Dislocation of the Knee

First aid for a suspected knee dislocation

1. Call 911 or your local emergency number.
2. Do not try to push the knee back into place yourself.
3. Keep the leg still in the position you found it, supported with rolled clothing or pillows.
4. Check the foot: is it warm, pink, and can the person feel touch and wiggle the toes? Tell the paramedics what you find.
5. Apply ice wrapped in a cloth around, not on, the deformity, and give nothing to eat or drink in case surgery is needed.

Knee dislocation vs kneecap dislocation

People often use "dislocated knee" for both. They are very different injuries.

For the far more common injury, see patellar dislocation.

Causes

• High-energy trauma: car and motorcycle crashes (the knee hits the dashboard), falls from a height, and pedestrian injuries.
• Sports: tackles in football and rugby, skiing and gymnastics.
• Ultra-low-velocity injuries: in people with severe obesity, stepping off a curb or a fall from standing can dislocate the knee. These injuries have a high rate of blood vessel damage.

Doctors classify dislocations by the direction the shinbone moves (anterior, posterior, medial, lateral or rotatory) and by which ligaments are torn. Anterior and posterior dislocations are the most common.

Symptoms

• Severe pain and a visibly deformed knee
• Rapid knee swelling, though swelling can be surprisingly mild if the joint capsule is torn and fluid leaks out
• Inability to stand or walk
• A knee that feels completely loose or "wobbly" in several directions
• Numbness, tingling or weakness in the foot, especially being unable to lift the foot up (foot drop)

About half of knee dislocations snap back into place before the person reaches the hospital. A straight-looking knee does not rule out a dislocation, so doctors treat any knee with three or more torn ligaments as a dislocation until proven otherwise.

Blood vessel and nerve injuries

The popliteal artery, the main artery to the lower leg, is tethered tightly behind the knee. When the bones shift, it can be stretched, torn or blocked by a clot. Without blood flow, muscle starts to die within about 6 to 8 hours. A missed popliteal artery injury is a leading cause of amputation after this injury.

The common peroneal nerve wraps around the outer knee and is injured in roughly a quarter of dislocations, especially those involving the outer ligaments. It causes numbness on the top of the foot and foot drop. About half of these nerve injuries recover at least partly.

Diagnosis

1. Rapid examination: foot pulses, skin color and temperature, sensation and movement.
2. Ankle-brachial index (ABI): blood pressure is compared at the ankle and the arm. A ratio under 0.9 suggests artery damage and needs imaging.
3. CT angiography: a dye scan of the leg arteries, used when the ABI is abnormal or pulses are reduced.
4. X-rays: confirm the dislocation and any fractures, before and after reduction.
5. MRI: maps which ligaments, cartilage and tendons are torn, once the person is stable.

Doctors also watch closely for compartment syndrome, a dangerous build-up of pressure in the calf muscles, for 24 to 48 hours.

Treatment

Emergency care

• Reduction: the bones are pulled back into place under sedation or anesthesia, as soon as possible.
• Splint or brace: the knee is held slightly bent, or in an external fixator (a frame with pins outside the skin) for very unstable or open injuries.
• Vascular surgery: a damaged artery is repaired or bypassed with a vein graft. If blood flow has been cut off for hours, surgeons may also open the calf compartments (fasciotomy).

Ligament reconstruction

Nearly all knee dislocations need surgery to restore stability. The surgeon repairs or reconstructs the anterior cruciate ligament, the posterior cruciate ligament and the collateral ligaments, often using grafts. Surgery may be done in one stage or two, usually within the first few weeks once swelling settles and blood flow is secure.

Older or less active people, or those with major other injuries, are sometimes treated with a long period in a brace instead, but this usually leaves more instability and stiffness.

Recovery time and outlook

• Weeks 0 to 6: brace, crutches and gentle range-of-motion exercises.
• Months 2 to 6: gradually bearing weight, strengthening and balance work.
• Months 9 to 12 or longer: return to running, sport or heavy work, if at all.

Most people regain a stable knee that works well for daily life. Stiffness, some loss of full bending, and long-term arthritis are common. Many athletes return to sport, though often not at their previous level. Outcomes are worse after artery injury, nerve injury or delayed treatment.

Frequently asked questions

Is a dislocated knee the same as a dislocated kneecap?

No. A dislocated kneecap means only the kneecap slides out of its groove. It is common and usually heals with a brace and physiotherapy. A true knee dislocation means the shin and thighbones separate, tearing several ligaments and often injuring the artery. It is a much more serious injury.

How long does it take to recover from a knee dislocation?

Expect about 9 to 12 months before returning to sport or heavy physical work, and up to 18 months for full recovery. Walking without crutches usually returns within about 2 to 3 months after ligament surgery. Recovery is longer if an artery or nerve was injured.

Can a dislocated knee go back in by itself?

Yes. About half of knee dislocations reduce on their own before reaching the hospital. The knee may look nearly normal, but the ligament and artery damage remains. Any severe knee injury with major instability needs an emergency check of blood flow to the foot.

Will I be able to walk normally after a knee dislocation?

Most people walk normally again after surgery and rehab, though the knee may stay slightly stiff or weaker. Foot drop from a nerve injury can cause a slapping gait and may need a lightweight ankle brace. Arthritis can develop over the following years.