Assessment of Bony Subfibular Impingement in Flatfoot Patients Using Weight-Bearing CT Scans

BACKGROUND:: Lateral hindfoot pain in patients with flatfoot deformity is frequently attributed to subfibular impingement. It remains unclear whether this is primarily due to bony or soft-tissue impingement. No studies have used weight-bearing CT scans to evaluate subfibular impingement. METHODS:: Patients with posterior tibial tendonitis were retrospectively searched and reviewed. Subjects had documented flatfoot deformity, posterior tibial tenderness, weight-bearing plain radiographs, and a weight-bearing CT scan. CT scans were evaluated for calcaneofibular impingement on the coronal view and talocalcaneal impingement on the sagittal view. The distance between these structures was measured, along with the sinus tarsi volume. In the second part of this study, 6 normal volunteers underwent weight-bearing CT scans on a platform that held both feet in 20 degrees of varus, followed by 20 degrees of valgus. The same measurements were performed. RESULTS:: Thirty-five percent of flatfoot patients with posterior tibial tendonitis had bony impingement between the fibula and calcaneus on the coronal view. Thirty-eight percent had bony impingement between the talus and calcaneus on the sagittal view. Subjects with bony impingement based on CT scan had significantly higher talonavicular abduction angles on plain radiographs than those without impingement. Sinus tarsi volume decreased by more than half when the subtalar joint moved from varus to valgus in normal controls. CONCLUSION:: Bony subfibular impingement in patients with flatfeet was less common than previously reported. Accurate diagnosis of bony impingement may be useful for surgical decision-making. LEVEL OF EVIDENCE:: Level III, retrospective comparative study.