Understanding Shoulder Instability

The shoulder joint is considered one of the most elegant joints in the human body because it has tremendous range of motion. But being the most mobile joint in the body also come with a price: it undergoes tremendous stress and is also the most common joint to be dislocated.

Shoulder instability simply means that the shoulder joint is too loose and slides around too much in its socket. In most cases, the shoulder slips and causes discomfort, but in some instances it may slip completely out of the joint and become dislocated.

What makes up the shoulder joint?

The shoulder is made up of 3 bones: the humerus (upper arm bone), the scapula (shoulder blade) and the clavicle (collarbone). The head of the humerus forms the ball of the shoulder joint while part of the scapula (glenoid) forms the socket.

The glenoid is shallow and flat, like a golf tee, allowing the humerus head to slip out easily. This is prevented by a rim of soft tissue called labrum. The labrum surrounds the edge of the glenoid, hence deepening the socket so that it molds and fits the head of the humerus. Encasing the humerus head and the glenoid is a watertight sac called the capsule. The capsule holds the fluid which lubricates the joint. The wall of this sac is made up of ligaments. Ligaments are soft connective tissues that attach bone to bone. There are various ligaments which tighten at different position of the arm so that they can confer stability without restricting movements.

There are also muscles surrounding this capsule called the rotator cuff muscles. This group of muscles confers dynamic stability to the shoulder joint. This means that when they contract they will encourage the humerus head to sit in the glenoid. However if they are weak, injured or fatigue, then this ability is compromised.

Click [here] to find out more.