BACKGROUND:The 3-dimensional nature of adult acquired flatfoot deformity can be challenging to characterize using radiographs. We tested the hypothesis that measurements on weight-bearing (WB) ...cone-beam computed tomography (CT) images were more useful for demonstrating the severity of the deformity than non-weight-bearing (NWB) measurements.
METHODS:We prospectively enrolled 12 men and 8 women (mean age, 52 years; range, 20 to 88 years) with flexible adult acquired flatfoot deformity. The subjects underwent cone-beam CT while standing (WB) and seated (NWB), and images were assessed in the sagittal, coronal, and axial planes by 3 independent observers who performed multiple measurements. Intraobserver and interobserver reliabilities were assessed with the Pearson or Spearman correlation and the intraclass correlation coefficient (ICC), respectively. Measurements were compared using paired Student t tests or Wilcoxon rank-sum tests. P < 0.05 was considered significant.
RESULTS:We found that overall the measurements had substantial intraobserver and interobserver reliability on both the NWB images (mean ICC, 0.80; range, 0.49 to 0.99) and the WB images (mean ICC, 0.81; range, 0.39 to 0.99). Eighteen of 19 measurements differed between WB and NWB cone-beam CT images, with more pronounced deformities on the WB images. The most reliable measurements, based on intraobserver and interobserver reliabilities and the difference between WB and NWB images, were the medial cuneiform-to-floor distance, which averaged 29 mm (95% confidence interval CI = 28 to 31 mm) on the NWB images and 18 mm (95% CI = 17 to 19 mm) on the WB images, and the forefoot arch angle (mean, 13° 95% CI = 12° to 15° and 3.0° 95% CI = 1.4° to 4.6°, respectively) in the coronal view and the cuboid-to-floor distance (mean, 22 mm 95% CI = 21 to 23 mm and 17 mm 95% CI = 16 to 18 mm, respectively) and the navicular-to-floor distance (mean, 38 mm 95% CI = 36 to 40 mm and 23 mm 95% CI = 22 to 25 mm, respectively) in the sagittal view.
CONCLUSIONS:Measurements analogous to traditional radiographic parameters of adult acquired flatfoot deformity are obtainable using high-resolution cone-beam CT. Compared with NWB images, WB images better demonstrated the severity of osseous derangement in patients with flexible adult acquired flatfoot deformity.
LEVEL OF EVIDENCE:Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.
•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.
