The prevalence in the US is 1 in 1200 children.[1]Fisher RL. An epidemiological study of Legg-Perthes disease. J Bone Joint Surg Am. 1972;54:769-78.
http://www.ncbi.nlm.nih.gov/pubmed/5055168?tool=bestpractice.com
[2]Molloy MK, MacMahon B. Incidence of Legg-Perthes disease (osteochondritis deformans). N Engl J Med. 1966 Nov 3;275(18):988-90.
http://www.ncbi.nlm.nih.gov/pubmed/5922170?tool=bestpractice.com
The incidence varies widely internationally; it may have declined over a 19-year period in the UK among low socioeconcomic populations.[3]Perry DC, Bruce CE, Pope D, et al. Legg-Calvé-Perthes disease in the UK: geographic and temporal trends in incidence reflecting differences in degree of deprivation in childhood. Arthritis Rheum. 2012 May;64(5):1673-79.
http://www.ncbi.nlm.nih.gov/pubmed/22143958?tool=bestpractice.com
[4]Margetts BM, Perry CA, Taylor JF, et al. The incidence and distribution of Legg-Calvé-Perthes disease in Liverpool, 1982-95. Arch Dis Child. 2001 Apr 1;84:351-4.
http://www.ncbi.nlm.nih.gov/pubmed/11259241?tool=bestpractice.com
[5]Barker DJ, Dixon E, Taylor JF. Perthes' disease of the hip in three regions in England. J Bone Joint Surg Br. 1978 Nov;60-B(4):478-80.
http://www.ncbi.nlm.nih.gov/pubmed/711792?tool=bestpractice.com
[6]Mullan CJ, Thompson LJ, Cosgrove AP. The declining incidence of Legg-Calve-Perthes' disease in Northern Ireland: an epidemiological study. J Pediatr Orthop. 2017 Apr-May;37(3):e178-82.
http://www.ncbi.nlm.nih.gov/pubmed/27328117?tool=bestpractice.com
It is unclear if this trend is apparent outside the UK.
The disease appears very uncommon in black people. The incidence per 100,000 in South Africa varied between 10.8 in white people, 1.7 in those of mixed ancestry, and 0.45 in black people. South Asians have 3 times the rate of East Asians, and white people have 9 times the rate of East Asians. More northerly latitudes, independent of race, appear to have greater disease incidence.[7]Perry DC, Machin DM, Pope D, et al. Racial and geographic factors in the incidence of Legg-Calvé-Perthes' disease: a systematic review. Am J Epidemiol. 2012 Feb 1;175(3):159-66.
http://aje.oxfordjournals.org/content/175/3/159.long
http://www.ncbi.nlm.nih.gov/pubmed/22223709?tool=bestpractice.com
Typically, Legg-Calvé-Perthes disease presents in 4- to 8-year-olds with a mean age of 7 years, although it can affect children between 2 and 12 years of age. It is about 4 or 5 times more common in males than females. Legg-Calvé-Perthes disease is bilateral in about 10% to 12% of cases.[8]Hall AJ, Barker DJ. The age distribution of Legg-Perthes disease. An analysis using Sartwell's incubation period model. Am J Epidemiol. 1984 Oct;120(4):531-6.
http://www.ncbi.nlm.nih.gov/pubmed/6475922?tool=bestpractice.com