Understanding a Shoulder Injury – Part 1
With today’s post we are going to take a closer look at what can go wrong with the shoulder and start to define some of the common medical terms you may hear that are used to describe a shoulder injury.
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:
- The structures of the joint
- 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.
July 1st, 2009 at 7:25 am
[...] Part 1 of Understanding a Shoulder Injury we discussed what structures in the shoulder joint can become injured. In Part 2 we will discuss [...]