Where should the central ray be directed for an anteroposterior projection of the tibia and fibula?

Where should the central ray be directed for an anteroposterior projection of the tibia and fibula?

• A. Proximal tibia near the knee
• B. Mid-shaft of the tibia/fibula
• C. Distal tibia near the ankle
• D. At the level of the knee joint

Answer: (C)

When imaging the tibia and fibula in an AP projection, center the central ray to the midpoint of the leg, at the midshaft of the tibia between the knee and ankle. The beam should be perpendicular to the leg so the tibia is evenly magnified and both joints are included in the image. Directing the ray toward the distal tibia near the ankle tends to shift the center of the exposure away from the proximal tibia and knee, leading to poor visualization of those areas and increased distortion. By targeting the midshaft, you get a well-centered image with uniform detail along the length of the tibia and fibula. Ensure the leg is straight, the knee and ankle are in a true AP position, and the foot is dorsiflexed so the ankle is perpendicular to the IR.

When imaging the tibia and fibula in an AP projection, center the central ray to the midpoint of the leg, at the midshaft of the tibia between the knee and ankle. The beam should be perpendicular to the leg so the tibia is evenly magnified and both joints are included in the image. Directing the ray toward the distal tibia near the ankle tends to shift the center of the exposure away from the proximal tibia and knee, leading to poor visualization of those areas and increased distortion. By targeting the midshaft, you get a well-centered image with uniform detail along the length of the tibia and fibula. Ensure the leg is straight, the knee and ankle are in a true AP position, and the foot is dorsiflexed so the ankle is perpendicular to the IR.