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By Dr. Gavin Webb, Wentworth Health Partners Seacoast Orthopedics & Sports Medicine

The shoulder joint has the greatest range of motion of any joint in the body. It allows the arm to move in many directions. But with this mobility comes the potential of instability.

Anatomy of the shoulder

The shoulder joint is made up of three different bones: humerus (upper arm) scapula (shoulder blade) and clavicle (collarbone). Unlike the hip joint which has a deep socket that provides stability, the shoulder socket (glenoid) is very shallow and much of the stability in the shoulder joint comes from the soft tissues and muscles. A dislocation is when the ball (humeral head) comes all the way out of the socket. This usually requires someone else to put it back into place. When the ball slips part of the way out and back in, that is called a subluxation.

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Photo courtesy of

What causes shoulder instability?
Dislocations usually result from sudden trauma that forces the ball out of the socket. This can happen from a fall onto the arm or if the arm is forced into certain positions. This can result in a tear in the labrum, the soft tissue bumper around the socket. Once the labrum is torn, the shoulder is much more likely to dislocate and this can lead to chronic instability which can damage the cartilage and lead to early onset arthritis. There are some connective tissue disorders that can make shoulders more unstable and sometimes subluxations can occur without any trauma.

What are the symptoms?
Shoulder dislocations are extremely painful and need to put back into place as soon as possible. Sometimes a dislocation causes numbness and weakness from nerves being stretched. After the ball is put back into the socket, the pain usually improved quickly, but the shoulder may continue to feel like it is slipping out of place or that it can’t be trusted. Sometimes there is ongoing pain from a labral tear.

How is it diagnosed?
A dislocation is usually confirmed by X-rays, which are repeated once the ball is back in the socket to make sure there are no fractures. Often times an MRI with dye injected into the shoulder or a CT scan may help to confirm the diagnosis and identify other problems.

How is it treated?
Because a lot of stability in the shoulder comes from the muscles, physical therapy can be very helpful to increase strength and decrease instability. PT is the primary treatment for non-traumatic instability and usually requires several months of exercises. However, when a traumatic dislocation causes a labral tear (Bankart tear), this requires surgery to repair the labrum and tighten up the shoulder. This is often done arthroscopically with a camera and small incisions. After surgery the shoulder is immobilized in a sling at first and then PT is started to regain range of motion and maximize strength prior to returning to full activities.

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What do I need to know?
• Contact and overhead sports have the highest rates of shoulder instability
• If left untreated, shoulder instability can cause permanent damage
• Keeping your shoulder strong and flexible can help prevent instability
• If you are having shoulder problems, it is best to be evaluated by a specialist


About Dr. Webb: Treating conditions affecting the shoulder and knee, Dr. Webb has a special interest in sports medicine and the prevention and treatment of athletic injuries in patients of all ages. He has conducted research and lectured on cartilage injuries and presented papers at national and international meetings. He has expertise in cartilage restoration procedures and alternatives to total knee replacement surgery in younger patients.

Dr. Webb is board-certified in orthopedic surgery with subspecialty certification in sports medicine and a team physician for the UNH Wildcats.

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