Ankle Fractures

15-20 degrees internal rotation of the leg to parallel the intermalleolar axis with the X-ray beam. This provides a true AP view of the ankle mortise and allows accurate measurement of clear spaces.

Clear-space measurements detect talar shift, but the commonest correctable error is a shortened or malrotated fibula, and you must know the specific checks that confirm an anatomic fibular reduction (a short/externally-rotated fibula is the classic cause of a malreduced, arthritis-prone ankle):

• Talocrural angle: the angle between a line perpendicular to the tibial plafond and a line through the two malleolar tips; normal is about 83 degrees (within a few degrees of the uninjured side). A reduced angle indicates fibular shortening.
• The "dime sign" / ball sign (Shenton line of the ankle): on the mortise view there is a smooth, unbroken curve between the recess in the lateral talar process and the tip of the lateral malleolus (like a coin fitting into the contour). A break/step in this arc means the fibula is short (the curve no longer matches) - the single best quick check for fibular length.
• Tibiofibular line / equal clear spaces: the medial, superior and lateral clear spaces should be equal and symmetric; the subchondral bone of the plafond and medial malleolus should form a continuous line into the fibula.
• Rotation: compare the fibular contour and the talocrural angle to the contralateral (template) ankle intra-operatively; loss of the normal fibular twist or an abnormal incisura position signals malrotation.

Exam point: confirm fibular reduction by an intact dime/ball sign, a talocrural angle of about 83 degrees matching the other side, and symmetric clear spaces - a broken dime arc means the fibula is short and must be re-reduced before fixation.

The classic "fix if over 25% of the articular surface" threshold is increasingly questioned. Modern thinking favours fixing based on syndesmotic stability, fragment morphology (Bartonicek/Haraguchi classification) and articular step, not size alone - because even small fragments carrying the PITFL can restore syndesmotic stability when fixed.

The morphology classifications named above are themselves examinable, because fragment shape (not just size) now drives the decision to fix and the approach:

Haraguchi (CT-based, 3 types):

• Type I - posterolateral-oblique: the commonest; a triangular posterolateral fragment.
• Type II - medial-extension (transverse): the fracture extends across to the medial malleolus (a posteromedial component) - higher chance of an intra-articular die-punch fragment.
• Type III - small-shell: a small avulsion shell off the posterior rim.

Bartonicek/Rammelt (CT-based, 5 types, emphasises the fibular notch/incisura and stability):

• Type 1: extra-incisural fragment (rim only, intact notch) - stable.
• Type 2: posterolateral fragment extending into the incisura.
• Type 3: posteromedial two-part fragment (involving the medial malleolus).
• Type 4: large posterolateral triangular fragment (over a third of the notch).
• Type 5: irregular osteoporotic fragment.

Why it matters: fragments involving the incisura (Bartonicek 2-4) are the ones whose fixation restores syndesmotic stability via the attached PITFL and improves articular congruity - so a CT to characterise the fragment, and posterior (posterolateral or posteromedial) buttress fixation of an incisura-involving fragment, is preferred over a stand-alone syndesmosis screw.

Exam point: classify the posterior malleolus on CT - Haraguchi I/II/III by location and Bartonicek 1-5 by incisura involvement - and fix the incisura-involving fragments to restore both the joint surface and syndesmotic stability.

Q: Which structure is the primary restraint to lateral talar shift? A: The deep deltoid ligament (specifically the deep tibiotalar fibers). The superficial deltoid resists eversion. Disruption of the deep deltoid allows the talus to shift laterally, increasing medial clear space.

Q: A Weber B fracture is defined by the fibula fracture being at what level? A: At the level of the syndesmosis. This correlates with partial syndesmosis injury potential. Weber A is below (intact syndesmosis), Weber C is above (disrupted syndesmosis).

Q: What is the upper limit of normal for medial clear space on a mortise view? A: 4mm (or equal to superior clear space). Greater than 4-4.5mm suggests deltoid ligament rupture and indicates an unstable injury requiring surgical management.

Q: What is the effect of 1mm lateral talar shift on tibiotalar contact? A: 42% reduction in contact area. This is the basis for emphasis on anatomic reduction - even small amounts of talar shift dramatically increase contact pressures and accelerate post-traumatic arthritis.

Q: At what level should a syndesmosis screw be placed above the joint line? A: 2-4cm above the joint line, parallel to the tibial plafond. Some surgeons prefer 3-4cm to minimize risk of articular damage. Screw directed 25-30 degrees anterior to coronal plane.