Position, size and orientation of the peroneus longus tubercle in patients with cavovarus feet

Plantarflexion of the first ray is an important component of cavovarus foot deformities, which is thought to be due to the pull of the peroneus longus muscle. We inferred its action by studying its insertion into the peroneus longus tubercle (PLT). Our aim was to determine how PLT orientation and morphology differs in cavovarus feet compared to controls on weightbearing computed tomography (WBCT) imaging.

We retrospectively analysed 30 WBCT scans from patients with cavovarus feet and Charcot-Marie Tooth disease. We compared these to 30 normal feet using previously described measurements of PLT morphology: tubercle-to-floor (T-F) distance; bisecting angle and tubercle-to-metatarsal (T-MT) angle. The intraclass correlation coefficient (ICC) was used to assess reliability.

Individuals with cavovarus feet were found to have a higher T-F distance by an average of 9.63 mm (p < 0.001), a greater vertical bisecting angle (> 10 °, p = 0.002) and a lower T-MT angle (<11 °, p < 0.001). This suggests net forefoot supination with relative pronation of the first ray. Intra- and Inter-observer reliability was excellent.

We observed the PLT is both greater in size and more vertically oriented in cavovarus feet, with relative pronation of the PLT orientation when compared to the rest of the forefoot. The height of the PLT from the floor is also greater. Overall, this likely infers that the action of peroneus longus in cavovarus feet is to plantarflex and pronate the first ray, relative to a supinated forefoot.

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