An ALPSA lesion is an injury at the front of the shoulder

Shoulder

The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...

 associated with shoulder dislocation.

Anatomy

The shoulder joint is made up of the glenoid

Glenoid cavity

The glenoid cavity is a shallow pyriform, articular surface, which is located on the lateral angle of the scapula. It is directed laterally and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest.This cavity forms the...

 and humeral head. The humeral head is ball shaped but the glenoid is more dish shaped than cup shaped. To aid stability of the joint, the glenoid has a soft tissue

Soft tissue

In anatomy, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body, not being bone. Soft tissue includes tendons, ligaments, fascia, skin, fibrous tissues, fat, and synovial membranes , and muscles, nerves and blood vessels .It is sometimes...

 bumper around its edge (the labrum) which acts as a bumper preventing dislocation of the head from the glenoid.

Pathology

The anterior (front) labrum can peel off the glenoid resulting in a Bankart lesion

Bankart lesion

In orthopaedics, a Bankart lesion is an injury of the anterior glenoid labrum due to repeated shoulder dislocation. When this happens, a pocket at the front of the glenoid forms that allows the humeral head to dislocate into it...

. When the periosteum

Periosteum

Periosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of all bones....

 (fibrous tissue surrounding bone) peels off as well this is called an ALPSA lesion. When this happens the labrum (bumper) falls away and rolls up. It normally falls medially and downwards.

Surgery

If required, the labrum and periosteum can be reattached, recreating the bumper affect, aiding shoulder stability and hopefully preventing further dislocation. It can be done by keyhole or open surgery. The injury cannot always be repaired.