avulsion injury

Avulsion injuries or fractures occur where the joint capsule, ligament, tendon or muscle attachment site is pulled off from the bone, usually taking a fragment of cortical bone. Avulsion fractures are commonly distracted due to the high tensile forces involved. There are numerous sites at which these occur. Being familiar with them is important as subacute/chronic injuries can appear aggressive.

Epidemiology

Avulsion injuries are common among those who participate in sports, in particular adolescents.

Pathology

Avulsion fractures can be classified as acute, subacute or chronic. In acute avulsion fractures, there is usually a clear preceding traumatic incident. Subacute and chronic avulsion injuries can be due to delayed presentation of an acute injury or secondary to repetitive use / overuse injuries .

The mechanism is from either :

  • high muscle activity
  • forced extreme range of motion
Location
Shoulder girdle
  • greater tuberosity: insertion of rotator cuff
  • lesser tuberosity: insertion of subscapularis (rare)
  • coracoclavicular avulsion
Elbow
Hand
Pelvis and hip
Knee
Ankle and foot

Radiographic features

Many avulsion fractures are apparent of plain radiographs. The avulsed bone fragment is typically displaced in the direction of the tendon, ligament or joint capsule which is attached to it . CT and/or MRI may be required for detection and further characterization. Appearances will vary depending on classification :

  • acute: avulsed bone fragment with donor site and typically associated soft tissue swelling / joint effusion
  • subacute: fracture healing results in a mixed lytic/sclerotic appearance
  • chronic: sclerosis and osseous hypertrophy

On MR small avulsion fractures can easily be missed, as the avulsed cortical fragment is often poorly visualized, and the bone marrow edema is absent at the site of injury .

Treatment and prognosis

Most avulsion injuries/fractures are treated non-operatively .

Differential diagnosis