This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well.

The acromioclavicular (AC) joint is located between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle.

[citation needed] The rotator cuff is a structure composed of tendons that, with associated muscles, holds the ball at the top of the humerus in the glenoid socket and provides mobility and strength to the shoulder joint.

[2] Four filmy sac-like structures called bursa permit smooth gliding between bone, muscle, and tendon.

Problems seen with a dislocated shoulder are tearing of the ligaments or tendons reinforcing the joint capsule and, less commonly, nerve damage.

Doctors usually diagnose a dislocation by a physical examination, but X-rays are taken to confirm the diagnosis and to rule out a related fracture and other complications.

[citation needed] Doctors treat a dislocation by putting the head of the humerus back into the joint socket (glenoid fossa) of the scapula—a procedure called manipulation and reduction.

After pain and swelling have been controlled, the patient enters a rehabilitation program that includes exercises to restore the range of motion of the shoulder and strengthen the muscles to prevent future dislocations.

[citation needed] After treatment and recovery, a previously dislocated shoulder may remain more susceptible to reinjury, especially in young, active individuals.

[citation needed] Sometimes the doctor performs surgery through a tiny incision into which a small scope (arthroscope) is inserted to observe the inside of the joint.

After this procedure, called arthroscopic surgery, the shoulder is generally restrained by a sling for three to six weeks, while full recovery, including physical therapy, takes several months.

When ligaments that hold the AC (acromioclavicular) joint together are partially or completely torn, the outer end of the clavicle may slip out of place, preventing it from properly meeting the scapula.

After a period of rest, a therapist helps the patient perform exercises that put the shoulder through its range of motion.

[citation needed] The "rotator cuff" is a group of four tendons that blend together as they attach to the upper end of the arm bone (humerus).

These tendons transmit the force of muscles originating on the shoulder blade (scapula) to the arm providing rotational motion and centering or stability of the joint.

[7][8][9][10] A group of respected scientists wrote in a review of existing evidence that, the theory that this degeneration is related to pinching (or impingement) between the head of the humerus and the acromion is now considered inaccurate.

[11] The process can involve the intra-articular part of the long head of biceps in addition to the supraspinatus, infraspinatus, and subscapularis tendons.

Sports involving overuse of the shoulder and occupations requiring frequent overhead reaching are other potential causes of irritation to the rotator cuff or bursa and may lead to inflammation and impingement.

Ultrasound scans are frequently used to confirm a suspected tendinitis or bursitis as well as rule out a tear in the rotator cuff muscles.

Impingement syndrome may be confirmed when injection of a small amount of anesthetic (lidocaine hydrochloride) into the space under the acromion relieves pain.

If there is still no improvement after six to 12 months, the doctor may perform either arthroscopic or open surgery to repair damage and relieve pressure on the tendons and bursae.

[citation needed] Symptoms include a dull ache deep in the shoulder joint, trouble sleeping due to the instability and discomfort, and extreme weakness in overhead activities.

This condition, which doctors call adhesive capsulitis, is frequently caused by injury that leads to lack of use due to pain.

There is also a lack of synovial fluid, which normally lubricates the gap between the arm bone and socket to help the shoulder joint move.

[citation needed] When a fracture occurs, the doctor tries to bring the bones into a position that will promote healing and restore arm movement.

[citation needed] In the case of rheumatoid arthritis, specific medications selected by a rheumatologist may offer substantial relief.

[citation needed] When exercise and medication are no longer effective, shoulder replacement surgery for arthritis may be considered.

In this operation, a surgeon replaces the shoulder joint with an artificial ball for the top of the humerus and a cap (glenoid) for the scapula.

The success of the operation often depends on the condition of rotator cuff muscles prior to surgery and the degree to which the patient follows the exercise programme.

The most common surgical treatment, known as resection arthroplasty, involves cutting a very small portion off the clavicle end and letting scar tissue fill in its place.