Hindfoot alignment of adult acquired flatfoot deformity: A comparison of clinical assessment and weightbearing cone beam CT examinations

•Valgus hindfoot alignment in patients with AAFD is significantly influenced by the anatomical landmarks used to define the angular measurement.•Clinical assessment of hindfoot valgus by an experienced observer was significantly different from the HAA measured in WB CBCT images.•Clinical evaluation underestimated the hindfoot valgus as measured by the HAA. Clinical assessment of hindfoot alignment (HA) in adult acquired flatfoot deformity (AAFD) can be challenging and weightbearing (WB) cone beam CT (CBCT) may potentially better demonstrate this three-dimensional (3D) deformity. Therefore, we compared clinical and WB CBCT assessment of HA in patients with AAFD. In this prospective study, we included 12 men and 8 women (mean age: 52.2, range: 20–88) with flexible AAFD. All subjects also underwent WB CBCT and clinical assessment of hindfoot alignment. Three fellowship-trained foot and ankle surgeons performed six hindfoot alignment measurements on the CT images. Intra- and Inter-observer reliabilities were calculated using intra-class correlation (ICC). Measurements were compared by paired T-tests, and p-values of less than 0.05 were considered significant. The mean of clinically measured hindfoot valgus was 15.2 (95% confidence interval [CI]: 11.5–18.8) degrees. It was significantly different from the mean values of all WB CBCT measurements: Clinical Hindfoot Alignment Angle, 9.9 (CI: 8.9–11.1) degrees; Achilles tendon/Calcaneal Tuberosity Angle, 3.2 (CI: 1.3–5.0) degrees; Tibial axis/Calcaneal Tuberosity Angle, 6.1 (CI: 4.3–7.8) degrees; Tibial axis/Subtalar Joint Angle 7.0 (CI: 5.3–8.8) degrees, and Hindfoot Alignment Angle 22.8 (CI: 20.4–25.3) degrees. We found overall substantial to almost perfect intra- (ICC range: 0.87–0.97) and inter-observer agreements (ICC range: 0.51–0.88) for all WB CBCT measurements. Using 3D WB CBCT can help characterize the valgus hindfoot alignment in patients with AAFD. We found the different CT measurements to be reliable and repeatable, and to significantly differ from the clinical evaluation of hindfoot valgus alignment. Level of evidence: Level II—prospective comparative study.