The Association Between a Hindfoot Deformity Assessed by Weightbearing CT and the Full Leg Alignment

CATEGORY: Hindfoot INTRODUCTION/PURPOSE: The exact relationship between different types of hindfoot deformities and the full leg alignment is currently unclear. Therefore, our aim is to assess hindfoot alignment on a weight-bearing CT (WBCT) and its association with the full leg radiographic alignment. METHODS: A retrospective analysis was performed on a study population of 109 patients (mean age of 53 years ± 14.49) with a varus or valgus hindfoot deformity and the presence or absence of ankle osteoarthritis (OA) based on the Takakura classification. The mechanical hindfoot - (mHA) and subtalar vertical angle (SVA) were determined on WBCT, while the mechanical tiba – (mTA) and mechanical tibiofemoral angle (mTFA) were measured on full leg radiographs. RESULTS: In patients with ankle OA, a hindfoot valgus deformity was associated with a significantly higher mean varus alignment of the knee (mTFA = -1.8°±2.1; mTAx= -4.3°±1.9) compared to a valgus alignment of the knee (mTFA = 0.3°±2.6; mTAx= -1.4°±2.2; P <0.001) in patients with a varus hindfoot (Fig1A, B). The opposite relation was found in patients without ankle OA (P <0.001). The SVA was significantly more orientated in valgus (mean=106.9°±8.0) for patients with a hindfoot valgus compared to a higher varus orientation (mean=89.3°±13.9) in patients with a hindfoot varus deformity (P <0.001). The same pattern was found in patients without ankle OA, but not significant (P >0.05). CONCLUSION: A valgus hindfoot deformity demonstrated a higher varus alignment of the knee when compared to patients with a hindfoot varus deformity, if ankle OA was present. The subtalar joint did not attain an overall compensatory correction towards the hindfoot deformity as opposed to a compensatory orientation of the tibia alignment. In clinical practice, these findings could improve the current understanding of both joint preserving as well as joint replacing procedures of the hindfoot and the knee.