The orthopedic surgeon I saw at the clinic last week says I have a type I SLAP tear. It's in my left shoulder. Thankfully, I am right-handed. But I can't figure out how I got this because I haven't fallen down or done anything to hurt myself (that I remember, of course). How do these things develop?

SLAP stands for superior labral anterior-posterior. It refers to an injury affecting the labrum, a fibrous rim of cartilage around the edge of the shoulder joint. To help you better understand this, it might be helpful to review some basic anatomy. The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone), and the clavicle (collarbone). A part of the scapula, called the glenoid forms the shoulder socket. The glenoid is very shallow and flat. The labral rim of soft tissue makes the socket more like a cup. The labrum turns the flat surface of the glenoid into a deeper socket that molds to fit the head of the humerus.

The soft labral tissue can be caught between the glenoid and the humerus. When this happens, the labrum may start to tear. If the tear gets worse, it may become a flap of tissue that can move in and out of the joint, getting caught between the head of the humerus and the glenoid. The flap can cause pain and catching when you move your shoulder. Several tendons and ligaments attach to the labrum that help maintain the stability of the shoulder. So when the labrum tears, the shoulder often becomes much less stable.

Labral tears are often caused by a direct injury to the shoulder, such as a blow to the arm or falling on an outstretched hand. The labrum can also become torn from the wear and tear of activity, a condition called overuse. Repetitive overhead activities seem to be the greatest risk factor. Other risk factors include the way you are put together, in other words, the structure and shape of your anatomy and the way the bones meet together. The amount of natural shoulder rotation that is present as well as any retroversion (twist) of the humerus can make a difference. Tightness or contractures of the ligaments or capsule can alter the way the shoulder moves, setting off a cascade of biomechanical events that leads to a SLAP injury.