Mechanisms of Shoulder Injury

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| Home | Rotator Cuff | Shoulder Separation and Dislocation | Cartilage | References |

Shoulder Separation and Dislocation

There are two main joints that make up the shoulder, both of which are susceptible to acute injury brought on by direct trauma to the shoulder. Sport related causes for these two distinct injuries are intuitively trauma related. Any direct blow to the shoulder can result in either separation or dislocation. Full contact sports such as football, lacrosse and wrestling have the highest incidence of such injuries. However, a simple fall on the shoulder can have similarly detrimental effects. Competetive cycling is a sport that has a high risk of a fall directly on the shoulder.

www.juneauempire.com/images/ 081503/football.jpg

Glenohumeral Joint

The Glenohumeral joint is the ball and socket joint between the head of the humerus and the glenoid. Separation of these two joints is broken down into two categories of severity. If the joint separates partly on temporary basis, it is referred to as subluxation. If the joint completely separates and remains so, the injury is a dislocation.

While the actual instance of dislocation is usually associated with acute trauma, subluxation may occur sans trauma in athletes with weak, unstable or imbalance rotator cuff muscles. In such cases of atraumatic instability, the athlete can lose control of his/her muscles, and the shoulder joint can sublux intermittently. As discussed before, any sport with an overhead action makes athletes susceptible to rotator cuff weakness. Athletes with weak rotator cuffs are more susceptible to recurring atraumatic injury to the GHJ.

Recurrence

A shoulder dislocation further weakens the rotator cuff, and puts the athlete at a very high risk of recurrence. As reported by the American Journal of Sports Medicine, the reported rate of shoulder instability recurrence has reached 100% for skeletally immature patients and as high as 96% for adolescents and adults younger than 30 years of age . Also, athletes that have atraumatic subluxation are more vulnerable to a GHJ dislocation, if subjected to intense trauma. Lacrosse players and football quarterbacks are most vulnerable, as they often have weak rotator cuffs, and are constantly subjected to traumatic incidents.

Treatment

Although most doctors try to avoid surgery by treating patients with physical therapy, cortozone shots, and strengthening exercises, the incidence of recurrence greatly decreases after surgery. Looking toward the future, hopefully a full shoulder replacement will enable athletes to return to full strength (or better), but current technology (see interview, joint replacement) does not allow sufficient mobility or strength to return to competitive sports.

Acromioclavicular Joint

The acromioclavicular joint is the place at which the acromion meets the clavicle. Injury to the joint occurs when the two bones separate, resulting in a ligament sprain or, in more severe cases, tear. The injury is commonly known as “shoulder separation.”

Simple AC joint injuries are broken down into three grades of increasing severity:

I. Supporting ligaments are stretched.
II. Partial tear in supporting ligaments.
III. Complete tear of supporting ligaments.

In the most severe cases, the end of the clavicle protrudes beneath the skin, and is visible as a prominent bump. While shoulder separation can heal, most patients show long term effects of mild pain and lack of mobility.

Treatment

In severe cases of shoulder separation, surgery is necessary for rehabilitation. While many doctor save it as a last resort, patients that have pain and or deformity in the joint after several months of conservative require surgical intervention.

When the AC joint is affected, there is often a corollary injury to the coracoacromial ligaments. To decide whether surgery is indicated, AC joint injuries are further classified into one of six groups (see chart + picture side and below). AC refers to the acromioclavicular joint, and CC refers to the coracoacromial ligament.

http://www.orthoteers.co.uk/Nrujp~ij33lm/Orthshouldacj.htm (Picture and Chart)

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Created by: Blair Smith, Connie Lee, Daniel Solomon, Matthew Whitson and Stephanie Chang
Date last modified: 5/2/2004