Ankle fracture and mortise injury

X-ray · CT

Draft this report · X-ray Draft this report · CT

First and second year — the floor first, then every step

Read the ankle as a ring around the talus: find every malleolar fracture, then measure the mortise — medial clear space, tibiofibular clear space and overlap — because a widened mortise makes a simple-looking fibular fracture unstable.

Orient first

The mortise is a ring: the tibial plafond and both malleoli, bound by the deltoid ligament medially, the lateral ligaments and the syndesmosis. Two breaks in the ring make it unstable, and a ligament rupture counts as a break.
The level of the fibular fracture relative to the syndesmosis (Weber) predicts syndesmotic injury: below it (A) rarely, at it (B) sometimes, above it (C) usually.
A medial malleolar fracture or medial clear space widening with no fibular fracture at the ankle — examine the proximal fibula (Maisonneuve).

Acquire the study

AP, MORTISE (about 15–20° internal rotation) and lateral views; weight-bearing or stress views where the protocol uses them to judge stability.

The manoeuvre

Mortise view: MEDIAL CLEAR SPACE between the medial malleolus and the talus at the level of the talar dome — compare with the superior clear space.
AP view: TIBIOFIBULAR CLEAR SPACE and TIBIOFIBULAR OVERLAP, measured 1 cm above the plafond.
Fibula: level of the fracture relative to the syndesmosis/plafond, orientation (spiral from anteroinferior to posterosuperior is supination–external rotation).
Medial malleolus: transverse (avulsion) versus vertical (impaction) fracture line.
Lateral view: posterior malleolus fragment — its height and displacement; talar subluxation.
Talar dome for an osteochondral lesion; the base of the fifth metatarsal and the anterior calcaneal process on the included field.

What confirms it

Instability is a bimalleolar or trimalleolar fracture, OR a fibular fracture with medial clear space widening (deltoid rupture), OR syndesmotic widening.

What licenses you to exclude it

A normal non-weight-bearing mortise does not exclude a deltoid or syndesmotic injury in a Weber B fracture; stress or weight-bearing views, or MRI, answer it — say which your centre uses.

The classic misread

Measuring the medial clear space on the AP rather than the mortise view.
Missing a proximal fibular fracture — if the medial side is injured without a lateral ankle fracture, image the whole fibula.

Reporting the injury

Classification to use

Danis–Weber A/B/C (fibular level relative to the syndesmosis) and/or Lauge-Hansen (mechanism: SER, SA, PER, PA) — state which. AO/OTA 44 if used.

Measurements — and how to take them

Medial clear space on the mortise view at the level of the talar dome: > 4 mm, or greater than the superior clear space, is abnormal (commonly used thresholds — verify).
Tibiofibular clear space 1 cm above the plafond: > 6 mm abnormal on AP and mortise.
Tibiofibular overlap 1 cm above the plafond: < 6 mm on AP (or < 1 mm on mortise) abnormal.
Posterior malleolar fragment as a percentage of the tibial articular surface on the lateral or sagittal CT (fixation thresholds of about 25–33% have been used; many surgeons now decide on fragment morphology and syndesmotic stability — verify).

What to report

Each fracture: fibula (Weber level, orientation), medial malleolus, posterior malleolus (size), plafond.
Medial clear space, tibiofibular clear space and overlap with their values; talar shift.
Osteochondral lesions and associated fractures (fifth metatarsal base, calcaneal anterior process, proximal fibula).

How to report it

X-ray: "Weber B spiral fracture of the distal fibula at the level of the syndesmosis. Medial clear space 7 mm, wider than the superior clear space of 3 mm, indicating deltoid ligament injury and lateral talar shift. Tibiofibular clear space 5 mm. Small posterior malleolar fragment."

What not to report

Do not describe the mortise as "congruent" without the measurements when there is a fibular fracture.

Associated injuries to look for

Maisonneuve fracture (proximal fibula), osteochondral lesion of the talar dome, fifth metatarsal base and anterior calcaneal process fractures, Lisfranc injury.

What changes management

Medial clear space widening or syndesmotic widening with a fibular fracture — operative fixation (the fracture is unstable).
Bimalleolar and trimalleolar fractures; large or displaced posterior malleolar fragments; talar subluxation.

Reference values

Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.

Diagnostic criteria

Ankle · Medial clear space
up to about 4 mm, and equal to the superior tibiotalar clear space
Mortise view of the ankle (15–20° internal rotation). The distance between the lateral border of the medial malleolus and the medial border of the talus, at the level of the talar dome.
Widening indicates deltoid ligament disruption and an unstable injury — the finding that turns an isolated fibular fracture into a surgical one. ⚠️ A NORMAL NON-STRESSED FILM DOES NOT EXCLUDE IT; gravity or weight-bearing stress views exist for exactly this question.
X-ray
Ankle syndesmosis · Tibiofibular overlap and clear space
overlap above about 6 mm on AP / 1 mm on mortise; clear space under about 6 mm
AP and mortise ankle radiographs, measured 1 cm proximal to the tibial plafond.
⚠️ HIGHLY ROTATION-DEPENDENT and with wide normal variation, so comparison with the uninjured side is more reliable than any absolute figure — and CT is more sensitive than radiography for syndesmotic diastasis.
X-ray
Ankle (fibular fracture) · Weber / AO-Danis fibular level
a named level: Weber A below the syndesmosis, B at the syndesmosis, C above — the syndesmosis-overlap entry is the companion measurement
Height predicts syndesmotic injury risk; it does not replace looking at the medial clear space (already registered).
X-ray
Ankle (injury pattern) · Lauge–Hansen mechanism (SER / PER / SA / PA)
the four mechanisms are supination-external rotation (SER, commonest), pronation-external rotation (PER), supination-adduction (SA) and pronation-abduction (PA). Each predicts a ligament-then-bone sequence. Complementary to Weber A/B/C, not a competing millimetre
If you cannot assign a pattern confidently, say so and use Weber plus the registered clear-space / overlap measurements.
X-ray
Ankle (talar tilt) · Talar tilt on stress views
commonly quoted as under about 10°, or under 5° of difference against the contralateral ankle — published thresholds genuinely vary
AP mortise view under varus (inversion) stress: the angle between the tibial plafond and the talar dome articular surfaces.
⚠️ Stress radiography is examiner-dependent and increasingly replaced by ultrasound and MRI of the ligaments — quote the tilt with the technique used, and prefer the side-to-side difference to any absolute figure.
X-ray

See it on real cases

Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.

Key papers

Reviews and guidelines from RSNA, ESR and related journals. Each opens at its DOI.

Simplified diagnostic algorithm for Lauge-Hansen classification of ankle injuries ↗Okanobo H, Khurana B, Sheehan S, et al. · RadioGraphics 2012RSNA · PubMed
Distal Tibiofibular Syndesmosis: Anatomy, Biomechanics, Imaging Approach, and Postoperative Evaluation ↗Silva LNMD, Morimoto LR, Watanabe GG, et al. · RadioGraphics 2026RSNA · PubMed
Imaging in syndesmotic injury: a systematic literature review ↗Krähenbühl N, Weinberg MW, Davidson NP, et al. · Skeletal Radiology 2018ISS · PubMed
The concept of ring of injuries: evaluation in ankle trauma ↗Nicolai C, Bierry G, Faruch-Bilfeld M, et al. · Skeletal Radiology 2022ISS · PubMed