The epidemiology and demographics of hip dysplasia

Abstract

The etiology of developmental dysplasia of the hip (DDH) is unknown. There are many insights, however, from epidemiologic/demographic information. A systematic medical literature review regarding DDH was performed. There is a predominance of left-sided (64.0%) and unilateral disease (63.4%). The incidence per 1000 live births ranges from 0.06 in Africans in Africa to 76.1 in Native Americans. There is significant variability in incidence within each racial group by geographic location. The incidence of clinical neonatal hip instability at birth ranges from 0.4 in Africans to 61.7 in Polish Caucasians. Predictors of DDH are breech presentation, positive family history, and gender (female). Children born premature, with low birth weights, or to multifetal pregnancies are somewhat protected from DDH. Certain HLA A, B, and D types demonstrate an increase in DDH. Chromosome 17q21 is strongly associated with DDH. Ligamentous laxity and abnormalities in collagen metabolism, estrogen metabolism, and pregnancy-associated pelvic instability are well-described associations with DDH. Many studies demonstrate an increase of DDH in the winter, both in the northern and southern hemispheres. Swaddling is strongly associated with DDH. Amniocentesis, premature labor, and massive radiation exposure may increase the risk of DDH. Associated conditions are congenital muscular torticollis and congenital foot deformities. The opposite hip is frequently abnormal when using rigorous radiographic assessments. The role of acetabular dysplasia and adult hip osteoarthritis is complex. Archeological studies demonstrate that the epidemiology of DDH may be changing.

Figure 1

Ultrasound neonatal hip examination. (a) A representative longitudinal ultrasound image of a normal neonatal hip. The ilium is marked by the asterisk, the bony acetabular roof by the large arrowhead, and the abductor muscles seen by the longitudinal white/gray alternating structures. (b) Measurement of the alpha (α) and beta (β) angles on ultrasound establish the Graf class. The baseline is first drawn and is the line along the ilium as it intersects the bony and cartilaginous portions of the acetabulum (solid black line). The α angle is the angle between the baseline and the roof of the bony acetabulum; the β angle is the angle between the baseline and the cartilaginous roof. (c) An example of a Graf IIc hip, with an α angle of 43° and a β angle of 49°. (d) An example of a Graf IV hip, irreducible dislocated hip, with an α angle of 42°. Typically β angles are not measured on dislocated hips, but in this example it would measure 99°.

Figure 2

The incidence of DDH in various ethnic groups. (a) The incidence of DDH in indigenous populations. (b) DDH incidence in Indo-Mediterraneans. (c) DDH incidence in Indo-Malay peoples. (d) DDH incidence in all Caucasians. (e) DDH incidence in Eastern European Caucasians. (f) Incidence of DDH amongst all ethnic groups; note the y-axis is logarithmic₁₀.

Figure 3

Variability in DDH demographics amongst ethnic groups. (a) Variability in gender amongst ethnic groups. (b) Variability in unilateral/bilateral involvement amongst ethnic groups. (c) Variability in right and left hip involvement amongst ethnic groups.

Figure 4

(a) The prevalence of DDH in the late 1970's by age group in the Sámi living in northern Finland, Lake Inari region. The overall prevalence was 16.3; for those ≥60 years of age it was 60.2, and dropped to 3.5 for those 0–19 years of age. This has been attributed to a decrease in the practice of newborn swaddling using the gietka or komse. Data from Eriksson et al. [324]. (b) The marked decrease in DDH incidence in Japan after introduction of a nationwide educational program for both neonatal hip instability and hip dislocation after 3 months of age. For neonatal hip instability the data was taken from [84, 325] and for hip dislocation from [–90].

Figure 5

The demographics of hip osteoarthritis in adults. (a) Radiographic prevalence of hip osteoarthritis by ethnicity and geographic location. Data from Lau et al. [472]. (b1) Estimated rates of total hip replacements for primary coxarthrosis in San Francisco, 1984–1988, for men. Data from Hoaglund et al. [473]. (b2) Estimated rates of total hip replacements for primary coxarthrosis in San Francisco, 1984–1988, for women. Data from Hoaglund et al. [473]. (c) Differences in the etiology of adult hip arthritis between Japanese and Caucasian patients. Note the rarity of SCFE and Perthes' as a cause of adult hip arthritis. Data from Hoaglund et al. [474].