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Understanding Shoulder Separation And Dislocation

Ruzanna Harutyunyan's picture
Understanding Shoulder Separation And Dislocation

For many individuals, a diagnosis of shoulder instability - either a shoulder separation involving the acromioclavicular (AC) joint or a shoulder dislocation of the glenohumeral (GH) joint - can initially result in some confusion. Making distinctions between these conditions and gaining a better understanding of the complex nature of the shoulder can help explain both diagnosis and treatment options.

The shoulder is actually made up of four different articulations or joints: the AC joint, where the acromion (the upper portion of the scapula) meets the collarbone or clavicle; the glenohumeral joint, where the humerus (the large bone in the upper arm) joins the glenoid, the cup-like structure on the scapula; the sternoclavicular joint, where the clavicle meets the sternum; and the scapulothoracic articulation where the scapula meets the thoracic (chest) wall.

Together these articulations make up what physicians refer to as the “shoulder girdle.” A network of ligaments (which act as static, immobile stabilizers), muscles (which act as dynamic, moving stabilizers) and other soft tissue supports these joints and hold them in proper alignment.

“Movement in this part of the body is more complex than in other large joints, such as the hip or knee. Each time the arm is raised, not only does the ball of the humerus move in the socket of the glenoid, but the clavicle and the acromion rotate 40 degrees with respect to one another, while the scapula moves on the chest wall,” explains Frank A. Cordasco, MD, MS, an associate attending orthopaedic surgeon at Hospital for Special Surgery (HSS).

A healthy shoulder allows a wide range of motion that encompasses activities of everyday living as well as athletics. Shoulder instability is diagnosed when some type of injury affects the complex of bones and soft tissues. It may occur as the result of a single trauma or as the result of a series of microtraumas (smaller injuries that accumulate over time). The most commonly occurring injuries to the shoulder are those involving the acromioclavicular (AC) joint and the glenohumeral (GH) joint.

Shoulder Separation—the AC Joint

Shoulder separation describes the condition in which the ligaments connecting the AC joint are injured and the acromion begins to move away from the clavicle. Because the injury is a disruption in the suspensory mechanism that keeps the arm suspended from the clavicle and close to the chest, it can be very disabling. Many patients with a shoulder separation develop the problem during athletic activity, but shoulder separation can also result from accidents such as falling on the tip of the shoulder.

Shoulder separation occurs along a spectrum of progressive injury, ranging from a sprain or partial tear of the ligaments making up the least severe type of separation, to a complete tear of the major ligaments that support the joint, resulting in more severe injury or separation.

Orthopedists use the Rockwood classification system—a numerical scale from Type I to VI—to help define their diagnosis, which is made on the basis of physical examination as well as x-ray. A Type I injury indicates minimal injury or sprain of the AC joint, while more severe injuries are indicated by a higher number, Type VI being the most severe.

Treatment of shoulder separation depends on a number of factors, including the severity of the separation, the patient’s age, and their willingness and ability to modify their activities. Among competitive or elite athletes - including those at the high school or collegiate level - treatment decisions are also guided by whether the problem arises pre-, during, or post-season. Athletes who are mid-season may be treated non-operatively (depending upon their sport and position) so that they may continue participating in their sport, then opt for surgical treatment in the off-season.

Treatment Options

Types I-II:

Lower grade shoulder separations (Types I and II) are usually treated non-operatively, with initial rest followed by a course of physical therapy to maintain flexibility and range of motion and to strengthen surrounding muscles.

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Type III:

While Types I and II comprise partial separation, Types III and above are complete separations. Patients with a Type III shoulder separation represent a group for whom the choice of treatment may be somewhat more controversial.

“Traditionally, patients with these injuries may have undergone non-operative treatment, but today we tend to recommend surgical repair for a complete AC separation, based upon the patient’s age and activity level,” says Dr. Cordasco. Although a patient with this type of shoulder separation may feel better in six to eight weeks after the injury, the long-term effects of the higher grade separation may become problematic.

“Because the acromion drops down, the mechanics of the muscles that are functioning to move the arm are altered. With ten, fifteen, or twenty years of repetitive motion, there will be more wear of the rotator cuff muscles, and tendons,” he says. Patients may develop a condition known as secondary impingement syndrome, which is characterized by pain, weakness, and loss of motion.

In patients with Type III separations, age is a significant consideration. “In a 20-year-old, we assume the patient is going to live for another 50 or 60 years,” says Dr. Cordasco. “When I see a young patient who’s going to remain active, I often recommend surgical treatment.” However, he adds, patients seeking treatment at their community hospital, where newer techniques are potentially unavailable, may not be offered this option. Conversely, in a patient in his or her “middle years” who is willing to alter his or her activities, non-operative treatment may be appropriate.

Types IV-VI:

Patients with separations that are graded as types IV, V, and VI are usually advised to undergo surgical treatment to repair ligament injury, a procedure that may be performed either with an open incision or with the aid of arthroscopy. In arthroscopic surgery, the orthopaedic surgeon is able to repair the injury using miniaturized instruments inserted in the shoulder through small incisions. A small camera inserted through another incision helps guide the procedure. “My preference is to perform the procedure using an arthroscopic approach which we devised here at the Hospital for Special Surgery” says Dr. Cordasco.(1,2)

Repair of the ligaments requires a graft from another location, which may be in the form of an autograft (obtained from the patient) or an allograft (obtained from a cadaver).

“Completely torn ligaments will not heal on their own,” Dr. Cordasco explains,” the goal of surgery for shoulder instability is to restore the anatomy by reconstructing the ligaments. Doing so gives you the optimum outcome. Attempts to alter the anatomy are not as successful.”

In the past, surgeries to repair shoulder separation often involved transfer of tissue to support the joint; these efforts met with variable outcome and had a higher failure rate, as well as other long-term problems.


Surgical treatment of shoulder separation has a high success rate, with long-term results of arthroscopic procedures showing comparable results to those of traditional open surgery. However, experts concur, in the short-term, that arthroscopic treatment is more comfortable for the patient and has a shorter recovery period associated with it. Arthroscopic surgery is not an option for all patients, including those who are undergoing revision surgery for an injury that was not treated successfully in the past.

Interestingly, patients with less severe forms of AC separation may be at greater risk for developing the long-term complication of AC arthritis. This is due to the disruption of the joint surfaces that occurs with the injury that may, over time, result in erosion of the articular cartilage or joint cushion, and subsequent “wear and tear” arthritis. In untreated type III, IV, V, and VI separations, other long-term complications may ensue, but because there is no contact of the joint surfaces, the risk of developing separation-related arthritis is absent.

Frank A. Cordasco, MD, MS
Associate Attending Orthopaedic Surgeon, Hospital for Special Surgery
Associate Professor of Orthopaedic Surgery, Weill Cornell Medical College

Reprinted from www.hss.edu



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