Commonest age of Perthes disease is:
**Core Concept**
Perthes disease, also known as Legg-Calve-Perthes disease, is a childhood hip disorder characterized by temporary loss of blood supply to the femoral head, leading to avascular necrosis. It predominantly affects children between the ages of 4 and 10 years.
**Why the Correct Answer is Right**
The commonest age of Perthes disease is around 5 years, with a peak incidence between 4 and 8 years. This is due to the fact that the growth plates in the femur are still open, allowing for some degree of remodeling and healing. The disease is more common in boys than girls, with a male-to-female ratio of approximately 4:1. The exact cause of Perthes disease is unknown, but it is thought to be related to a combination of genetic and environmental factors.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Perthes disease typically affects children between 4 and 10 years, not infants under 1 year.
**Option B:** This option is incorrect because while Perthes disease can occur in older children, the peak incidence is between 4 and 8 years, not in late childhood or adolescence.
**Option C:** This option is incorrect because Perthes disease is a childhood disorder, not a condition that affects adults in their 30s or 40s.
**Clinical Pearl / High-Yield Fact**
Perthes disease often presents with hip pain, limited mobility, and a limp in children. Early diagnosis and treatment can help prevent long-term complications, such as hip deformity and arthritis.
**Correct Answer: B. 5 years.**