Background: Patients with symptomatic flatfoot deformity often present with pain in the lateral part of the hindfoot. The cause of this pain has not been clearly established. Impingement between the talus and the calcaneus or between the calcaneus and the fibula has been suggested as a cause but has not been documented.
Methods: We examined the computed tomographic scans, performed with simulated weight-bearing, of nineteen adult patients with symptomatic flatfoot to determine the potential causes of pain in the lateral aspect of the foot. The scans were performed with use of a custom loading frame designed to simulate weight-bearing with the foot in a neutral position while a 75-N axial compressive load was applied. Four examiners independently examined the coronal images as well as sagittal plane reconstructions for direct (bone-on-bone contact) and indirect (subchondral sclerosis or cysts) evidence of (1) extra-articular contact between the talus and the calcaneus in the sinus tarsi and (2) contact between the calcaneus and the fibula. The data were compared with those from five scans of normal feet in neutral alignment.
Results: Overall, the prevalence of sinus tarsi impingement was 92% and the prevalence of calcaneofibular impingement was 66% in the flatfoot group versus 0% and 5%, respectively, in the control group. The study patients who had calcaneofibular impingement also had sinus tarsi impingement. There was substantial agreement among the examiners as to whether impingement was present.
Conclusions: There appear to be two frequently occurring extra-articular sources of bone impingement in the lateral aspect of the hindfoot in adults with symptomatic severe flatfoot deformity. The impingement in the lateral aspect of the hindfoot may first occur within the sinus tarsi and then involve the calcaneofibular region. Cyst formation and/or sclerosis in this region that is visible on plain radiographs or on computed tomographic scans performed without weight-bearing should create suspicion of impingement.