A 28-year-old woman presents with a painless swelling over the lateral aspect of the knee for 6 months. Radiographs reveal a lytic lesion in the epimetaphyseal region of the distal femur with a soap-bubble appearance. MRI confirms a giant cell tumor. Which of the following is the most common site of giant cell tumor of bone?

Explanation

## Most Common Site of Giant Cell Tumor ### Epidemiological Distribution **Key Point:** The distal femur (around the knee joint) is the single most common site for giant cell tumor of bone, accounting for approximately 20–25% of all cases. **High-Yield:** Giant cell tumors show a strong predilection for the **epimetaphyseal region of long bones**, particularly around the knee joint. The distribution pattern is: | Site | Frequency (%) | Location | |------|---------------|----------| | **Distal femur** | **20–25** | **Most common** | | Proximal tibia | 15–20 | Around knee (2nd most common) | | Distal radius | 10–15 | Wrist region | | Proximal humerus | 5–10 | Shoulder | | Sacrum | 5–10 | Pelvis | | Other sites | 15–20 | Rare | ### Clinical Pearl **Mnemonic — "KNEE GIANT":** Giant cell tumors favor the **K**nee region (distal femur + proximal tibia account for ~40–45% of all cases combined). The tumor typically arises in the epimetaphysis *after* physeal closure and extends to the articular surface. ### Pathological Features - Occurs almost exclusively in **skeletally mature patients** (age 20–40 years) - Presents as a lytic, eccentric lesion with a "soap-bubble" or "honeycomb" radiographic appearance - The epimetaphyseal location (extending to the subarticular cortex) is pathognomonic - Rarely occurs in the diaphysis or purely metaphyseal regions ### Why the Knee? The distal femur and proximal tibia together account for nearly half of all giant cell tumors. This predilection is thought to relate to the high metabolic activity and growth dynamics of the distal femoral and proximal tibial growth plates during skeletal maturation. [cite:Rockwood & Green's Fractures in Adults Ch 32]