Procedures · Lower Extremity

Tibia and Fibula Positioning Series

Explore the tibia and fibula's anatomy, then use Practice mode to position the AP and lateral projections yourself.

Tibia and fibula

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The routine tibia and fibula series

The projections this region is examined with. Set them up yourself in Practice positioning.

Anteroposterior projection · lower leg

Demonstrates: The whole lower leg — tibia and fibula side by side, with the proximal fibula partly overlapped by the tibia — and both the knee joint and the ankle joint included.
Part position: Supine, with the pelvis, knee and leg adjusted into a true AP with no rotation — the femoral condyles lie parallel to the image receptor and the foot is vertical. Dorsiflex the ankle to 90° to the lower leg where the patient tolerates it. Both the ankle and the knee joint sit 1–2 inches (2.5–5 cm) inside the ends of the receptor, so divergent rays cannot throw either joint off it; if the limb is too long for that, the leg goes on diagonally.
Central ray: 90° to the image receptor, centered to the midpoint of the lower leg.
Why it is positioned this way: A long bone is centred to its own midpoint rather than to a palpable landmark, and the receptor is chosen long enough that the knee and the ankle both appear. That is the criterion the exam is built around: an injury to one bone of the lower leg is commonly paired with one at the other end, so an image that shows only one joint cannot rule the other out.

Mediolateral projection · beam enters medial, exits lateral

Demonstrates: The lower leg in profile with the tibia and fibula lying on top of one another rather than side by side, again with both the knee and the ankle joint included.
Part position: Lateral recumbent, injured side down, with the opposite leg placed behind the affected leg. The leg is in a true lateral — the plane of the patella sits at 90° to the image receptor. Both the ankle and the knee joint again sit 1–2 inches (2.5–5 cm) inside the ends of the receptor.
Central ray: 90° to the image receptor, centered to the midpoint of the lower leg.
Why it is positioned this way: The beam enters the medial surface and exits the lateral, which is what makes this a mediolateral projection rather than a lateromedial one. The superimposition is the tell: on any frontal projection the two bones sit side by side, so whether they overlap separates a lateral from an AP at a glance.