Could failure of the spring ligament complex be the driving force behind the development of the adult flatfoot deformity?

We conducted an investigation into the relative associations of magnetic resonance imaging (MRI)-defined pathologic features of the spring ligament and/or tibialis posterior tendon with radiographic evidence of a planovalgus foot position. A total of 161 patient images (MRI and plain radiographs) obtained from the foot and ankle clinic (2008 to 2011) were retrospectively reviewed. All 161 patients (64 male and 97 female; mean age 45.9 years, range 18 to 86) were included in the analysis. Lateral weightbearing radiographs were analyzed for the talo-first metatarsal angle ≥ 5°, calcaneal pitch ≤ 20°, and talocalcaneal angle ≥ 45°. A positive finding for ≥ 1 measurements identified a radiographic planovalgus position of the foot. The radiographic deformity was analyzed against the MRI evidence of either spring ligament or tibialis posterior tendon pathologic features for significance (p < .05). Evidence of a spring ligament abnormality was strongly associated with a planovalgus foot position, reaching high levels of statistical significance in all 3 categories of radiographic deformity (odds ratio 9.2, p < .0001). Abnormalities of the tibialis posterior tendon failed to demonstrate significance, unless grade I changes were excluded, and grade II and III appearances were analyzed in isolation (odds ratio 2.9, p = .04). Although absolute causal relationships were not tested, this investigation has clearly demonstrated that MRI-defined abnormalities of the spring ligament complex are possibly of at least equal importance to tibialis posterior dysfunction for the presence of a moderate to severe radiographic planovalgus foot position.