Acromioclavicular joint instability

Abstract

Acromioclavicular (AC) joint injuries are common and account for about 12 % of all shoulder injuries in clinical practice. This number increases to almost 50 % in athletes participating in contact sports. The true prevalence might even be underestimated since many individuals with low-grade (type I or II) injuries may not seek medical attention. A recent longitudinal cohort study reported on an incidence of 9.2/1,000 injuries among young athletes, whereas male patients experienced a significantly higher incidence rate than female patients. This is most likely due to a different risk-taking behavior and contact sports rather than anatomic differences between genders. The most AC joint injuries occur in the third decade, and the sports most likely to contribute to the incidence of AC joint dislocations are football, soccer, hockey, rugby, biking, and skiing. The mechanism of trauma is frequently a direct blow to the shoulder with the arm in an adducted position. Due to the excessive strength of the sternoclavicular joint, the AC joint and the clavicle represent the weak points for injury.