There are two types of shoulder instability depending on the cause of occurrence: traumatic and non-traumatic. Understanding the difference between the two is the key to proper treatment. In general, an injury that causes recurrent and repeated dislocations of the shoulder is considered traumatic shoulder instability; non-traumatic shoulder instability is a loosening of the joint, which eventually leads to shoulder instability. Traumatic shoulder instability is most common in the young, athletic population. The younger and more active a patient is when they first experience a shoulder dislocation or shoulder dislocation, the more likely they are to develop recurrent shoulder instability, also known as habitual shoulder dislocation. For example, patients who have their first shoulder dislocation in their teens have a 20% chance of developing recurrent shoulder instability, and patients who have their first shoulder dislocation over the age of 40 are less than 10% likely to develop chronic shoulder instability. What is traumatic shoulder instability? Traumatic shoulder instability begins with the first shoulder dislocation, which damages the ligaments that support the shoulder joint. The surface of the articular glenoid (shoulder socket) is relatively flat and is deepened by the glenoid labrum, a cup of cartilage that can encircle part of the humeral head. The glenoid labrum acts as a bumper to hold the humeral head firmly in place in the glenoid, and it is also the attachment point for stabilizing the shoulder ligaments. When the glenoid labrum is torn from the glenoid, the support of these ligaments ceases to exist. The development of recurrent instability in the shoulder is inextricably linked to the type and extent of injury to the glenoid labrum and surrounding ligaments. The most common types of traumatic instability of the shoulder joint are forward and downward instability. Common causes of injury include falls on an arm that is abducted and forcefully forced overhead. Direct blows to the shoulder, forceful forced external rotation of the arm. A less common type of shoulder instability is posterior, often associated with seizures or electric shocks, when the muscles of the shoulder contract forcefully causing dislocation. What is non-traumatic instability of the shoulder? Multidirectional instability of the shoulder (MDI), also known as non-traumatic instability of the shoulder, is a loosening of the glenohumeral joint of the shoulder in multiple directions. Multidirectional instability of the shoulder develops when the ligaments around the shoulder become loose in the patient. This laxity can be a natural condition (present at birth) or can develop later in life. Many MDI patients are avid overhead athletes (e.g., gymnastics, swimming, throwing sports, baseball, tennis, etc.) who repeatedly stretch the shoulder capsule to the limits of its range of motion. These ligaments are overstretched, allowing for shoulder dislocation or subluxation, and this increased mobility leads to repeated small traumas that can be severe enough to cause a tear of the glenoid labrum or a rotator cuff tear. Patients with MDI often have other ligamentous laxities of the joint, with hyperextension of the knee and elbow being more common. These patients often suffer from bilateral MDI of the shoulder joint, and because so many athletes with MDI are very successful, there is a debate as to whether it is the joint laxity that allows these athletes to excel or the laxity caused by the repetitive pulling of the joint by athletic exercise.