ACNRJF13_Layout 1 13/01/2013 22:33 Page 16 REHABILITATION ARTICLE Pes Cavus – Not Just a Clinical Sign Diagnosis, Aetiology and Management Mr Thomas Ball, he term Pes cavus describes the deformity of Figure 1 MRCS, MRCP, MA(Cantab) is a Specialty Registrar in Trauma a high arched, relatively stiff foot. It has a and Orthopaedics in the South T variety of neurological and other causes. West Peninsula, currently working Management depends on the aetiology, rapidity of at Royal Cornwall Hospital. He progression and the severity of symptoms. aims to specialise in foot and ankle surgery and correction of lower limb deformity. Definition Pes cavus is an umbrella term describing a spec- trum of foot shapes with a high arch.1 Pure Pes cavus occurs when the metatarsal bones are plan- tarflexed 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 plan- tarflexed forefoot (Figure 2). Mr Michael Butler, A high arch accompanied by a medially angu- MA MB BS FRCS (TR&Orth) lated heel is termed pes cavovarus (Figure 3). is a Consultant Orthopaedic Surgeon and Foot and Ankle When this is complicated by foot drop and Specialist at the Royal Cornwall equinus of the ankle, it is described as pes Hospital in Truro and is a regular equinocavovarus. A n o t h e r va r i a n t , pes calcaneo- officer in the Army. Mr Butler varus, occurs when the primary deformity is treats patients for complex excessive ankle and hindfoot dorsiflexion; in problems of the foot and ankle Box 1: Causes of Pes cavus and is a Review Board Member for order to place the foot flat on the ground, the fore- Foot and Ankle Surgery. foot plantarflexes, leading to a high arch. Progressive neurological disorders On radiographs, a high arch manifests as a • Hereditary Sensorimotor Neuropathies (HSMN) Meary’s angle of over 5 degrees – the angle or Charcot-Marie-Tooth disease (CMT) (78%)3 between the long axis of the talus and the first • Hereditary sensory and autonomic neuropathies metatarsal in the lateral view (Figure XR 4). The talus and the calcaneum are dorsiflexed, with • Friedreich ataxia calcaneal pitch exceeding 30 degrees.1 The calca- • Spinal or brain Tumour neum appears shortened when in varus. On the • Spinal muscular atrophy dorso-plantar view, supination is seen as a narrow • Spinal trauma Stephen Parsons, talo-calcaneal angle (Figure XR 5). • Syringomyelia The wide spectrum of normality leads to MA BS FRCS FRCS(Ed) • Myelodysplasia controversy over the inclusion of milder variants has been a Consultant • Spinal dysraphism: spina bifida, spina bifida Orthopaedic and Trauma Surgeon in the definition of pes cavus. A n o b j e c t ive occulta, diastematomyelia4 at the Royal Cornwall Hospital measure of the degree of supination or pronation, since 1991. He is a past President of • Muscular dystrophy the British Orthopaedic Foot and the Foot Posture Index (FPI), has been developed 2 Static neurological disorders Ankle Society and was the and validated. However, while the FPI describes inaugural Chairman of the and quantifies foot shape, it does not delineate the • Cerebral palsy Education Committee. He has also normal foot from pes cavus. served on the Council of the • Stroke In practice, what is important is that subtle European Foot and Ankle Society • Poliomyelitis for 4 years. His research and cases of pes cavus are identified and that poten- • Spinal nerve root injury development interests cover new tial pathology is considered. procedures in the forefoot, • Peroneal nerve injury4 arthroscopic surgery in the ankle, hindfoot and midfoot and Aetiology, classification and pathophysiology Other causes A list of causes is given in box 1. These conditions assessment at surgery for the • Scarring of the deep posterior compartment painful flat foot. He has been have differing pathophysiology, but unbalanced after compartment syndrome5 invited to lecture nationally and muscular forces are almost always at the root of internationally at scientific • Foot trauma cavus feet. congresses and instructional • Tarsal coalition courses. The sole of the foot can be conceived as a tripod, consisting of the first metatarsal head, fifth • Under-corrected congenital talipes equinovarus Correspondence to: metatarsal head and heel. All three points should • Iatrogenic (e.g. overzealous surgery for pes Email: [email protected] be in contact with the ground during stance, with planus) the ankle balanced over the triangular base that • Idiopathic / familial they form. 16 > ACNR > VOLUME 12 NUMBER 6 > JANUARY/FEBRUARY 2013 ACNRJF13_Layout 1 13/01/2013 22:33 Page 17 REHABILITATION ARTICLE Figure 2 Figure 3 Figure XR 4 Figure XR 5 In typical cases of pes cavovarus associated with HSMN,3 tibialis poste- rior and peroneus longus are consistently stronger than tibialis anterior (TA) and peroneus brevis,6 resulting in plantarflexion of the first ray and adduction of the forefoot.4,7 This creates pronation of the forefoot relative to the hindfoot.8 The plantar fascia contracts, further depressing the first metatarsal head. To keep the tripod flat on the ground, the hindfoot dorsi- flexes and supinates into varus. Hindfoot varus may be flexible at first but becomes progressively fixed.1,8 Once the heel’s point of contact is medial to the centre of the ankle, there is a moment that tends to exacerbate the hindfoot varus. The equinus ensues. Achilles tendon’s insertion is medialised and it becomes a secondary The calcaneovarus variant is seen in poliomyelitis, low spinal inverter.1 Thus pes cavovarus may start as a forefoot-driven phenomenon dysraphism or after overzealous surgical lengthening of the Achilles and later become hindfoot-driven. tendon. Paralysis of the calf muscles leads to excessive ankle dorsiflexion Frequent toe deformities are partly caused by weak intrinsic foot and compensatory forefoot plantaris. muscles. They are overcome by the extrinsic muscles: extensor digitorum In children, the skeleton reacts to the forces upon it, with differential longus (EDL), flexor digitorum longus (FDL), extensor hallucis longus growth at the physis, according to Wolff’s law. The muscle imbalances (EHL) and flexor hallucis longus (FHL). The imbalance leads to hyperex- cause deformities that initially occurred through the joints to become tension of the metatarso-phalangeal joints (MTPJs) and flexion of the fixed in the bony architecture of the mature foot. interphalangeal joints, or ‘clawing’. This is made worse when EHL and EDL are recruited to aid a weak TA in dorsiflexing the foot.4 The plantar Epidemiology and Genetics fascia, attached to the proximal phalanges, tightens when they hyperex- Some authors quote the prevalence of high-arched feet as 8-15% in the tend. This exaggerates the medial longitudinal arch via the windlass population;11,12 but the true prevalence of pes cavus associated with mechanism.1 Eventually the slips of plantar fascia toes become dorsal to pathology is much lower. About 37 in 100,000 people are affected by the centre of the MTPJ, thus becoming a perverse extensor. A theory that CMT.7 A recent review has summarised our knowledge of the varied weak intrinsic muscles account for all the deformities of pes cavus9 phenotypes and their genetic basis.13 In the UK, 90% of patients have cannot, however, be sustained.10,6 autosomal CMT type 1 (demyelinating) or type 2 (axonal). Most muta- The Equino-cavovarus deformity is seen as the end stage of HSMN- tions involve the peripheral myelin protein 22 gene on chromosome 17. induced pes cavus. Once there is no active dorsiflexion, the ankle plan- Genetic testing has progressed such that 70% of patients can be given a tarflexes, the calf muscles and posterior joint capsule contract, and genetic diagnosis. Our ability to relate the different forms of these genes ACNR > VOLUME 12 NUMBER 6 > JANUARY/FEBRUARY 2013 > 17 ACNRJF13_Layout 1 13/01/2013 22:33 Page 18 REHABILITATION ARTICLE to their variable phenotypic expression is still Box 2: Symptoms of pes cavus disorder such as spinal dysraphism or a space limited, although mRNA levels of some lipid occupying lesion must be excluded by metabolism genes in skin biopsies may offer a • Metatarsal overload magnetic resonance imaging of the brain and way to predict phenotypic expression.13 CMT • Heel pain spinal cord. type 2 seems to produce milder symptoms • Lateral overload 7 with a slower progression than type 1. • Stiffness Treatment • Ankle sprains Symptoms and signs, and their relation- Non-surgical treatments • Ill-fitting footwear, toes rubbing ship to biomechanics Non-surgical treatment is instituted early and The foot serves as an organ of load distribu- • Ulceration is chiefly delivered by podiatrists and ortho- tion, shock absorption, balance and propul- tists, preferably working alongside doctors in a sion. Pes cavus interferes with all of these func- foot and ankle clinic. Orthotic treatment can tions.1 sensory changes, weakness and clumsiness broadly be separated into four types: pressure Supination of the hindfoot normally results should be sought. Back pain or headaches relief, correction of deformity, accommoda- in a change of the foot from a loosely packed, may signify a central cause. Family history may tion of deformity, and splinting. Chiropodists flexible, energy absorbing structure to a tightly suggest a hereditary cause. and podiatrists can provide simple devices, packed, stiffer lever. This change occurs natu- General examination may reveal features of but more involved orthoses are made by an rally during the gait cycle. When the hindfoot neurological conditions such as “champagne orthotist. remains supinated throughout the gait cycle, bottle legs” (Charcot-Marie-Tooth disease), A simple cushioning orthosis alone may however, the reduced flexibility lessens the scoliosis in Friedreich ataxia, or a naevus, help symptoms from pressure overload.12 foot’s capability as a shock absorber1 and dimple or patch of hair over the spine in spina Pressure on the metatarsal heads is alleviated diminishes its ability to balance on uneven bifida occulta.