Shoulder pain is estimated to be present in 16% to 26% of adults. The shoulder joint is a "ball and socket" joint with a complex arrangement of tendons, muscles, bones, and ligaments, any of which can be injured.
What structures make up the shoulder joint?
The shoulder joint is made up of the following structures (see diagram below):
The three main bones of the shoulder are the humerus (arm bone), scapula (shoulder blade), and clavicle (collarbone).
The glenoid is the part of the scapula where the humerus attaches, creating the glenohumeral joint. The acromion is the part of the scapula where the clavicle attaches, making up the acromioclavicular (AC) joint, a frequently injured area.
Numerous shoulder ligaments connect bones to other bones, and shoulder tendons connect muscles to bones. In addition, there are bursae, fluid-filled sacs that cushion the shoulder.
The rotator cuff, a commonly injured area, has four different muscles (see diagram below): supraspinatus, infraspinatus, subscapularis, and teres minor.
What are some non-traumatic causes of shoulder pain?
The non-traumatic causes are varied, including issues with the glenohumeral joint, the AC joint, and the rotator cuff muscles. In addition, shoulder tendons and ligaments can be stretched, causing strains and sprains, respectively.
Referred shoulder pain occurs when the etiology (cause) of shoulder pain originates in another area and is “referred” to the shoulder. Sources of referred pain include the neck and arm muscles (biceps and triceps).
Frozen shoulder, also known as adhesive capsulitis, occurs when the body forms scar tissue around the glenohumeral joint, severely limiting the range of motion. A frozen shoulder can be idiopathic (unknown cause), follow shoulder surgery, or result from trauma.
Gout rarely affects the shoulder joint, but it has been known to occur. In bursitis, the shoulder sac fills with fluid, causing limited range of motion and pain.
What injuries are caused by trauma to the shoulder?
- Clavicular fractures are the most common type, typically occurring from a fall on an outstretched hand.
- A proximal humerus fracture occurs at the part of the arm bone closest to the shoulder. Like clavicle fractures, they can be caused by a fall on an outstretched hand but are also caused by a direct impact.
- Scapular (shoulder blade) fractures are not too common; however, they occur when there is direct trauma to the scapula or a high force impact to the middle back.
- Dislocations are common at the glenohumeral joint; a small amount of joint (synovial) fluid is present that creates negative pressure, leading to a vacuum type of condition. The humerus can dislocate (move out of position) anteriorly (forward), posteriorly (backward), or inferiorly (downward).
In addition, the AC joint can also dislocate when there is tearing of its ligaments.
What is the diagnostic workup for shoulder injury or pain?
- A history is taken to discuss daily, work, and recreational activities, including athletics.
- A physical exam checks for areas of tenderness, swelling, and warmth. In addition, there are several special tests your physician can perform to check for specific types of shoulder injuries, but they are beyond the scope of this article.
- Laboratory tests include a white blood cell level (WBCs) for infection, a rheumatoid factor for rheumatoid arthritis, and a serum uric acid for gout.
- Plain x-rays should be done to evaluate for bony abnormalities, including fractures, osteoarthritis, spurs, or osteoporosis (bone thinning).
Specific x-rays need to be done to evaluate for glenohumeral dislocation. For example, a view from the front to the back is called an A-P (anterior to posterior) view; it shows the anterior and inferior dislocations but does not allow visualization of a posterior dislocation, in which a sideways view (called a “Y” view) is required.
Computed tomography (CT) and magnetic resonance imaging (MRI) scans evaluate soft tissue structures not seen on x-rays, including the muscles, tendons, and ligaments. Nowadays, MRI is considered the “gold standard” for shoulder evaluation.
What are the treatments for shoulder dislocation and fracture?
Dislocated shoulders can be put back in place by physical force or using weights. Some cases require an intravenous (IV) muscle relaxer to relax the muscles around the shoulder before the force is applied.
Shoulder fractures may require surgery depending on the type and degree of the fracture.
What are the treatments for shoulder pain?
Once fracture, dislocation, gout, and infection are ruled out, a shoulder injury or pain can be treated like any other musculoskeletal disorder, including medications, exercises, physical therapy (PT), occupational therapy (OT), chiropractic, acupuncture, heat, ice, and injections.
However, some additional treatments are specific for shoulder injuries, discussed below:
A shoulder immobilizer can be a highly effective treatment when the shoulder is first injured. The traditional sling that goes over the neck can be used, but it is better to use the newer types that do not apply pressure on the neck.
Any shoulder dislocation needs to be followed up with an MRI to rule out any damage to the ligaments, tendons, or muscles that occur with a dislocation. In addition, exercises must be done to strengthen the shoulder muscles and prevent a recurrence of the dislocation.
The shoulder joint is made up of three bones, including the humerus (arm bone), scapula (shoulder bone), and clavicle (collarbone).
An intricate arrangement of muscles, tendons, and ligaments allows proper shoulder function.
Shoulder dislocations require x-ray evaluation with a physician placing the shoulder back in place, followed by an MRI.
Special shoulder immobilizers should be used right after a shoulder injury.
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