SLAP is an acronym for "Superior Labral tears, Anterior to Posterior."  SLAP lesions are tears of the superior labrum that spans front to back.  These can occur from a downward blow to the forward elevated arm, a direct fall onto the shoulder, motor vehicle accident, overuse, repetitive throwing, and many others.  There is a high association with partial-thickness rotator cuff tears (supraspinatous).

The labrum is a piece of cartilage that runs around the outside of the glenoid socket, acting like a bumper to keep the humeral head centered into the glenoid.  A tear of the labrum results in instability, giving the sensation of a "dead arm" or like it "comes out of place."  Pain usually results in the shoulder and can easily be misdiagnosed as tendonitis, biceps pain, or AC pain.  These tears are missed over 50% of the time with a simple MRI and requires a MR arthrogram to approriately diagnose these tears (93% sensitivity).  Physical therapy can often help strengthen the rotator cuff to compensate from the tear and associated instability.  When this fails, arthroscopic shoulder surgery can repair these tears to restore function and to relieve pain.