Most people consider the shoulder to be a "ball and socket" joint, but it is not that simple. The shoulder is the most complicated joint in the body.
The most common shoulder injury is a strain
which involves damage to the muscles and tendons that connect to the bone and contract to move the joint.
An injury to the soft tissue that holds the joint together or stabilizes the join is called a sprain
. the "ball and socket" glenohumeral joint has a labrum or lip of cartilage, that surrounds the flat socket and helps it conform to the round ball.
The Superior Labrum from Anterior to Posterior may pull off with its attached biceps tendon. This is called a SLAP Lesion
, and is both a strain and a sprain. This can occur when the tightened tendon is pushed against by the humeral head, ripping the tendon off with its labral attachment.
A bursa is a loose sack or collection of tissue that functions to decrease friction. Such tissue may exist between the rotator cuff and acromion in youth, but wears out by the time you are 20 years old; if you are a swimmer, it can wear out before you are ten. We may not have been designed to do a lot of overheard reaching. Subacromial bursitis
is wear of the rotator cuff under the acromial bone and
Joints have friction free surfaces of shock absorbing cartilage that allow normal motion. if this surface is injured by impact, immobility, infection or just wearing out, it becomes as rough as sandpaper and motion becomes more difficult. Stiffness develops and it is usually painful.
A broken bone is called a fracture, which, in the shoulder, most commonly occurs in the collarbone.
Pain and motion loss in moving the shoulder is related to inflammation and/or build up of scar tissue, and is called a frozen shoulder. It is primary if it affects all motions and secondary if it affects only certain motions. It can be due to scar filling the inside of the joint called arthrofibrosis; thickening and shortening of the joint capsule referred to as adhesive capsulitis; or build up of scar under the acromion and deltoid muscle know as subdeltoid fibrosis. It may be a combination of each.