Current Concepts In Orthotic Therapy For Pes Cavus
Despite the prevalence of pes cavus, questions abound about etiology, classifications and appropriate treatment. Accordingly, these authors sort through the various classification systems, offer insights on the pathomechanics and share their thoughts on the role of orthoses for managing symptoms of pes cavus.
Pes cavus occurs in about 8 to 15 percent of the population but it does not get nearly as much attention in the medical literature as its counterpart pes planus.1 Sixty percent of the population with cavus feet develop foot pain.2
Why does this chronically painful condition with such a large prevalence remain somewhat of an unsolved mystery in terms of its etiology and development? Although medical knowledge regarding pes cavus exists, the research and treatment options, as well as any theory or hypothesis as to why humans develop this deformity, are quite limited. Traditionally, we have considered pes cavus a neuromuscular problem with a surgical answer. By combining what is known with what we can hypothesize,perhaps we can establish a new and more successful approach to pes cavus.
Pes cavus has a variety of classifications. However, many of these overlap and lead to confusion. The most common classification system categorizes pes cavus as neuromuscular, congenital or traumatic. (See “A Guide To The Classification Of Pes Cavus Etiology”) Researchers often separate an idiopathic category from congenital when they classify pes cavus.3 A large retrospective survey reviewed 465 patients with pes cavus and found that 81 percent were classified as having idiopathic pes cavus and 19 percent had neuromuscular pes cavus.4 Another study reviewed 77 patients in a pes cavus clinic and found that 33.8 percent were idiopathic and 66.2 percent were neuromuscular.4 Despite this discrepancy, a significant portion of the pes cavus patients in these studies had no known etiologic source of deformity (idiopathic classification).
The identification of the high arched foot has also been classified by way of footprint morphology, radiography, visual inspection and, most recently, by a foot posture index.2,5-7 The foot posture index (FPI) system is the most comprehensive method since it distinguishes all foot types (not just the cavus foot) by point criteria. This validated and consistent observation identifies the cavus foot as any foot that has a FPI score of -2 to -12 on a scale of -12 to +12. A normal foot has a score of -5 to +5.
The structure of pes cavus falls into anterior, posterior and global categories. The anterior cavus is either total (indicating plantarflexion of the entire forefoot) or local (plantarflexion of the first ray only). The posterior type has a high calcaneal inclination angle but no forefoot equinus. The global type is a combination of both deformities.
The pes cavus foot has also been classified by variations of function, either flexible or rigid. Although this classification is often the least emphasized, function may prove to be the most important consideration when considering orthotic therapy. These two variations of functioning cavus feet, though similar in appearance, act very differently. Anecdotally, there is an assumption that pes cavus deformity begins as a flexible entity and will become rigid if it is not treated. However, no evidence supports this speculation.
Understanding The Pathomechanics Of Pes Cavus
The classification of pes cavus with so many different parameters may signal that the true etiology of pes cavus may have escaped the medical community. The tradition of classifying pes cavus does not help the situation and circumvents the investigation into the possible true cause which probably lies in imbalance in muscle forces and strength.