Pes Cavus - Not just a clinical sign. Diagnosis, Aetiology and Management

Abstract

Definition Pes cavus is an umbrella term describing a spectrum of foot shapes with a high arch. Pure Pes cavus occurs when the metatarsal bones are plantarflexed relative to the hindfoot – described as ‘forefoot plantaris’ – which increases the height and curvature of the medial longitudinal arch (Figure 1). When the patient weight-bears, the hindfoot is pushed into dorsiflexion by the plantarflexed forefoot (Figure 2). A high arch accompanied by a medially angulated heel is termed pes cavovarus (Figure 3). When this is complicated by foot drop and equinus of the ankle, it is described as pes equinocavovarus. Another variant, pes calcaneovarus, occurs when the primary deformity is excessive ankle and hindfoot dorsiflexion; in order to place the foot flat on the ground, the forefoot plantarflexes, leading to a high arch. On radiographs, a high arch manifests as a Meary’s angle of over 5 degrees – the angle between the long axis of the talus and the first metatarsal in the lateral view (Figure XR 4). The talus and the calcaneum are dorsiflexed, with calcaneal pitch exceeding 30 degrees. The calcaneum appears shortened when in varus. On the dorso-plantar view, supination is seen as a narrow talo-calcaneal angle (Figure XR 5). The wide spectrum of normality leads to controversy over the inclusion of milder variants in the definition of pes cavus. An objective measure of the degree of supination or pronation, the Foot Posture Index (FPI), has been developed and validated. However, while the FPI describes and quantifies foot shape, it does not delineate the normal foot from pes cavus. In practice, what is important is that subtle cases of pes cavus are identified and that potential pathology is considered.