The shoulder is the most mobile joint in the body and the most unstable. That is why nature created a complex support structure to assure that the upper arm bone in stays in its socket (the rotator cuff). Instability occurs when the support structures fail to hold the upper arm bone in its place. This can happen with a traumatic injury or overuse.
Shoulder instability is common and can cause incapacitating pain and poor function. If not properly treated, it can lead to excessive mobility, repetitive partial and complete dislocations, rotator cuff tears, tendon tears and osteoarthritis.
What causes instability?
The main causes are repetitive strain and trauma. A fall that forces the arm up or abnormally rotates the shoulder can cause subluxation or dislocation, and instability.
Repetitive strain from overhead motion, like tennis, swimming and volleyball, can cause painful shoulder instability and subluxation, without dislocation or trauma. Subluxation is when the upper arm bone partially dislocates. A complication of subluxation is shoulder instability.
Dislocation is when the bone is forced completely out of its socket. A single dislocation puts the joint at risk for chronic instability and recurrent dislocations.
Both subluxation and dislocation, and excessive instability can damage the rotator cuff tissues, and stretch and tear shoulder tendons, ligaments and cartilage.
What are the symptoms?
- Pain that affects every area of life, including sleep
- Swelling and tenderness
- Weakness and numbness
- The sensation of looseness, a feeling like the shoulder is coming out of its socket.
- Subluxation and dislocation
- Apprehension or fear that the arm will come out of its socket
Who is at risk?
People who do strenuous, repetitive work involving overhead activity such as construction workers and baggage handlers are at risk.
Athletes of all ages who participate in high energy contact sports are at risk. Adolescents and young adults are most likely to suffer dislocations which increases the risk of additional dislocations.
Young athletes (adolescents and young adults) commonly suffer trauma and dislocations that result in tendons, cartilage and ligaments damage, which leads to shoulder instability. When the athlete experiences their first dislocation at a young age, there is a 70% chance of developing recurrent instability and joint dislocation. When the patient is over age 40 at the time of the first dislocation there is usually a rotator cuff tear as well; but the risk of chronic instability is significantly reduced.
How is it diagnosed?
Dr. Stark will discuss your medical history including any episodes of trauma or strain, symptoms, and instability, subluxation, and dislocations. He will conduct a physical exam to evaluate your joint and ligaments, and test for looseness with range of motion exercises. X-rays and MRI imaging may be ordered. A CT scan may also be ordered to diagnose cartilage damage.