The "Double Medial Malleolus": A New Physical Finding in Talocalcaneal Coalition.

PURPOSE: It has been the observation of the senior author that there is a bony fullness or "double medial malleolus" over the middle facet as a consistent finding with most talocalcaneal coalitions (TCC). To document this observation, we reviewed records and radiographs in 3 patient groups.

METHODS: Part 1: retrospective chart review was completed for 111 feet to determine the clinical presence of a palpable "double medial malleolus." Part 2: computed tomography (CT) scans for evaluation of tarsal coalition or symptomatic flatfoot between January 2006 and December 2014 were retrospectively reviewed for the same cohort. Soft tissue thickness was measured as the shortest distance between bone and skin surface at both the medial malleolus and the middle facet/coalition. The volume of the middle facet or coalition was measured at their midpoint. These findings were compared among feet with TCC (n=53), calcaneonavicular coalition (CNC) (n=20), and flatfoot (n=38).

RESULTS: Part 1-clinical: from medical records, 38 feet (34%) had documented record of a palpable medial prominence. Of the feet reviewed with a "double medial malleolus," all had TCC (no false positives or false negatives). Clinical and CT prominence demonstrated significant correlation (rs=0.519, P=0.001). Part 2-radiographic: CT observation of "double medial malleolus" is significantly associated with TCC (P<0.001). CT observation of double medial malleolus is 81% sensitive and 79% specific as a predictive test for TCC. The middle facet-to-skin distance was significantly closer in those with TCC versus controls (P<0.001). The ratio was larger in patients with TCC versus CNC (P=0.006) or flatfeet (P<0.001). Volume was nearly twice the size in patients with TCC versus the controls (P<0.001).

CONCLUSIONS: TCCs have a bony prominence below the medial malleolus on clinical exam and CT scan not present in flatfeet or CNCs. This abnormal middle facet is almost twice the size of the normal middle facet. Obesity or severe valgus may mask this finding. If a palpable bony prominence is noted just below the medial malleolus during examination of a painful foot with a decrease in subtalar motion, the likely diagnosis is TCC. With this added clinical finding, appropriate images can be ordered to confirm the diagnosis of the latter. We advise CT scans with 3D images for surgical planning. The primary finding for tarsal coalitions in textbooks is decreased subtalar motion. This new finding of a palpable enlarged medial prominence just below the medial malleolus is highly associated with TCCs.

LEVEL OF EVIDENCE: Level III.