The infraspinatus is one of the four muscles that make up the rotator cuff, a group of muscles and tendons that work together to support the shoulder. The muscle, which is roughly triangular in shape and is the largest of the four, lies behind the shoulder and works in conjunction with the others to stabilize it. It originates at and covers the scapula, or shoulder blade, and attaches to the humerus, or upper arm bone. The main function of the infraspinatus is to enable outward rotation of the arm.
An injury to the infraspinatus can occur due to overuse or repetitive motion of the muscle; along with the supraspinatus, it is the most frequently injured rotator cuff muscle. Sports that involve heavy use of the muscle, especially those such as baseball, tennis, or swimming where the arm is rotated often, may cause damage. Activities such as driving or using a computer that are done repeatedly and the arm is not supported may also be to blame. The muscle or its tendons may tear or they may become inflamed. Some people may suffer from impingement syndrome, where the tendon of the muscle is squeezed as it passes through a bony space in the shoulder called the subacromial space.
When the infraspinatus is injured, it will typically cause pain, stiffness, and weakness in the shoulder and upper arm, or even up into the neck. Movement of the arm, particularly reaching back or out to the side, may become difficult or impossible if the damage is severe enough. The pain may worsen at night and make sleeping difficult, particularly if laying on the injured side.
There are many ways to treat a damaged infraspinatus muscle. Ice can be applied to help reduce swelling, and medication can control the pain. The muscle should be rested to promote healing; this may mean immobilizing the arm with a sling to stop movement. Physical therapy with exercises to stretch and strengthen the area are often necessary. In cases of severe tears, surgery may be required.
To keep the infraspinatus from being injured, it is important to exercise and strengthen all of the rotator cuff muscles since they work together as a group. Lightweight training using rotational movements is a good way to target them. Stretching the muscles can also help prevent damage from occurring.