Muscles
The shoulder relies on many muscles to function properly. These include the muscles that stabilize and move the shoulder blade, the muscles that stabilize the arm bone within the shoulder joint (also known as the Rotator Cuff muscles) and the muscles that move the arm.

Any of these muscles can become injured through a sprain, strain or tear and therefore cause pain and/or the shoulder to function improperly.

One particular muscle in the shoulder that is especially susceptible to injury is the Supraspintus. It is one of the Rotator Cuff muscles.

It is a small muscle that travels from above the bony protrusion (or spine) of the shoulder blade, through a tunnel of bone and ligaments and attaches to the arm bone.

It is susceptible to injury when the arm bone doesn’t rotate precisely within the shoulder joint. This excess movement can cause pinching of the muscle between the arm bone and the shoulder blade. This is what is commonly referred to as Shoulder Impingement.

Tendonitis
A simple way to think of a muscle is a spring attached to a rope. The spring represents the muscle belly; this is where the shortening, lengthening and production of force comes from.

The tendon is more like the rope. A muscle will turn into tendon prior to attaching into a bone.

The tendon is responsible for transferring the force produced by the muscle belly to the bones for either movement or stability.

Tendonitis refers to inflammation of the tendon. In other words something is irritating the tendon causing it to swell and be painful.

Bursitis
A bursa is a small fluid filled sac that typically lies between a tendon and the bone. Its purpose is to prevent the tendon rubbing directly on the bone.

It too can become irritated, inflamed, and painful.

That concludes the two posts about Understanding a Shoulder Injury. If you have further questions please feel free to leave a comment.

These terms include: rotator cuff tear/strain, labrum tear, adhesive capsulitits, bursitis, impingement, arthritis, separated shoulder, dislocated shoulder, and tendinitis

As discusses in previous posts, the shoulder has many moving parts. To better understand these parts and what can go wrong let’s break things down in to two categories:

1. The structures of the joint
2. The structures that surround the joint

Structures of the shoulder joint include the bones, cartilage, labrum, joint capsule, and ligaments.

The structures around the joint include the muscles, tendons, and bursa.

Let’s start by looking at the structures of the shoulder joint that can commonly be injured.

Labrum
The majority of movement of the shoulder occurs between the arm bone and the shoulder blade. Click here to see shoulder joint post for more information about shoulder anatomy.

You may remember the golf ball and golf a tee analogy, where the golf ball represents the top of the arm bone, the golf tee represents the shoulder blade portion of the shoulder joint.

This bony structure allows great flexibility and movement in the shoulder. Unfortunately it doesn’t provide much stability.

The body’s ingenious design to increase stability of the shoulder while allowing mobility is called the labrum.

The labrum is a ring of fibrocartilage that runs around the cavity of the glenoid fossa (i.e. the golf tee). It basically makes the joint surface deeper so that the bones fit better together.

Since the labrum is fibrocartliage and not bone it make it more susceptible to injury or tearing. Damage to this structure compromises the stability of the shoulder joint.

Common types of labrum tears include SLAP and Bankhart.

Arthritis
There are over 100 different types of arthritis; some of the well known types include Rheumatoid, Psoriatic, and Osteoarthritis. These can all affect the shoulder joint.

Cartilage is typically found where bone meets bone in a joint. Cartilage is like padding for the end of a bone. The cartilage prevents bone rubbing directly on another bone.

The easiest way to think of Osteoarthritis, a common diagnosis of shoulder pain, is wear and tear of the cartilage.

To illustrate this further consider if you drove your car for 60 000 miles, you are going to have wear on your tires. If you’re tires are out of alignment you will have greater wear on some areas of the tire compared to other areas.

The body reacts in a similar way, if you use it for 50-60 years there is going to be wear and tear of some of the joints and thus osteoarthritis.

Separated Shoulder
A separated shoulder refers to an injury of the AC joint (acromionclavicular). This is the place where the collar bone connects to the shoulder blade.

These bones are held together with ligaments and joint capsule.

An impact to this area can cause a sprain or tear of the ligaments.

Dislocated Shoulder
This is similar to the separated shoulder but refers to the arm bone.

An impact can sprain or tear the ligaments and joint capsule that connect the arm bone to the shoulder blade, thus causing the arm bone to pop out of its socket.

Adhesive Capsulitis
Adhesive Capsulitis is more commonly known as frozen shoulder.

The joint capsule is basically a sac that surrounds a joint.

Due to the shoulders great flexibility the joint capsule has the capacity to extend and stretch in many directions.

When it is at rest, i.e. arm by the side, there are small folds in the capsule.

Sometimes these folds can become stuck together thus preventing stretching and extensibility of the capsule during movement. This can be very painful.

This concludes Part 1 of Understanding a Shoulder Injury. Part 2 will go in to greater detail of what structures around the shoulder joint can become injured.