Hindfoot Moment Arm and Pes Planovalgus Radiographic Parameters in the Adult Acquired Flatfoot and Normal Patient Populations
INTRODUCTION: The use of the hindfoot moment arm in the radiographic assessment of pes planovalgus (flatfoot) deformity is well described in the literature and commonly used for surgical planning of deformity correction. No study to the authors’ knowledge has investigated the relationship between the hindfoot moment arm and other common pes planovalgus radiographic parameters in both the normal patient population and those with pes planovalgus. This concept is important because in the setting of an increased hindfoot moment arm, the choice of surgical procedure for pes planovalgus deformity correction may change. PUROPOSE: The purpose of the current study was to determine if there is a relationship between an increased hindfoot moment arm and a pes planovalgus deformity or a difference in hindfoot moment arm between pes planovalgus deformity and a control population. MATERIALS AND METHODS: IRB approval was obtained. A retrospective chart review of 86 patients was performed from the senior author’s clinical practice. Forty-three controls (no history of significant foot or ankle pain) as well as 43 patients with a clinical diagnosis of pes planovalgus deformity with complete foot, ankle and hindfoot alignment radiographs of the affected were included. On the lateral radiographs, the talar-first metatarsal angle, calcaneal pitch, talocalcaneal angle, medial column height, calcaneal-fifth metatarsal height, and lateral column height was measured. The hindfoot moment arm was calculated on hindfoot alignment radiograph. On the AP radiographs, talar-first metatarsal angle and talar head uncoverage was measured. RESULTS: Forty-three patient with pes planovalgus deformity and forty-three normal patients were identified. There was a statistically significant difference between the pes planovalgus and control groups with respect to the talar-first metatarsal angle, calcaneal pitch, talocalcaneal angle, medial column height, calcaneal-fifth metatarsal angle, and hindfoot moment arm (p <0.001, <0.001, 0.012, <0.001, <0.001, <0.001 respectively). The medial column height was correlated most strongly to the hindfoot moment arm (R squared – 0.48). CONCLUSIONS: This study showed a statistically significant difference between patients with pes planovalgus group and a normal patient population with respect to the talar-first metatarsal angle, calcaneal pitch, talocalcaneal angle, medial column height, calcaneal-fifth metatarsal angle, and hindfoot moment arm. The clinical significance of this study is that in the setting of a pes planovalgus deformity, the clinician should consider obtaining a bilateral hindfoot alignment view in order to quantify the hindfoot deformity and ensure that the planned surgical procedure can correct the deformity.