An avulsion occurs when the tendon of a muscle tears off the bone where it attaches. Two of the most typical muscles that this occurs with are the biceps and the gastroc. It has been known to happen with the hamstrings as well. Sometimes a part of the bone comes off with the muscle.

The gastroc muscle is the large muscle on the back of the calf. It runs from the knee area and attaches to the heel bone (called the calcaneous). This attachment at the heel bone is usually where the avulsion occurs. It can happen in many ways. A quick, vigorous stretch to the muscle, such as stepping back while playing tennis or similar sporting activity, can be one method. Sometimes a fall onto the foot can create this avulsion. Or, it may be associated with a motor-vehicle accident.

The biceps muscle is located in the front part of the upper arm. It runs from the shoulder and attaches in the front of the forearm just below the elbow. Again, a quick, vigorous stretch can cause an avulsion, usually at the attachment at the forearm. This can occur in an activity such as gymnastics or martial arts when the arm is stretched into a straightened position from a bent position.

The initial symptom is pain at the point where the avulsion occurs. Bruising in that area is also quite common. Weakness in that joint or inability to move the joint is typical since the muscle is no longer there. However, in the biceps avulsion there is another muscle under the biceps that can help move the elbow. In the gastroc injury, while there are some small supporting muscles for the ankle, movement is usually not possible. One of the most visible signs is a bulge or a ball under the skin. With the biceps injury, this ball is located in the middle of the upper arm. With the gastroc injury, the ball is located in the middle of the calf. This ball is the contracted, bunched up muscle.

Treatment involves surgery to reattach the muscle to its original attachment. In the case of the biceps avulsion, surgery may not be needed since there is another major muscle in the arm (the brachialis) that can compensate. The decision to operate depends on age and activity level. A young professional gymnast may need the extra strength the biceps adds to the arm, whereas an elderly retired person may be able to regain moderate functional activity with just the remaining muscle. With the gastroc avulsion, surgery is always indicated because of the importance of the gastroc muscle in walking.

After surgery, immobilization by cast or splint is necessary to allow the repair to heal. This is usually required for at least 4-8 weeks depending on the procedure and extent of the injury. After removal of the cast or splint, rehabilitation begins with gentle passive and assisted range-of-motion exercises. Modalities may be used to control pain, reduce inflammation and promote continued healing. As therapy progresses, the therapeutic exercise program moves into general active range of motion and then into gradual strengthening. The final stages of rehabilitation concentrate on return to functional activity.

In the case of not surgically repairing the biceps, treatment begins with modalities, active and active assisted exercise, and generally progresses to strengthening the remaining muscle and engaging in functional exercise activity.