In general the incidence rate is defined as the number of new events occurring during a specified time period divided by the number of people at risk [8].

Dynamic variation of the incidence rate of proximal humerus fractures has been described by several authors between 1965 and 1989 [9] (see Fig. 1.2). Horak et al. showed an overall incidence rate of 56/100,000 [10], Kjær et al. described a rate of 69/100,000 [11] and Lind et al. reported an incidence rate of 73/100,000 per year. Current epidemiologic studies refute a further increase, presenting an incidence rate of 63/100,000 in 2006 [3] and 61/100,000 in 2008 [12]; this slight decrease might be due to improvements in prophylaxis on falling, progress in medical treatment of osteoporosis, more careful behavior of the elderly or even more active older patients.

Humerus fractures are generally divided into three anatomic regions: proximal, mid-shaft and distal humerus fractures. In an epidemiologic study in the United States the proximal humerus was identified as the most common site of fracture accounting for approximately 50 % of humerus fractures [12] (Fig. 1.3). The distal humerus with approximately 35 % accounted for the next most common site, whereas mid-shaft fractures occurred in only 15 %. A relevant impact of gender in terms of a female to male ratio was only found for the proximal region accounting for 2.3:1, whereas a ratio of 1.3:1 resulted for the humeral shaft, and of 0.9:1 for the distal humerus. In general the fracture location depends on the trauma mechanism and other patient-specific risk factors: in this context proximal humerus fractures are associated with an increased age, female gender and osteoporotic bone, compared to distal humerus fractures, which are associated with children’s age.

Fractures of the proximal humerus are seen most commonly in the elderly population [13, 14] with an average age accounting for approximately 65 years [3, 4, 9]. Incidence and severity of the fracture increase with the patient‘s age (Fig. 1.4) [4]. Especially in female patients the incidence increases exponentially at an age of 40 years and older. In contrast, male patients show an increased incidence in the youth, however, at an age of 50 years and older, women’s incidence predominates [15, 16]. These gender differences might be due to lower bone mineral density and a correspondingly higher prevalence of osteoporosis in women than in men [17].

The chief cause of proximal humeral fractures is a simple fall onto the upper extremity with over 90 % happening in patients older than 60 years [4, 18], while only a few fractures are caused by traffic accidents or accidents at work [9]. In people younger 60 years of age most accidents happen in public, whereas in people older 60 years of age more than half of the accidents occur at home (see Table 1.1). Activity at the time of the accident is mainly walking straight ahead [18]. According to the patient’s own judgment the main reason for the injury is tripping or slipping. In 76 % the main impact of the fall is directed straight to the shoulder or upper arm resulting in a concomitant subcutaneous hematoma at that particular site. Most of the patients report that they had fallen obliquely forward or to the side. Accumulation of accidents in the colder months (Fig. 1.5) [4, 9] is due to snow and ice on the streets as well as early darkness. The majority of accidents happens during the middle of the day, although a peak in incidence is recognizable before midnight (Fig. 1.6) [9].