Physical therapy in Murray for Shoulder

Welcome to FYZICAL Salt Lake City's patient resource about Shoulder Instability.

Shoulder instability means that the shoulder joint is too loose and is able to slide around too much in the socket. In some cases, the unstable shoulder actually slips out of the socket. If the shoulder slips completely out of the socket, it has become dislocated. If not treated, instability can lead to arthritis of the shoulder joint.

This article will help you understand:

• what parts of the shoulder are involved
• what causes shoulder instability
• what treatments are available

What parts of the shoulder are involved?

The shoulder is made up of three bones: the scapula (shoulder blade), the humerus (upper arm bone,) and the clavicle (collarbone).

Shoulder Bones

The rotator cuffconnects the humerus to the scapula.

The rotator cuff is actually made up of the tendons of four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis.

Tendons attach muscles to bones. Muscles move bones by pulling on tendons. The muscles of the rotator cuff also keep the humerus tightly in the socket. A part of the scapula, called the glenoid, makes up the socket of the shoulder. The glenoid is very shallow and flat. A rim of soft tissue, called the labrum, surrounds the edge of the glenoid, making the socket more like a cup. The labrum turns the flat surface of the glenoid into a deeper socket that molds to fit the head of the humerus.

Surrounding the shoulder joint is a watertight sac called the joint capsule. The joint capsule holds fluids that lubricate the joint. The walls of the joint capsule are made up of ligaments. Ligaments are soft connective tissues that attach bones to bones. The joint capsule has a considerable amount of slack, loose tissue, so that the shoulder is unrestricted as it moves through its large range of motion. If the shoulder moves too far, the ligaments become tight and stop any further motion, sort of like a dog coming to the end of its leash.

Dislocations happen when a force overcomes the strength of the rotator cuff muscles and the ligaments of the shoulder. Nearly all dislocations are anterior dislocations, meaning that the humerus slips out of the front of the glenoid. Only three percent of dislocations are posterior dislocations, or out the back.

Dislocations

Sometimes the shoulder does not come completely out of the socket. It slips only partially out and then returns to its normal position. This is called subluxation.

Related Document: A Patient's Guide to Shoulder Anatomy