The Rotator cuff refers to a group of muscles and tendons located in the shoulder which connect the arm with the upper torso. This part of the anatomy is critical to throwing a baseball.
One the most common - and devastating - type of injuries suffered by pitchers is a torn rotator cuff. While tendon injuries in the elbow are more frequent, they can often be repaired through surgery, with a good rate of success (see Tommy John surgery). In contrast, rotator cuff surgery, first attempted in the mid-1970s, has a very poor track record. While the surgery does address the pain and the daily-life issues created by a torn tendon or muscle, it also creates a stiffness that means that a pitcher cannot regain the freedom of movement he previously had in the shoulder, resulting in a significant loss of velocity. Don Gullett, Wayne Garland and Andy Messersmith, who were beneficiaries of long-term free agent contracts in the late 1970s, all underwent the surgery but were unable to regain effectiveness afterwards. As a result, the surgery has been abandoned in favor of rest and rehabilitation, and a closer monitoring of pitchers' workloads, through the use of pitch counts, for example.
Other injuries affecting the rotator cuff include tendinitis and bursitis. These can usually be treated with rest and physical therapy.