Hindfoot Alignment Valgus Moment Arm Increases in Adult Flatfoot with Achilles Tendon Contracture

Abstract

Adult acquired flatfoot is often associated with Achilles tendon contracture and may be associated with isolated spring ligament insufficiency without Achilles tendon contracture. We have studied the hypothesis that standing valgus hindfoot alignment moment arm is increased in adult acquired flatfoot with Achilles tendon contracture when compared to adult acquired flatfoot without Achilles tendon contracture. The standing hindfoot alignment, standing lateral tibial-calcaneal angle, lateral talo-first metatarsal angle, lateral medial cuneiform arch height, and anteroposterior talonavicular coverage angle were measured in 22 patients with a clinical diagnosis of adult acquired flatfoot with one foot with clinical Achilles tendon contracture and one without that diagnosis. We compared the adult acquired flatfoot group to a control group of 15 patients with no foot or ankle deformities or previous foot or ankle surgeries. In patients with flatfoot and Achilles tendon contracture, there was a significantly increased valgus hindfoot alignment, talo-first metatarsal angle, talonavicular coverage angle, tibiocalcaneal angle and a decreased arch height when compared to the control group. In all flatfeet, we found an increased tibiocalcaneal angle. In both flatfoot groups, an increasing tibiocalcaneal angle and an increasing talo-first metatarsal angle was correlated to a decreasing arch height. In adult acquired flatfoot without Achilles tendon contracture diagnosed by clinical exam, an increasing talonavicular coverage angle was correlated to an increasing talo-first metatarsal angle and a decreasing arch height. Adults with flatfoot and Achilles tendon contracture have a significantly increased standing hindfoot valgus alignment moment arm and other associated deformities.