Because of its location, from a direct blow to the front of the shoulder. A less frequent injury is a dislocation of the biceps tendon from its groove. This is usually seen in combination with a tear of the subscapularis tendon or the rotator cuff tendon which normally help hold the biceps tendon in it groove. The biceps tendon can also be injured at its attachment site on top of the glenoid. This usually involves an avulsion, where the tendon is pulled off the bone and rendered unstable.
Mild injuries can also result in microscopic tearing of individual tendon fibers.
As the severity of an injury increases, larger tears can occur to the point where the tendon is partially torn or even completely ruptured. If a rupture occurs, the long head will usually fall distally toward the elbow. Biceps muscle function usually remains nearly normal because of its dual attachment proximally. Initially, rest, ice, and gentle anti-inflammatory medications are all that is usually needed. Sometimes an injection with a strong anti-inflammatory medication such as cortisone is needed to control the pain and swelling.