How much rotation from an AP position of the ankle is typically required to produce an AP mortise projection?

• A. 5-10 degrees
• B. 10-15 degrees
• C. 15-20 degrees
• D. 20-25 degrees

Answer: (C)

To create an accurate AP mortise projection of the ankle, a specific degree of rotation is essential to visualize the joint space between the tibia, fibula, and the tarsal bones. Typically, a rotation of 15 to 20 degrees from the anteroposterior (AP) position is required. This degree of rotation allows the fibula to move slightly away from the tibia within the image, effectively positioning the talofibular joint in the central part of the radiograph.

Achieving this rotation helps to open the mortise joint, giving better visualization of the entire ankle joint, particularly the lateral and medial malleoli. This projection is crucial in evaluating joint integrity and any potential pathology, such as fractures or dislocations. The necessity of the 15 to 20 degrees of rotation over other values is based on both anatomical considerations and practical imaging techniques to optimize the clarity of the joint space.