Genu valgus deformity occur when :
**Core Concept**
A genu valgus deformity is a condition characterized by an outward angulation of the knees, resulting in the knees caving inward. This deformity is often associated with conditions that affect the growth plates or the bones of the lower extremities.
**Why the Correct Answer is Right**
The genu valgus deformity occurs due to an imbalance in the growth rates between the medial and lateral condyles of the femur, leading to an excessive external rotation of the distal femur. This can be caused by a variety of factors, including Blount's disease, rickets, and osteogenesis imperfecta. The medial condyle grows at a slower rate than the lateral condyle, resulting in an external rotation of the distal femur and a subsequent valgus deformity.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a correct answer because it does not accurately describe the underlying cause of genu valgus deformity.
* **Option B:** This option is not a correct answer because it does not specify the exact cause of genu valgus deformity, which is related to the growth rate imbalance between the medial and lateral condyles of the femur.
* **Option D:** This option is not a correct answer because it is not a recognized cause of genu valgus deformity.
**Clinical Pearl / High-Yield Fact**
It is essential to recognize that genu valgus deformity can be a sign of underlying conditions such as Blount's disease, rickets, or osteogenesis imperfecta, which require prompt medical attention to prevent further complications.
**Correct Answer: A. Blount's disease**