Prescription Advice for Treating the Cavus Foot
The cavus foot can be a challenge for podiatrists. Through the work of Professor Josh Burns and colleagues, we’re gaining a better understanding of the prevalence of foot pain and the impact this has on people with a cavus foot. We know that in people with a cavus foot common presenting complaints include metatarsal head pain, lateral ankle instability and peroneal tendinopathy. Therefore the goals of treating the cavus foot should include (but are not limited to):
- Controlling/reducing forefoot forces
- Increase the plantar surface contact area
- Control frontal plane supinatory forces, especially at the subtalar joint
- Pronate the midtarsal joint
The cavus foot should raise the clinical suspicion of underlying neuromuscular disease including Charcot-Marie-Tooth disease (hereditary sensory and motor neuropathy), muscular dystrophy, post-polio and cerebral palsy just to name a few. Of course patients may develop a cavus foot as a result of trauma, or it may be an idiopathic cavus foot.
As with all lower limb conditions that require orthotic therapy, the key is to start with a good cast or scan. Whether you’re using plaster or you’re scanning, it’s important to capture the complex curves of the cavus foot. This requires much more attention to detail in a patient with a cavus foot. Whilst capturing subtalar neutral position is important here, it’s absolutely critical that the midtarsal joint is fully pronated to capture what is typically a large forefoot valgus. By capturing the anatomical forefoot valgus of the patient, it makes the orthotic more effective at pronating the midtarsal joint and resisting subtalar joint supination.
Whilst most of the orthotics we do for cavus feet are poured vertical (or aligned vertically in our CAD program), doing an everted pour certainly has its place. It will increase the lateral arch contours, but you must also keep in mind it will decrease the medial arch height. Plantar fascial accommodations are typically used (usually 3-5mm) and lateral heel skives or cuboid notches can also be used to resist subtalar joint supination.
In terms of shell material, we typically advise to go for a more flexible shell material for the cavus foot. 2-3mm polyprolylene/subortholen/PA11 are commonly used materials. These are often reinforced laterally. For hand crafted devices we can reinforce the lateral side of the device with EVA. With PA11 (EnviroPoly) we can modify the design to have it printed thicker down the lateral side so it may be 2mm on the medial side and 3.5mm on the lateral side. We can also extend the extrinsic rearfoot post laterally to further reinforce the lateral side of the shell. Extrinsic forefoot valgus posting is another common addition to gain further lateral control. Heel lifts can be utilized in cases with equinus.
Whilst treating the cavus foot can be challenging, by understanding the goals of treatment, the casting/scanning requirements and the shell and post options, podiatrists should be able to gain good control to reduce pathological loads.
