Knee dislocation

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Knee dislocation

What is knee dislocation?

A dislocated knee is a serious injury in which the thigh bone (femur) and the shin bone (tibia) become disconnected. This is different from a dislocated kneecap, which is when the kneecap (patella) becomes detached from its groove at the end of the femur. It should also not be confused with a partial dislocation (subluxation) which is due to a damaged ligament and can cause the knee to give way temporarily until the bones slip back into place.

A dislocated knee is a relatively uncommon injury but is potentially very serious and no attempt should be made to reposition the knee without professional medical support as this can result in:

Deep vein thrombosis
Damage to the peroneal nerve, which runs along the outer edge of the calf.
Rupture or obstruction to the popliteal artery and vein at the back of the knee.

It is essential to seek medical help immediately to prevent potentially devastating damage to the knee and lower leg. If you develop a vascular obstruction and it is not treated for eight hours or more there is an extremely high (86%) risk of amputation.

Knee dislocation is not the same as kneecap (patella) dislocation.

What causes a dislocated knee?

A dislocated knee is often the result of a high impact injury such as a road traffic accident, a sporting injury or a serious fall. It can also be caused by a relatively minor injury, such as a missed step or unusual twist.

What are the symptoms of a dislocated knee?

Among the symptoms of knee dislocation are:

Extreme pain that is worsened by attempting to move the knee.
Deformity of the knee joint.
Shortening and misalignment of the lower leg.
Obvious swelling.

How is a dislocated knee diagnosed?

A dislocated knee is a medical emergency and the joint will be repositioned as soon as you arrive in the emergency room. Once it is back in position, the surrounding tissues, nerves and blood vessels will need to be assessed for damage. It is highly likely that you will have tearing or rupturing of the anterior cruciate ligament and posterior cruciate ligament. You may also have damage to the cartilage, collateral ligaments and meniscus.

To diagnose the type and extent of these injuries you will be referred for an X-ray or CT scan which can show misaligned bones. An MRI scan may be used to assess the extent of damage to ligaments, tendons and cartilage. Your consultant may also order a CT angiogram, which is a special type of CT scan that uses an injection of dye into the vein to map blood flow. This can help to diagnose vascular obstruction. A Doppler ultrasound may also be used to assess arterial blood flow. Any nerve damage will be assessed using a physical examination to check for impaired foot movement or sensations of numbness or pain.

How is a dislocated knee treated?

Initially, the priority is to minimise damage to blood vessels and nerves. Once these have been stabilised, damage to surrounding tissues can be addressed. A dislocated knee may require multiple surgical procedures to repair the extensive damage that can occur. These may be performed as arthroscopic (keyhole) surgery, using a tube-like instrument called an arthroscope, or open surgery which uses larger incisions.
You may require surgery to repair ligament and cartilage damage and meniscus tears . If you have arterial injuries you may be offered surgical repair using a synthetic patch, graft or transplanted vein. Alternatively you may need an arterial bypass or an embolectomy to remove a clot. If cartilage has been lost, you may need cartilage implantation or cartilage transfer.

After a knee dislocation you will require extensive physiotherapy and rehabilitation to restore knee function. Without proper rehabilitation, there is a risk of chronic knee stiffness, instability and post-operative nerve pain.