Important normal measurements at the ankle joint:
Tibiofibular overlap should be at least 6 mm on an AP image and usually at least 1 mm on a mortise view. Reduced overlap is a sign of syndesmotic widening/injury.
Tibiofibular clear space should be less than 6 mm on both AP and mortise views. An increase in this space is a sign of syndesmotic widening/injury.
Medial clear space should less than 5 mm on both AP and mortise views. An increase in this space is a sign of deltoid ligament injury (assuming no medial malleolus fracture).