WEIGHT-BEARING COMPUTER TOMOGRAPHY (CT) SCAN OF THE FEET IN PES PLANUS

Abstract

CT scans of thirty pes planus and eighteen normal feet were obtained in a simulated weight-bearing mode at 50% of body weight. The navicular skin distance was 22% less (1.9vs2.5cm) in the pes planus feet and forefoot supination was only 50% of normal (8.9vs18.6 degrees). Subtalar subluxation was observed in only the most severe pes planus feet. Navicular skin distance relates to medial arch collapse; loss of forefoot supination reflects the rigidity of the forefoot compensation to hindfoot valgus. Severe pes planus results in subtalar subluxation. The radiological indices described have not previously been reported in the literature.

To compare the inter-tarsal relationships of the pes planus foot to the normal foot in the weight-bearing state.

Weight-bearing CT scan of the feet is a practical examination with rapid set-up and minimal patient discomfort. Preliminary results demonstrate differences in the inter-tarsal relationships of pes planus feet compared to normal feet. Better understanding of pes planus deformity will advance clinical evaluation and treatment strategies.

Radiological indices described have not previously been reported in the literature.

Thirty pes planus and eighteen normal feet were imaged. All patients were able to tolerate the six- minute exam at 50% of body weight. Total study time averaged fifteen minutes. The navicular skin distance was 22% less (1.9vs2.5 cm) in pes planus feet compared to normal feet. Pes planus feet had only 50% of the normal forefoot supination (8.9vs18.6 degrees). Lastly, subtalar joint subluxation was observed in only the most severe pes planus feet. Values ranged from 0.2 to 1.1cm.

Axial CT images of 1mm thickness with 0.5mm overlap were obtained at a weight-bearing load of 50% of body weight using the weight-bearing CT device. Coronal and Sagital images were then reconstructed.

Radiological indices obtained can be related to the clinical picture of the pes planus foot. The navicular skin distance reflects medial arch collapse, where as the lack of forefoot supination reflects the rigidity of the forefoot compensation to hindfoot valgus. Severe hindfoot valgus in pes planus results in subtalar sub-luxation.