Incidence of Midfoot Instability Associated With Medial Malleolus Fractures: A Retrospective Cohort Study

The incidence of secondary medial arch instability (talonavicular and first ray instability) associated with medial malleolus fractures has not been totally quantified, and to date, its contribution to poor foot function is unknown.

Twenty-five patients with various mechanisms of ankle injuries associated with medial malleolus fractures who underwent surgical treatment were assessed for patient demographics, mechanism of injury, type of fracture and quantity of medial malleolus displacement in X-rays prior to surgery, type of fixation, and level of midfoot instability, assessed by determining and quantifying talonavicular laxity and first ray instability.

In rotational ankle fractures with the medial malleolus involved, increased midfoot laxity and first ray instability were present in injured ankles compared to the uninjured (p<0.05). In non-rotational ankle fractures (supination adduction/supination plantar flexion), affected feet also had a mean increase in lateral translation scores and first ray instability scores but without statistical significance (p>0.05). There was no significant difference in the spring ligament thickness between injured and uninjured feet (p>0.05), and the displacement of the medial malleolus was not a predictor for the development of increased talonavicular laxity (p>0.05).

Ankle fractures with medial malleolus fractures have a significantly higher incidence of medial arch instability. Rotational ankle injuries, arising from supination external rotation and pronation injuries, can significantly affect medial arch stability. We advocate that surgical restoration of superficial deltoid-spring/capsular-ligamentous integrity and/or early post-operative orthotics after medial malleolar fractures may protect the first ray destabilization and preserve future foot function.