Causes of Perthes Disease(Legg-Calve)
The symptoms of Legg-Calvé-Perthes disease develop due to damage to the growing portion (epiphysis) of the upper end of the thigh bone. This damage results from interruption of the blood supply (ischemia) to this region. This damages the bone-forming cells (osteoblasts) and resident bone cells (osteocytes) and results in degeneration (necrosis) and softening of the bone in this area. The upper end of thigh bone becomes fragile as bone mass is lost. It is possible that this fragile area may "fracture" internally, causing deformity. A thin line of decreased density (Caffey sign) may be apparent on the epiphysis, which may represent such a "fracture" within the bone (subchondral). Damaged bone may fragment and cause irregularities when blood flow to the affected area eventually resumes (revascularization). As the bone regrows and rehardens (re-ossifies), it may deform, resulting in permanent malformation of the upper thigh bone (e.g., abnormally flattened or unusually enlarged epiphysis).
The exact, underlying cause of the interrupted blood flow is not fully understood. Multiple factors including environmental and genetic ones may play a role in the development of the disorder. Some risk factors or conditions that may play a role in the development of LCPD include low birth weight, delayed skeletal maturity, trauma, adverse social and economic conditions, exposure to tobacco smoke, or a positive family history of the disorder. Some researchers have theorized that disorders that disrupt or affect how the blood clots (coagulation disorders) such as thrombophilia play a role in some individuals. These disorders could lead to abnormal blood clot formation would cause the interrupted blood flow that characterizes LCPD.
No one theory has been proven as the underlying or contributing cause(s) of LCPD and it is possible that different individuals may have a different underlying causes. More research is necessary to determine the complex interactions that ultimately bring about the disorder.