orthopaedic surgeon at The London Orthopaedic Clinic

The London Orthopaedic Clinic holds free monthly education sessions aimed at GPs, physiotherapists and allied health professionals. For more information about The London Orthopaedic Clinic, visit or call 0207 186 1000. Details of the education programme and the clinic's after-hours emergency service can also be found on the website.

Arthroscopic view of a torn anterior cruciate ligament A torn anterior cruciate ligament Cardinal signs, symptoms and treatment Cardinal signs, symptoms and treatment

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