To study the incidence of acromioclavicular joint injuries in a general population.
All acute shoulder injuries admitted to an orthopaedic emergency department were registered prospectively, using electronic patient records and a patient-reported questionnaire. The regional area was the city of Oslo with 632,990 inhabitants. Patients with symptoms from the acromioclavicular joint without fracture were registered as a dislocation (type II–VI) if the radiologist described widening of the joint space or coracoclavicular distance on standard anteroposterior radiographs. Patients without such findings were diagnosed as sprains (type I).
Acromioclavicular joint injuries constituted 11% of all shoulder injuries (287 of 2650). The incidence was 45 per 105 person-years (95% confidence interval [CI] 40–51). 196 (68%) were diagnosed as sprains and 91 (32%) as dislocations. Median age of all acromioclavicular joint injuries was 32 years (interquartile range 24–44), and 82% were men. Thirty percent of all acromioclavicular joint injuries were registered in men in their twenties. Sports injuries accounted for 53%, compared to 27% in other shoulder injuries [OR 3.1 (95% CI 2.4–4.0; p < 0.001)]. The most common sports associated with acromioclavicular joint injuries were football (24%), cycling (16%), martial arts (11%), alpine skiing and snowboarding (both 9%), and ice hockey (6%).
Our study suggests that in the general population, one in ten shoulder injuries involves the acromioclavicular joint and young men in sports are at highest risk. A prognostic level II cohort study.
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