Foot and Ankle
ANATOMY
Greek πºvζ (root πºδ-) is Latin pes (root ped-): “foot”, which gives the root -ped- in English. Do not confuse Greek παιζ (root παιδ-): “child”, which is represented in American usage as -ped- after the custom of simplifying diphthongs, as in Pediatrics. The only exception in American usage is the term Orthopædic, which retains the diphthong to avoid limitation of scope to the foot.
The foot may be divided into hindfoot, midfoot, and forefoot [A]. The hindfoot consists of the talus and calcaneus. Latin talus is Greek αστραγαλºζ: astragalus. The midfoot is made up of cuboid bone, navicular bone, and the three cuneiform bones (medial, intermediate, and lateral, or numbered). Latin navicula is Greek σκαφη: “small boat, skiff,” to describe the bone’s shape; hence the distinction “tarsal navicular or scaphoid.” The forefoot includes metatarsal bones and phalanges. Hindfoot and midfoot correspond to the galenic concept of ταρσºσ: “tarsus,” as the equivalent in the foot of καρπºσ: “carpus” in the hand. The mid-or transverse tarsal joint, through which the French surgeon François Chopart (1743-1795) recommended amputation, consists of talonavicular and calcaneocuboid articulations. The French surgeon Jacques Lisfranc de St. Martin (1790-1847) favored amputation at the junction of tarsus and metatarsus, from Greek µετα-: “next”.
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 B Accessoria of the foot T: os trigonum (15%). N: naviculare accessorium (15%). C: calcaneus secundarius (5%). I: os intermetatarseum (5%). V: os vesalianum (rare). |
Distinguish normal motion from morbid deformity [A]. This resembles the distinction of version (normal “turning” of a part of a long bone) from torsion (abnormal or “excessive”) for long bones of the lower limb. When ankle plantar flexion exceeds the normal range or is fixed (eliminating dorsiflexion) due to disease, this is known as equinus, from Latin equus: “horse,” after the posture of a horse’s foot. The opposite is known as calcaneus, after the bone that is most distinctive in the deformity. The midfoot and forefoot do not move actively but may be deformed. Adductus describes “direction toward” and abductus “direction away” from the midaxis of the foot. Cavus describes a medial plantar longitudinal arch that is “scooped out” higher than normal, whereas in planus, the arch is “flat.” In pronation, the forefoot appears rotated toward the midline due to flexion or depression of the first ray; elevation or extension of the first ray rotates the forefoot away from the midline into supination. Toe deformities are distinguished according to the joint affected. Flexion of the distal interphalangeal joint likens the toe to a diminutive mallet on account of a smaller distal skeletal element than is presented with flexion of the intermediate interphalangeal joint, which is likened to a hammer. Interphalangeal flexion with metatarsophalangeal extension gives the toe a claw appearance.
Anatomists and surgeons differ at the ankle. The former group’s flexion, following the convention that applies this term to reduction of angle in the direction of motion at a joint, is the latter’s dorsiflexion. The opposite motion is termed extension by the anatomist and plantar flexion by the surgeon.
Anatomists and surgeons also differ at the foot (and the hand). Normal motion is described relative to the foot, whereas the midaxis of the body is used to define deformity. Valgus refers to pointing of the hallux (the distal skeletal element) “away” from the body midaxis at the metatarsophalangeal joint. The equivalent active motion is under the action of adductor hallucis muscle, which pulls the great toe away from the midaxis of the body but “toward” the midline of the foot.
The foot may be divided into columns. Medial includes the talus and first ray. Lateral includes the calcaneus and fifth ray. This concept is fundamental to an understanding of foot mechanics (q.v.).
The foot is replete with accessory ossicles [B]. Some have fanciful names, such as os vesalianum at the base of the 5th metatarsal bone, after the Barbantian “Father of Anatomy” Andreas Vesalius (1514-1564). Others may be sufficiently common and sufficiently noisome to be worthy of a classification (cf. Accessory Navicular Bone). The malleoli may present separate ossification centers, of which appearance peaks between 6 and 9 years and which fuse with remainder of bone 1 to 2 years later. Distinguish these normal variants from avulsion fracture or other disease.
MECHANICS
Two models aid understanding of normal function and disease of the foot.
Tripod
This highlights the interconnectedness of the foot in bearing weight [C]. The legs of the tripod are the first and fifth rays, as well as the calcaneus. In a supinated forefoot with a hypermobile first ray, the calcaneus tips into valgus at the subtalar joint as the medial longitudinal arch reduces to produce a flatfoot. Correction of a flatfoot by calcaneal lengthening without correction of forefoot supination will fail as the first ray returns to the ground by hindfoot eversion
Acetabulum Pedis
Calcaneus and navicular bone (with remainder of foot) form a cup that rotates around a ball formed by the head of the talus [D]. In clubfoot, the acetabulum is displaced plantad and medialward, such that navicular bone abuts tibial malleolus and the head of the talus becomes palpable at lateral proximal dorsum of the foot. The acetabulum moves in an opposite direction in flatfoot. This concept underpins casting for clubfoot, which is rotated out of adductus and varus via the acetabulum. In flatfoot, cutting the calcaneus and lengthening the lateral column swings the foot around the head of the talus to reduce hindfoot valgus and restore normal alignment of the first ray with the talus.
EVALUATION
History
The foot has been a source of complaint and concern in every culture and in every age. A dichotomy may exist between child and parent, and between parent and physician. A parent may regard flexible flatfoot as an abnormality worthy of treatment when the child has no concerns and to the surgeon it is a normal variant. The foot may be the focus of a remote condition, either benign such as in-toeing due to tibial torsion or grave such as cavus as a sign of neural disease.
Physical Examination
Global Perform a complete assessment. The foot may manifest a sign of primary neural disease, such as dysrrhaphism, or hereditary motor and sensory neuropathy. Ask the patient to walk and run. Which way do the feet point? Do they appear symmetric, or does asymmetry betray a problem remote from the feet such as at the hip? Is there a normal progression of heel-flat-toe in stance and ankle flexion in swing?
Focal The foot is a dynamic structure [E]. Start viewing the foot from the back. What is the position of the hindfoot standing and when the patient is up on the metatarsal heads? Add a block to support the lateral border of the foot: does the hindfoot evert as the medial front leg of the tripod sinks to the floor? These are tests of flexibility of the subtalar joint. Are “too many toes” visible beyond either malleolus in the standing position? How much space is there under the medial longitudinal arch in the lateral position? Evaluate the foot in weight-bearing and unloaded positions. Does the arch shape vary between the two?
Evaluate the skin, which tells a story. Callus is a response to abnormal pressure, which provides a functional outcome of deformity. Ulcer may have an exogenous cause, such as constrictive shoe wear, or endogenous cause, such as sensory loss. A single deep furrow is a sign of reduced skin motion over a joint with fixed deformity, such as posterior to an equinus ankle in structural clubfoot. A primary physician may rely on the observation that multiple fine creases suggest stretching and relaxation of skin over a mobile ankle to distinguish metatarsus adductus, a benign condition, from clubfoot.
Pain varies according to age [F]. Most disorders and complaints concentrate around the turn of the decade. Palpate for tenderness: the foot is geographic and will reveal the source of pain [G].
 C The foot as tripod Thumb represents calcaneus. As a neutral calcaneus (green) rotates into valgus (brown), the medial longitudinal arch diminishes (orange) to keep ground contact with the first ray, which is relatively extended bringing the forefoot into supination. By contrast, when the calcaneus assumes a varus inclination (red), the arch elevates (blue) and the forefoot pronates as the first ray flexes to maintain contact with the ground. |
 D Acetabulum pedis Calcaneus (C) and navicular bone (N), with intervening ligaments (pink), may rotate around talus (T) plantad and medialward (red), for example, in clubfoot, or lateralward and dorsad (green), for example, in flatfoot. |
 E Dynamic examination of the foot In standing, weight-bearing position, the foot is flat (white). Upon standing on the metatarsal heads, the hindfoot inverts (red) and the medial longitudinal arch reconstitutes (blue), demonstrating that the deformity is flexible. |
 F Foot pain Foot pain varies according to age. |
 G Foot pain Foot pain is geographic. A: arthritis. B: bunion. b: bunionette. C: coalition. E: enthesitis. F: Freiberg infraction. I: osteomyelitis. K: Köhler condition. N: accessory navicular. O: osteochondritis dissecans. P: paronychia. S: Sever apophysitis. T: trauma. Tr: os trigonum. |
 H Radiographic examination of the foot Measure relationships in anteroposterior (AP) and lateral (L) projections between the talus (red), calcaneus (blue), first metatarsal bone (green), navicular bone (black), proximal phalanx of hallux (orange), and second metatarsal bone (pink). Some relationships vary with age, such as the talocalcaneal angle, which declines from 30 to 50 degrees at birth to 15 to 30 degrees by age 5 years. Other angles are stable, such as the pitch of the calcaneus at 20 to 30 degrees. *Subtalar joint incompetence, such as after overcorrection of clubfoot, may allow the calcaneus to slide lateralward from under the talus to produce hindfoot valgus while maintaining parallelism of the bones and thereby a reduced talocalcaneal angle. |
Uncouple ankle and subtalar joints when determining motion. Invert the hindfoot to bring calcaneus directly under talus and thereby lock the subtalar joint before flexing the ankle. Patients with contracture of triceps suræ will compensate for limited ankle flexion by swiveling through subtalar joint to place the foot flat on the ground. Flex and extend knee joint to isolate gastrocnemius muscle from soleus muscle. Ankle flexion >30 degrees is one criterion of ligamentous laxity. Flexibility of subtalar joint impacts deformity reconstruction. Deformity correction in the setting of a rigid joint is addressed by a compensating osteotomy or transarticularly by arthrodesis.
Imaging
While the foot lends itself to (hyper) analysis radiographically, there remains debate regarding applicability of metrics to functional outcome.
Röntgenogramme This is the mainstay [H]. Obtain views of weight bearing, because this is the functional position of the foot and foot shape varies significantly according to loading. There will be imprecision when drawing the longitudinal axis of irregular bones, such as the talus and calcaneus, and during growth with incomplete ossification.
Distinguish lateral view of the foot from lateral view of the ankle, which differs in the setting of deformity. Mortise view of the ankle delineates trochlea of the talus. Special views include oblique of the foot to view sinus tarsi and calcaneonavicular relationship and Harris view, which projects along the posterior facet of subtalar joint orthogonal to long axis of the calcaneus. Stress views may be useful in deformity, such as to distinguish oblique from vertical talus, and in trauma, such as Lisfranc injury.
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Other modalities Scintigramme reveals occult bone lesions, as in early osteomyelitis. Ultrasonography is useful for foreign body that may be radiolucent, such as glass, or operatively to aid and limit dissection. Computed tomography (CT) gives the finest bone detail, as in determining location and extent of tarsal coalition, and aids surgical planning, in particular with three-dimensional reconstruction. Magnetic resonance imaging (MRI) provides the best view of soft tissue, as in tumor; can expose osseous reaction to disease; and aids in the evaluation of mixed lesions, such as osteochondritis dissecans.
TOE DISORDERS
Toe anomaly may be isolated or part of a generalized disorder [A]. They hurt, can be unsightly, and interfere with shoe wear.
Syndactyly
This affects the 2nd to 3rd more than the 4th to 5th toes and often is bilateral. The skin bridge may be complete, involving the nails, or incomplete, receding variably from the nails. Isolated toe syndactyly is benign: it is asymptomatic and poses no dysfunction. Educate parents that release to improve appearance is outweighed by surgical risk and scar. The condition may be part of polydactyly.
Polydactyly
This is summarized in [B]. Familial form follows autosomal dominant inheritance with variable penetrance.
Postaxial polydactyly is subclassified into type A, in which a wellformed extra digit articulates with the 5th or a 6th metacarpal, and type B, characterized a rudimentary extra digit (pedunculated postminimi). A heterozygous mutation in the GLI3 gene on 7p14.1 has been found in both type A and type B. Autosomal dominant inheritance type A has been mapped to 7q22, 13q21, and 19p13. An autosomal recessive type A has been mapped to 13q13. Postaxial polydactyly is a feature of three-fourths of patients with trisomy 13.
In preaxial polydactyly, the metatarsal bone may be duplicated or widened to present a partial or separate condyle for the supernumerary digit. Mutation of the binding sites for transcription factors SOX9 and PAX3 in the LMBR1 gene (sonic hedgehog family) on 7q36.3 has been found in preaxial polydactyly. Preaxial hallucal polydactyly is a feature of diabetic embryopathy.
Operation is indicated toward the end of the first year, as a balance between osseous development and independent walking. Excise the less developed supernumerary digit, which may be determined by the nail, overall toe size, or radiographic appearance. Include partial or complete metatarsal resection to avoid prominence laterally or a wide web space centrally. The latter also may be ameliorated by reconstruction of the intermetatarsal ligament. Plan flap(s) or skin graft for associated syndactyly.
Bracket epiphysis This represents medial extension of the physis of hallucal phalanx or metatarsal to give origin to a preaxial polydactyly [C]. Growth of the epiphysis results in a broad-based bone that resembles a “triangle,” hence the original name “delta phalanx,” after the Greek letter Δ.
The epiphysis and physis are radiolucent but may be seen on MRI. Excision includes proximal extension to resect the physial bracket, along with release and reconstruction of remaining hallux to avoid varus deformity.
Curly Toe
The toe is flexed and rotated along its longitudinal axis under the next medial toe due to flexor contracture. This affects the lesser toes and often is bilateral. Half resolve spontaneously with walking. Deformity persistent beyond age 4 years is treated by flexor tenotomy at proximal cutaneous crease.
Presentation in the second decade may require complex reconstruction due to secondary contracture, including capsulotomy without or with flexor to extensor transfer. In the Girdlestone-Taylor procedure, the flexor is harvested via distal and proximal interphalangeal incisions, retrieved through a dorsal incision, through which a capsulotomy may be performed and where the tendon is sewn to the extensor.
Claw Toe
This is defined as metatarsophalangeal hyperextension with interphalangeal flexion [D]. It is a feature of extensor recruitment alone or in the setting of neural disease, where flexors are unopposed. Evaluation and management do not occur in isolation but are directed at the primary cause, such as cavovarus foot.
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 C Bracket epiphysis This rare form of preaxial polydactyly requires recognition, complete resection (red) to include part of the U-shaped physis and epiphysis (yellow), and reconstruction to avoid hallux varus. |
 D Defining deformity C: claw. H: hammer. c: curly. M: mallet. Note that a curly toe, in addition to interphalangeal flexion like a hammer toe, adds an axial deformity. |
 E Butler procedure Incision (red) allows for derotation and plantad displacement of the toe. Extensor tendon (green) is sectioned, as is the dorsal MP capsule (white). |
 F Bunion Hallux is deviated away from midline (green) and rotated (blue) against the second toe. The metatarsal head is prominent, and overlying soft tissues are reactive (red). |
 G radiographic assessment of bunion Note obliquity of metatarsocuneiform articulation. |
 H Osteotomies for bunion Distal osteotomy to correct DMAA is combined with medial soft tissue reconstruction. Opening wedge proximal osteotomy addresses increased IMA. While the distal exsected bone (green) may be transferred as shown on left, allograft (red) is more stable and can be tailored given that distal and proximal deformities rarely are equivalent. Alternatively, the proximal osteotomy may be made in the medial cuneiform (blue) if this is trapezoidal and the metatarsocuneiform articulation is inclined. The correction is fixed with a medullary wire that may be supplemented with a crossed wire for rotational control. |
Hammer Toe
This is defined as flexion deformity of the proximal interphalangeal joint (PIP). Metatarsophalangeal and distal interphalangeal (DIP) joints are obligatorily extended to contact the ground. Second toe is most affected. Presentation includes callus over dorsum of PIP joint and tends to be delayed into the second decade, when rigid deformity necessitates Girdlestone-Taylor procedure or PIP arthrodesis.
Mallet Toe
The essential lesion is fixed flexion deformity of the DIP joint. Presentation and treatment are similar to those of hammer toe
Overlapping Toe
Overlapping of the 2nd to 4th toes are benign and resolve spontaneously in infancy.
Digitus minimus varus Proximal and dorsal migration, with adduction and rotation to present the nail lateralward, of the 5th toe to overlap with the 4th typically is fixed. Operative correction (Butler) includes the following [E]:
Circumferential incision (be careful of neurovascular bundles!) at base of toe with dorsal limb centered on metatarsal and longer plantar limb at border of glabrous skin
Section of extensor tendon
Section dorsal metatarsophalangeal capsule
Rotation of cutaneous flaps to reinforce and maintain reduction of the toe
Bunion
Greek βºvvιºv: “small hill, tumulus,” whence “bunny,” describes the prominence of the head of metatarsal bone [F]. Childhood bunion represents a primary growth disturbance of the hallucal metatarsal, reflected in the appellation metatarsus primus varus. This may be quantified by the distal metatarsal articular angle (DMAA) and further revealed by trapezoidal deformity of the medial cuneiform. In neuromuscular patients, bunion may result from imbalance of muscle forces. In adult bunion, exogenous factors conspire to deform and destabilize the static and dynamic metatarsophalangeal soft tissues.
Evaluation The ratio of girls:boys is 5:1. A family history in half of patients suggests mendelian inheritance with variable penetrance. The hallux deviates away from midline and rotates such that the nail inclines medialward, eventually lying under or over the second toe. Soft tissue over the exposed and prominent head of metatarsal is callused, red, and sore. Pain also may be felt over displaced plantar sesamoids. Assess hypermobility of the first ray at the metatarsocuneiform articulation. Patients may present in the absence of pain or dysfunction due to cultural disapprobation.
Röntgenogrammes quantify deformity, form the basis for surgical indications, and guide operation [G].
Management Education is fundamental, including wearing of shoes with a sufficiently wide toe box and minimizing heel height. Orthotics do not provide a durable result.
Surgical treatment may be divided into four according to site and aspect of deformity corrected. There are numerous techniques and combinations, which betrays the facts that bunion is not homogeneous and that no single procedure is universally effective [H].
Soft tissue. This includes plication of medial capsule and release of adductor hallucis laterally. The former may be performed through drill holes for security. Beware of the first dorsal metatarsal artery, which enters the head on the lateral side. Following the principle that soft tissue reconstruction will fail in the setting of osseous deformity, combine this with osteotomy.
Osteotomy—distal. This is indicated when there is no proximal deformity. It corrects the DMAA and hallux valgus when the intermetatarsal angle (IMA) is normal.
Osteotomy—proximal. Indication is abnormal IMA. Opening wedge adds length to a short 1st metatarsal.
Base of metatarsal to medial cuneiform arthrodesis. This allows plantar flexion (in addition to coronal correction) of the metatarsal to address hypermobility of the first ray, in order to stabilize the medial limb of the tripod in flatfoot.
The principal complications are avascular necrosis of the head of metatarsal and over-/undercorrection. The former is related to lateral dissection. The latter are related to maturity in the uninvolved child, in whom operation should be delayed until physial closure. In neuromuscular disease, metatarsophalangeal arthrodesis balances control of correction against reduced physical demand.
Bunionette
This also is known as tailor’s bunion, after repetitive pressure and rubbing at the dorsal aspect of the 5th metatarsal head in the cross-legged position on an unyielding surface. The deformities mirror bunion on the opposite side of the foot. The disorder is less common and less troubling than is bunion in children. As a result, it rarely comes to surgery, which consists of the 5th metatarsal osteotomy to reduce prominence of the head.
Dorsal Bunion
The head of the 1st metatarsal is prominent at the dorsum, with associated flexion contracture of the metatarsophalangeal joint. An imbalance between a stronger tibialis anterior muscle than peroneus longus muscle lifts the 1st metatarsal. It may be a consequence of operative release of clubfoot, in which tibialis anterior may be hyperactive and a weakened triceps suræ is compensated for by flexor recruitment. Surgical management includes the following:
Flexion osteotomy of the 1st metatarsal or medial cuneiform, to correct deformity
Plantar metatarsophalangeal joint capsular release
Transfer of flexor hallucis longus to the neck of the 1st metatarsal (reverse Jones), to support correction and to reduce metatarsophalangeal joint flexion
Transfer of tibialis anterior to lateral cuneiform bone
Hallux Rigidus
The hallux does not move due to arthritis of the metatarsophalangeal joint. Dorsiflexion is lost first. Presentation is in the second decade. Repetitive trauma, osteochondritis dissecans (OCD), and hypermobile first ray have been implicated. Pain may be elicited with motion under resistance, in particular during standing on the metatarsal heads. Röntgenogrammes show signs of degeneration, including reduction in joint width, osteophyte, and possible OCD of the metatarsal head.
Initial treatment is supportive, including stiff shank or insert to limit metatarsophalangeal joint motion. Surgical options include the following:
Joint débridement, including cheilectomy, to alleviate pain and improve motion.
Metatarsophalangeal arthrodesis. This eliminates pain, is durable, and allows a high level of function in an active adolescent.
Hallux Varus
The hallux points medialward. Acquired deformity results from overcorrection of bunion. Congenital hallux varus may be dynamic or static. The former is due to overactivity of abductor hallucis muscle and is self-limited in infancy. In the latter, a palpable contracture of the muscle may become visible under the medial skin with abduction of the forefoot (Lichtblau test). Surgical release of abductor hallucis may be reinforced by lateral transfer of extensor brevis tendon.
Macrodactyly
This may be isolated [I] or associated with other condition, including Proteus syndrome, neurofibromatosis, or vascular malformation. It interferes with shoe wear, is readily traumatized, and is unsightly. Accommodate by modifying shoe wear. Physiodesis has limited utility, for example, it limits length but does not address width. Debulking is ineffective. Consider amputation of metatarsal as well as affected toe, in order to avoid a wide web space for adjacent toes to incline toward and create secondary deformity.
 I Macrodactyly There is hypertrophy of the entire second ray (red), which should be included in a resection. |
 A Metatarsus adductus Lateral border of the foot is curved (red). Heel bisector passes through the fourth web space |
 B Lengthening of brachymetatarsia The 4th metatarsal is short (orange). An external fixator is placed, the bone is cut at proximal metaphysis (red), and lengthened (yellow) with intervening callus. |
 A Midfoot:heel contact area Ratio of the arch width to the heel width varies with age. Normal mean is 0.5, and range is 0.25 to 0.75. Below this range is cavus (red). Above this range is flat (blue). |
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FOREFOOT
Metatarsus Adductus
The metatarsus is “directed” (Latin ducere) “to(ward)” (Latin ad-) the midline. This is one cause of in-toeing. It may be a “packaging sign” of uterine crowding, in association with plagiocephaly, torticollis, and hip dysplasia.
Evaluation The lateral border of the foot is curved [A]. The heel bisector, which normally passes through the second toe, is displaced lateralward with increasing severity. The deformity may be flexible or rigid, which some distinguished by the appellation metatarsus varus. Flexible metatarsus adductus is divided into active, which corrects with stimulation of the foot, and passive, in which the lateral border may be straightened and made concave by displacing the forefoot lateralward with one hand while securing the heel in the other hand. The hindfoot and ankle are supple.
The natural history is spontaneous resolution in > 90%. Rigid or persistent metatarsus adductus may interfere with shoe wear.
Management Education about the benignity of the condition is the cornerstone. Modalities such as stretching exercises in the first year and reversing shoes after walking age do not adversely impact the child and give parents some agency.
Rigid deformity is treated according to age.
Under 5 years, serial casting. A sequela is recurrence.
After 5 years, opening wedge cuneiform osteotomy with structural allograft and closing wedge cuboid osteotomy (bone is too cancellous to be structurally effective) with internal fixation. Tarsometatarsal capsulotomies with metatarsal osteotomies (Heyman-Herndon) is an unnecessarily complex procedure fraught with complications.
Brachymetatarsia
This may affect the hallucal metatarsal, as an atavic trait representing regression from a structure adapted for terrestrial erect weight bearing and locomotion to one adapted for arboreal life, in which the hallux more closely resembles an opposable thumb in relative size, position, and mobility (Morton foot).
Lesser brachymetatarsia typically affects the 4th toe, which is displaced proximalward and dorsad, furrowing the web space. Severe deformity is characterized by transfer metatarsalgia and pressure against the upper toe box. Two surgical techniques have been advocated:
Osteotomy and acute lengthening over a medullary wire, with intercalary bone graft. Autograft necessitates a second incision; allograft may not unite. Length is limited by soft tissue envelope, including toe ischæmia.
Osteotomy and callus distraction by external fixator [B]. This carries pin-site risks but, because it is gradual, it is more potent and less threatening to the adjacent neurovascular structures.
MIDFOOT
Cavus
Latin cavus describes a medial longitudinal arch that is “hollowed out,” as a “cave” is in the earth. While arch height is difficult to measure, the reduction in contact area that follows may be measured in the ratio of midfoot width:heel width [A]. Cavus may be divided into physiologic and pathologic. Physiologic is an isolated finding at one end or 2.5% above the Gaussian distribution for the general population. Pathologic is neuromuscular or syndromic [B].
Evaluation The essential problem in cavus is reduction of contact area (A), which increases pressure (P) for the same force (F) of body weight after the formula P = F/A. The foot hurts and reacts by forming calluses to increase the contact area [C].
In isolated cavus, the hindfoot is uninvolved. Determine flexibility of cavus, toes, subtalar, and ankle joints. Triceps suræ contracture may result in recruitment of the long digital extensors, which are visible under the dorsal skin, leading to flexible claw toes. Hindfoot varus displaces callus lateralward. It also stresses the ankle, including episodes of instability. Callus also appears over the dorsa of the clawed toes. Severe and rigid deformity is difficult to shoe.
Rule out other disease. The history may be obvious in an established diagnosis such as cerebral palsy. A family history may reveal a peripheral neuropathy. The child should be undressed and in a gown. Examine all systems, in particular the rest of the skeleton (e.g., other deformity), nervous (e.g., diminished deep tendon reflexes in peripheral neuropathy), muscular (e.g., weakness or wasting), and cutaneous (e.g., sign of dysrrhaphism). Unilateral deformity and hindfoot deformity are abnormal. Clawing of the toes may be a sign of intrinsic muscle disease.
Röntgenogrammes aid the determination of site(s) and severity of deformity, and operative planning. Consider other testing based upon index of suspicion. MRI may reveal a spinal cord tumor. Electrodiagnostic and gene testing are indicated for Charcot-Marie-Tooth diseases and muscular dystrophies (cf. Neuromuscular Diseases). Appropriate referral, for example, to a neurologist, completes the evaluation.
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