How to perform a C-arm projections - ankle fracture surgery
Source
Surgeon:
Lasse Rämö (orthopedic surgeon)
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Summary
Focus: Standard C-arm projections used in ankle fracture surgery to evaluate fracture alignment and ankle joint congruence.
Key elements: Direct AP, mortise, lateral projections, and external rotation stress testing with assessment of medial clear space.
In ankle fracture surgery, three standard projections of the ankle joint are used to evaluate the fracture itself and especially the ankle joint congruence. The talus, tibial plafond, lateral malleolus, and medial malleolus should form a symmetrical joint.Direct AP projection
Mortise projection
Lateral projection
Step-by-Step Technique
Direct AP Projection
Used to assess the overall congruence of the ankle joint in neutral position.
The ankle joint is kept at 90-degree dorsiflexion.
A direct AP projection is taken with the C-arm perpendicular to the ankle joint.
In an AP projection, the fibula overlaps the tibia and talus. Therefore, precise analysis of the ankle joint congruence can’t be made, but you can coarsely assess the congruence.
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Mortise Projection
Key projection for assessing the ankle joint congruence, as you can visualize the whole joint space from this projection.
Keep the C-arm perpendicular to the ankle joint.
Inward rotate the tibia and the foot by about 15–20 degrees while maintaining the 90-degree dorsiflexion of the ankle.
An ankle joint is congruent when, in mortise projection, the talus, tibial plafond, lateral malleolus, and medial malleolus form a symmetrical joint.
In a congruent ankle joint, with an intact syndesmosis and deltoid ligament, the talus should not shift laterally, causing widening of the medial clear space (MCS).
External Rotation Stress Test
External rotation stress test is used to test the congruence of the ankle joint under stress.
Obtain the above-described mortise projection and then externally rotate the foot by using moderate force while keeping the tibia in internal rotation.
If the talus moves laterally in external rotation stress test, it increases the space between the medial border of the talus and the medial malleolus (medial clear space, MCS).
An MCS of over 5 mm is considered significant, and surgical treatment of an ankle fracture should be considered. However, a calibrated picture should be in use when assessing MCS.
Lateral Projection
To obtain clear visualization of the posterior triangle (posterior malleolus), lateral view of the tibial plafond, and talar dome to evaluate the ankle-joint congruence in the lateral view.
The C-arm is perpendicular to the ankle joint in the horizontal plane.
The ankle joint is kept in 90 degrees dorsiflexion and internally rotated by about 15–20 degrees.
The joint surface between the tibial plafond and talar dome should be symmetrical and congruent.
The talus should not be shifted either anteriorly or posteriorly relative to the tibial plafond
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Piftalls and Complications
FAQ
What standard C-arm projections are used in ankle fracture surgery?
The standard projections are direct AP projection, mortise projection, and lateral projection.
What is the mortise projection used for?
The mortise projection is the key projection for assessing ankle joint congruence because the whole joint space can be visualized from this projection.
How is the mortise projection obtained?
Keep the C-arm perpendicular to the ankle joint and inward rotate the tibia and foot by about 15–20 degrees while maintaining 90-degree dorsiflexion of the ankle.
What does widening of the medial clear space indicate during external rotation stress testing?
If the talus moves laterally during the external rotation stress test, it increases the space between the medial border of the talus and the medial malleolus, known as the medial clear space.
What medial clear space measurement is considered significant?
An MCS of over 5 mm is considered significant, and surgical treatment of an ankle fracture should be considered. A calibrated picture should be in use when assessing MCS.
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