Martin R. Coleman, MD
The shoulder joint is the most complex joint system in the human body. It has many components that work together to ensure it functions smoothly when we call upon it to do everyday tasks. It is also the most mobile joint in the body and because of that it also has the potential to be the most unstable.
A “ball and socket” joint, the shoulder joint is comprised of the head, or upper end, of your humerus (the bone the runs between your shoulder and elbow), which is the “ball.” This is generally round which allows it to rotate easily. The “socket” is a mostly flat portion of the shoulder blade (scapula) called the glenoid. This means that round head is sitting on a flat surface, much like a baseball balancing on a plate, meaning that it is very unstable. Picture instead the baseball sitting in a bowl, which would be far more stable. The flat bone surface of the glenoid has a thick cartilage area known as the labrum around the entire rim, converting the plate into a bowl. A healthy, intact labrum helps to stabilize the joint, but if it is damaged, the ball can slide off the glenoid toward the location of the tear. If you think of this as a clock face, tears around twelve o’clock, known as SLAP tears, (Superior Labrum Anterior to Posterior) allow the ball to move upward and pinch the rotator cuff. Tears in the area of four to six o’clock can lead to either a subluxation, where the ball temporarily slides forward or backward without completely falling off the plate, or a dislocation, where the ball is completely off the plate and will not easily be maneuvered back in place by the patient.
The support structures around the shoulder are made up of ligaments, tendons including the Rotator Cuff, and other muscles, which combine to keep pressure on the joint to keep it in place. Tears or weakness in these soft tissue elements can make the joint more unstable.
When we injure our shoulder in a traumatic accident or overuse it repetitively in sports or during work, one or more of these essential components can break down. An individual may even be born with a bone abnormality or genetic issue that makes their soft tissue weaker and overly flexible. These conditions can make instability more likely. Instead of staying securely in place, the shoulder joint may become unstable and subluxate or dislocate due to weakness in the muscles, or looseness in the tendons and ligaments that serve as the support system to hold the shoulder joint in place. Once a subluxation or full dislocation happens, chances are greater that it will happen again, especially if the first episode occurs when the patient is under twenty years old. Over time, and if not treated, these repeat dislocations can lead to chronic shoulder instability. Unfortunately, repeated episodes of instability will damage the cartilage of the joint, resulting in irreversible arthritis. In some cases young people with multiple dislocations are found to have severe arthritic damage to the shoulder joint resulting in potential lifelong problems.
Some patients even have what we call multidirectional instability, where the ball can move downward, forward and backward, and is very difficult to treat.
Many young patients have slight looseness in the joint, leading to pain and anxiety because there can be constant worry that the joint cannot be trusted. We refer to this as “low-level instability” and we are frequently able to resolve these symptoms without surgery. Some patients with these borderline cases will actually outgrow the condition because the soft tissue around the joint stiffens as we get older.
When a patient comes in to see me for a consultation, I will order x-rays, and perform a thorough physical exam. We will discuss the details about their shoulder, including their daily activities and lifestyle, the timing and causes of their pain, and previous treatments. After gathering all of that information, I will design a treatment plan specifically for them.
We typically start with a conservative (non-surgical) plan. The patient will try a program of physical therapy to strengthen and stabilize their shoulder muscles, including the rotator cuff and the muscles around the shoulder blade known as scapular stabilizers. We try to resolve muscle imbalance which can be present even in patients who seem to have good shoulder strength. Therapy will include what we call modalities, such as ice and heat, ultrasound and massage. We typically use anti-inflammatory medication to help to ease the pain of the therapy.
Many patients who work hard, follow the regimen, and have patience, will see dramatic improvements and can be treated conservatively. Others with more severe, persistent instability may only improve with surgery. We generally have to consider surgery if there is no improvement after two months of physical therapy with an expert therapist.
One shoulder subluxation or dislocation, especially in adult patients, can frequently be treated conservatively. We start with rest, possibly with a sling, and progress to exercises for range of motion and strengthening, often with the help of a physical therapist.
My next article will discuss treatment options if this approach does not work.