**Core Concept**
The secondary ossification centers are areas within bones where new bone tissue is formed during growth and development. The lower end of the femur, also known as the distal femur, has a specific secondary ossification center that is crucial for understanding bone growth and development in the lower limb.

**Why the Correct Answer is Right**
The secondary ossification center for the lower end of the femur is located in the epiphysis, which is the rounded end of the bone. This center is responsible for the formation of the distal femoral epiphysis, which eventually fuses with the shaft of the femur to form a single, solid bone. The development of the secondary ossification center is regulated by growth factors, including Indian hedgehog and bone morphogenetic proteins, which stimulate the proliferation and differentiation of chondrocytes within the growth plate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the secondary ossification center for the upper end of the femur, not the lower end, is located in the greater and lesser trochanters.
**Option B:** This option is incorrect because the secondary ossification center for the patella, which is the kneecap, is located in the anterior surface of the patella, not the lower end of the femur.
**Option C:** This option is incorrect because the secondary ossification center for the proximal tibia, which is the upper end of the tibia, is located in the medial and lateral condyles, not the lower end of the femur.

**Clinical Pearl / High-Yield Fact**
The timing of secondary ossification center formation is crucial for understanding bone growth and development in children and adolescents. Abnormalities in the timing or progression of ossification can lead to various bone disorders, including osteochondritis dissecans and slipped capital femoral epiphysis.

**Correct Answer:** D.