Avulsion Fracture

What causes an avulsion fracture

Tendons attach muscles to bone, and ligaments attach bone to bone. When a muscle contracts very forcefully, or a joint is twisted suddenly, the tendon or ligament can be stronger than its attachment point, so it pulls off a fragment of bone rather than tearing itself.

Teenagers are particularly prone, because the growth plates and apophyses (bony bumps where tendons attach) are weaker than the tendons until the skeleton matures, usually by the late teens or early twenties. Older adults with weaker bones can also get avulsion fractures from relatively minor injuries.

Common avulsion fracture sites

Symptoms

• sudden, sharp pain at the moment of injury, sometimes with a pop. In the ankle this is felt as ankle pain on the outer side
• swelling and bruising over the bone
• pinpoint tenderness at the attachment point
• difficulty walking, bearing weight or using the joint
• weakness of the muscle that pulled the fragment, for example being unable to straighten a fingertip
• in hip and pelvic injuries, pain when contracting the muscle against resistance

Avulsion fracture vs sprain

Ankle avulsion fractures are often first thought to be sprains, because the injury and symptoms are similar. Clues pointing to a fracture include tenderness directly over the bone rather than the soft tissue, and being unable to take 4 steps. Doctors use the Ottawa ankle and foot rules, based on bony tenderness and ability to walk, to decide who needs an X-ray.

Diagnosis

• Examination: locating tenderness, checking joint stability, muscle strength and circulation
• X-ray: shows most avulsion fractures as a small fleck of bone separated from the main bone
• Ultrasound or MRI: for subtle fragments, tendon or ligament injury, and hip and pelvic injuries
• CT: for complex joint fractures and surgical planning

Treatment

Most avulsion fractures: non-surgical care

• Rest and protection: a walking boot, stiff-soled shoe, brace or splint depending on the site
• Ice for 15 to 20 minutes several times a day for the first 2 to 3 days
• Elevation to reduce swelling
• Pain relief: acetaminophen (paracetamol) or ibuprofen at the label dose
• Crutches for a short time if weight-bearing is painful
• Physical therapy: gradual range-of-motion, stretching and strengthening once pain settles, then a return-to-sport program

Mallet finger is treated with a splint holding the fingertip straight continuously for 6 to 8 weeks. Bending the tip even once during that time can restart healing.

Hip and pelvic avulsions in teenagers usually heal with crutches, rest and a staged rehabilitation program over 6 to 12 weeks.

Surgery

Surgery is considered when:

• the fragment is large or displaced by more than about 1 to 2 cm (varies by site)
• a joint surface is involved or the joint is unstable
• the tendon has lost its function, such as some hamstring avulsions in adults
• a fracture is not healing

Fragments are reattached with screws, pins or anchors.

Healing time

Return to sport usually requires full, pain-free movement and normal strength.

Complications

• slow healing or non-union, especially where blood supply is limited
• chronic instability or weakness
• stiffness of nearby joints
• a bony lump where healing occurs
• in growing children, rarely, effects on growth

Prevention

• warm up before sprinting and kicking
• build flexibility and strength gradually, especially in the hamstrings, hips and calves
• avoid sudden increases in training intensity, which also cause stress fractures
• wear supportive footwear and use ankle braces after previous sprains

Frequently asked questions

What is an avulsion fracture?

It is a fracture where a tendon or ligament pulls a small piece of bone away from where it is attached. It happens with sudden forceful muscle contractions or twisting injuries, commonly at the ankle, foot, hip and fingers.

How long does an avulsion fracture take to heal?

Most heal in 4 to 8 weeks. A fifth metatarsal avulsion usually takes 6 to 8 weeks, a mallet finger needs 6 to 8 weeks of continuous splinting, and hip or pelvic avulsions in teens often need 6 to 12 weeks before returning to sport.

Can you walk on an avulsion fracture of the ankle or foot?

Often yes, in a walking boot or stiff-soled shoe, as pain allows. Many fifth metatarsal and ankle avulsion fractures are treated this way. Your doctor will advise based on the X-ray, and crutches may be used for the first days.

Does an avulsion fracture need surgery?

Most do not. Surgery is reserved for large or widely separated fragments, injuries involving the joint surface, unstable joints, or fractures that fail to heal. Some adult hamstring avulsions are repaired surgically for best strength.

Is an avulsion fracture worse than a sprain?

It is a type of fracture, but it often behaves much like a severe sprain and heals with similar treatment. It may need longer protection than a mild sprain. Getting it diagnosed ensures the right protection and avoids long-term instability.