Epidemiology of Isolated Acromioclavicular Joint Dislocation

Background. Acromioclavicular (AC) joint dislocation is a common shoulder problem. However, information about the basic epidemiological features of this condition is scarce. The aim of this study is to analyze the epidemiology of isolated AC dislocation in an urban population. Materials and Methods. A retrospective database search was performed to identify all patients with an AC dislocation over a 5-year period. Gender, age, affected side and traumatic mechanism were taken into account. X-rays were reviewed by two of the authors and dislocations were classified according to the Rockwood’s criteria. Results. A total of 108 patients, with a mean age of 37.5 years were diagnosed with AC dislocation. 105 (97.2%) had an isolated AC dislocation, and 3 (2.8%) were associated with a clavicle fracture. The estimated incidence was 1.8 per 10000 inhabitants per year and the male-female ratio was 8.5？:？1. 50.5% of all dislocations occurred in individuals between the ages of 20 and 39 years. The most common traumatic mechanism was sport injury and the most common type of dislocation was Rockwood type III. Conclusions. Age between 20 and 39 years and male sex represent significant demographic risk factors for AC dislocation. 1. Introduction Acromioclavicular (AC) joint dislocation is one of the most common shoulder problems accounting for 9% of all shoulder injuries [1–3], in particular during sport activities which involve contact [4–8]. AC joint dislocations can result from both direct and indirect trauma. Direct trauma is caused by a vertically oriented superior impact on the lateral part of the shoulder, forcing the AC joint in an inferior direction [9]. Indirect trauma generally results from falling on an adducted and outstretched arm causing the humeral head to be driven into the inferior aspect of the acromion and the joint itself [10]. The severity of this condition is directly related to the force of impact. AC joint dislocations range from a simple sprain of the acromion-clavicular and coraco-clavicular ligaments, which are responsible of holding the joint in its physiological position without displacement, to widely displaced injuries with dislocations of the distal third of the clavicle after the delta-trapezial fascia [10]. AC dislocations are classified on the basis of the radiographic findings. Different classification systems are available [11, 12], being that of Rockwood et al. [12] the most widely utilized (Table 1). Table 1: The Rockwood classification takes into account not only the acromioclavicular joint, but also the coracoclavicular ligament,