Multi-Ligament Knee Injury

The four main knee ligaments

An isolated ACL tear is common. Injury to two or more of these, especially both cruciates, implies the joint was dislocated. See knee dislocation.

A knee dislocation (shinbone and thighbone separated) is different from a kneecap dislocation, which is much more common and less dangerous.

Why it is an emergency

Artery injury

The popliteal artery, the main blood supply to the lower leg, is tethered behind the knee and can be stretched, torn or blocked when the knee dislocates. Popliteal artery injury occurs in a significant proportion of knee dislocations. Without prompt repair, it can lead to loss of the leg. Damage may not be obvious at first, so blood flow is checked repeatedly.

Nerve injury

The common peroneal nerve wraps around the outer knee. Stretching injures it in a significant share of cases, particularly with outer-side ligament tears, causing foot drop (inability to lift the foot) and numbness on the top of the foot. Some recover over months; others do not.

Compartment syndrome

Swelling within the tight muscle compartments of the calf can cut off blood flow. Compartment syndrome causes severe pain out of proportion to the injury and needs emergency surgery.

Symptoms

• severe knee pain and rapid swelling
• obvious deformity if still dislocated (many reduce spontaneously before arrival)
• a knee that feels very unstable or wobbly
• inability to bear weight
• numbness, tingling or weakness in the foot
• a cool, pale foot with weak pulses

Diagnosis

• urgent examination: knee alignment, stability tests, pulses, foot color and temperature, and nerve function
• ankle-brachial index (ABI): comparing blood pressure at the ankle and arm; a low ABI prompts imaging of the artery
• CT angiography to assess the popliteal artery when needed
• X-rays: confirm the dislocation and check for fractures
• MRI after the emergency phase: shows which ligaments, menisci and cartilage are damaged

Treatment

Emergency phase

• reduction: putting the knee back in place, usually under sedation
• splinting or an external fixator to hold it stable
• vascular surgery to repair or bypass a damaged artery, sometimes with fasciotomy (releasing the calf compartments)
• serial checks of blood flow and nerve function for at least 24 to 48 hours

Ligament surgery

Most multi-ligament injuries need surgical reconstruction for a stable, functional knee. Surgery is often done within a few weeks of injury, once swelling settles. Depending on the injury, surgeons:

• reconstruct the cruciate ligaments with grafts
• repair or reconstruct the collateral ligaments and posterolateral corner
• repair menisci and treat cartilage damage

Some surgeons stage procedures. Some MCL injuries heal with bracing alone.

Rehabilitation

Rehab is long and demanding:

• protected motion and bracing for several weeks
• gradual strengthening and range-of-motion work
• return to daily activities within months; return to sport, if possible, usually takes 9 to 12 months or longer

Outlook

Many people regain a stable, functional knee for daily life after surgery and rehab, but some stiffness, reduced range of motion and activity limits are common. Return to high-level sport is possible for some. Long-term risks include knee arthritis. Outcomes are worse with artery or nerve injury.

Frequently asked questions

What is a multi-ligament knee injury?

It is a tear of two or more of the main knee ligaments (ACL, PCL, MCL and the lateral ligaments), usually caused by the knee dislocating. It is a serious injury that often needs surgery.

Why is a knee dislocation an emergency?

The main artery and an important nerve to the lower leg run behind the knee. A dislocation can damage the artery, threatening the leg, or injure the nerve, causing foot drop. Blood flow must be checked urgently even if the knee has gone back into place.

How long does recovery take after a multi-ligament knee injury?

Recovery is long. Daily activities are usually possible within a few months after surgery, but return to sports often takes 9 to 12 months or more, and some people have lasting stiffness or limits.

Can a multi-ligament knee injury heal without surgery?

Rarely. Some isolated collateral ligament tears heal with a brace, but tears of both cruciate ligaments or the posterolateral corner usually need surgical reconstruction for a stable knee.