The age of the patient is the single most important factor in determining the etiology of hip and pelvis pain. In very young children, there is rarely a significant acute injury, but several common orthopedic entities involving this region may initially present with exercise-associated pain. As a child grows, skeletal development occurs in a predictable pattern with the appearance of apophyses and epiphyses and their eventual fusion. During growth, these are areas of relative weakness, and avulsion injuries to the developing apophyses are more common than those involving the musculotendinous unit. During adolescence, ossification continues, but the immature skeleton remains more prone to injury as the high physical demands of sports participation exceed the capacity of the musculoskeletal system. Additionally, rapid increases in muscular power related to hormonal changes accentuate the mismatch between muscular and physeal strength.

In children and adolescents, the most common disorder that causes hip pain is transient synovitis . In addition, Legg–Calve–Perthes disease has been shown to have an incidence of 1.5–5 per 10,000 children of ages 2–12 years. Slipped capital femoral epiphysis , with an incidence of 0.8–2.2 per 10,000, is also an oft-encountered etiology for hip pain that usually presents in the early adolescent period. Developmental hip dysplasia, noted in 1.5–20 cases per 1000 births in developed countries, depending on the diagnostic modality used and timing of the evaluation, may lead to hip pain later in life [2]. Each entity should be considered not only in the investigation of hip pain in the limping child, but also in complaints of knee pain in this population. Each is discussed further in this text. (Please see Chap. 7—Hip and Pelvis Injuries in Childhood and Adolescence.)

The epidemiologic data regarding incidence of hip and pelvis injury in children have been studied at length, often in association with investigation of injury incidence at other anatomical sites. Data have been further divided into acute and chronic injury , with acute injury occurring much more commonly in this population. In retrospective studies, injuries to hip and thigh in children encompassed 17–25 % of all acute, but only 2.2–4.8 % of chronic injuries [7]. Sports injuries to the hip and groin have been noted in 5–9 % of high school athletes [1, 5].

Investigation involving primary school through high school-aged individuals in the general population has found an incidence of hip pain in 6.4 % [2]. This can be further divided into 4 % in the primary school-aged population, compared with 7.8 % in the high school group. These data portend a higher risk in the older child of suffering from hip pain. Interestingly, in the same study, 2.5 % of the subjects were found to have clinical evidence of hip pathology on examination, the most commonly noted findings being pelvic obliquity, limb length discrepancy, and snapping hip. In only 0.6 % of those who reported hip pain was any pathology noted by a physician on physical examination. This may suggest that objectively dysfunctional hips are relatively common in the school-aged and adolescent population, but that these pathologic features do not typically result in pain. One may further conclude that most hip pain in this population is functional, as examination findings are typically lacking in those who do report pain.

Among adults , the spectrum of hip and pelvis injury evolves. As these patients age, the risk of pain from hip osteoarthritis increases substantially. The prevalence of hip and pelvis pain in adults from all etiologies ranges from 2.8 % to 22.4 %, and reports of pain tend to increase with age [2]. In the athletic population , increased age is a risk factor for players of field-based sports in sustaining a groin or hip injury, likely due to decreased elasticity of collagen tissue in older individuals [8, 9].

Over the age of 60, fully 14.3 % of adults report significant activity-limiting hip pain [10]. This has an effect beyond the bothersome joint, as those who suffer from hip pain have poorer self-rated overall health scores, as well as increased knee and back pain and reduced muscle power. Climbing/descending stairs and walking tend to elicit the most severe pain [11]. Morning stiffness is also common in the older population with hip pain, affecting 30 % of those reporting hip pain [11].

Participation in athletic activity of any kind has been shown to increase the risk of hip and pelvis injury, as well as the eventual development of hip osteoarthritis [12]. Men with high long term exposure to sports had a relative risk of developing hip osteoarthritis of 4.5 when compared to those with lower exposure [12]. In those with exposure to high physical loads from both sports and occupation, the relative risk increased to 8.5 for the development of hip osteoarthritis when compared to those with low physical loads in both activities [12].