Knee Contusion (Bruised Knee)

What happens in a knee contusion

A blow crushes small blood vessels. Blood leaks into the tissues, causing swelling and discoloration. Depending on the force:

• Superficial contusion: skin and fat bruising, with a visible bruise.
• Prepatellar bursa bleeding: the fluid sac in front of the kneecap fills with blood, causing a soft, squashy swelling over the kneecap. See prepatellar bursitis.
• Muscle contusion: usually the quadriceps just above the knee.
• Bone bruise: small fractures inside the bone (microtrabecular injury), seen only on MRI. They often accompany ligament tears.

Symptoms

• pain at the site of the blow
• swelling, which may spread around the knee
• bruising: red or purple, changing to blue, green and yellow over 1 to 2 weeks
• tenderness to touch
• stiffness and pain when bending or kneeling
• deep, aching pain with a bone bruise, sometimes lasting weeks

When to get an X-ray: the Ottawa knee rule

Doctors use the Ottawa knee rule to decide who needs an X-ray after a knee injury. An X-ray is recommended if any of these apply:

• age 55 or older
• tenderness at the head of the fibula (outer knee)
• tenderness isolated to the kneecap
• inability to bend the knee to 90 degrees
• inability to bear weight for 4 steps, both immediately and in the emergency department

Conditions to rule out

Treatment

First 48 to 72 hours

• Rest: avoid activities that cause pain. Use crutches if walking hurts.
• Ice: apply an ice pack wrapped in a cloth for 15 to 20 minutes every 2 to 3 hours.
• Compression: a snug elastic bandage, not so tight that it causes numbness or tingling.
• Elevation: keep the knee above heart level when possible.
• Pain relief: acetaminophen (paracetamol) or an NSAID such as ibuprofen. Follow the label dose.

After the first few days

• gentle range-of-motion exercises, such as heel slides and straight-leg raises, to prevent stiffness
• gradually return to walking, stairs and normal activities as pain allows
• quadriceps strengthening as swelling settles
• protective knee pads for sports or work that involves kneeling

Bone bruises

Bone bruises need more time. Protect the knee with reduced impact and, sometimes, crutches. Return to running and sport usually takes 6 to 12 weeks, guided by pain.

Healing time

Complications

• myositis ossificans: bone forming within a severely bruised muscle, usually the quadriceps, causing a firm lump and stiffness
• infection of a bursa or a wound
• persistent pain from an unrecognized ligament or cartilage injury

Frequently asked questions

How long does a bruised knee take to heal?

Most simple knee bruises heal within 1 to 3 weeks. Larger bruises with significant swelling can take up to 4 to 6 weeks. Bone bruises, seen on MRI, may take 1 to 3 months to stop aching.

How do I know if my knee is bruised or broken?

A fracture is more likely if you cannot bear weight for 4 steps, cannot bend your knee to 90 degrees, cannot straighten your leg, or the kneecap is very tender or misshapen. These signs mean you need an X-ray.

Should I walk on a bruised knee?

Yes, if you can walk comfortably. Gentle walking and movement prevent stiffness. Use crutches for a few days if walking is painful. Avoid running, jumping and kneeling until pain and swelling settle.

What is a bone bruise in the knee?

A bone bruise is bleeding and swelling within the bone after an impact, often seen on MRI alongside ligament injuries. It causes deep, aching pain and usually heals in 1 to 3 months with reduced impact activity.

Should I use heat or ice for a bruised knee?

Use ice for the first 48 to 72 hours to reduce swelling and pain. After that, gentle warmth may ease stiffness. Avoid heat in the first couple of days, because it can increase swelling.