progressive increase in disease in more northerly areas (maximal in scotland). some evidence suggests, at least in developed countries, more socioeconomically deprived communities have a greater risk of disease (a similar trend to diseases such as adult heart disease), though the reason for this remains unknown. one possible explanation that has been considered is tobacco smoke exposure, though this is significantly confounded by the strong socioeconomic gradient common to both smoking and perthes' disease. history 1897: the disease was first described by karel maydl (1853–1903). 1909: henning waldenström (1877–1972) described the disease, attributing it to tuberculosis. 1910: the disease was recognized as being unrelated to tuberculosis by three physicians working independently. legg–calvé–perthes is named after these three doctors: arthur legg (1874–1939), jacques calvé (1875–1954), and georg perthes (1869–1927). research directions in the uk in 2016, a nationwide study began collecting details of every case of perthes' disease as part of the british orthopaedic surgery surveillance study. this aims to get core information about the disease, prior to starting extensive clinical trials about the best forms of treatment. every hospital in england, scotland, and wales which treats perthes' disease is collecting details of new cases. this study is supported by steps charity worldwide. the study is nationally approved by the uk ethics committee and nhs research approval teams in england, scotland, and wales. the study is funded by the national institute for health and care research (nihr) and the alder hey charity. dogs lcp disease is an avascular necrosis of the femoral head in small-breed dogs, usually those weighing up to 25 lbs. lcp disease was first described in veterinary literature by tutt in 1935. tutt described the disease as almost exactly what waldenstromin (1909) described in humans. small breeds, particularly toy poodles, yorkshire terriers, pugs, jack russell terriers, west highland white terriers, and dachshunds can be affected. no sex predilection is seen in the dog as contrasted to humans, in whom an 80% male incidence of the disease is evident. similar to children, however, the condition is usually unilateral, with only about 10–15% incidence of bilateral disease. the age of onset varies between 4 and 12 months, with a peak incidence around 7 months. the pathology of avascular necrosis followed by revascularization and bony remodeling of the femoral head in the dog certainly suggests a vascular etiology, though the cause of the condition is not completely understood. hip pain is usually seen by the age of 6 to 8 months. the disease is bilateral in 12–16% of cases. x-rays are necessary to make the diagnosis and show increased opacity and focal lysis in the head of the femur, and later in the disease, collapse and fracture of the neck of the femur. the recommended treatment is surgical removal of the head of the femur, but conservative treatment (rest, exercise restriction, and pain medication) may be effective in a limited number of cases (less than 25%, according to some studies). in dogs, the prognosis is excellent with surgery. prednisolone tablets may also be helpful.