CHAPTER 13 The foot
Anatomical Features
Fig. 13.A. Tripod action of the foot:
To maintain perfect ground contact each foot acts as a tripod, with the legs of the tripod being represented by the calcaneus and the heads of the first and fifth metatarsals. To maintain balance, the centre of gravity (in front of S2) must fall within the area covered by one or both feet, and to facilitate this each foot must be capable of movement in two planes.
Fig. 13.B. Planes of movement (1):
In the x-axis nearly all of the movement occurs in the ankle, and this allows balance to be maintained when going up and down slopes. (Some very slight movement in the same plane occurs in the midtarsal and tarsometatarsal joints, and minimally in the subtalar joint.)
Fig. 13.C. Planes of movement (2):
In the z-axis supination (S) occurs when the soles of the feet are turned inwards to face one another; pronation (P) involves movement in the opposite direction. This allows the feet to adapt to a surface sloping at right angles to the direction of travel. The major part of this movement involves the subtalar joint (but the midtarsal and tarsometatarsal joints are also involved).
Fig. 13.D. Planes of movement (3):
In the y-axis, at right angles to the others, a very limited range of abduction and adduction of the forefoot may occur. Most of this occurs in the midtarsal joint, but some takes place in the tarsometatarsal joints and in the ankle. This is of relatively little importance, although a fixed metatarsus adductus is a well known, self-limiting deformity, generally of childhood.
Inversion of the heel occurs when the calcaneus tilts into varus. This movement occurs in the subtalar joint. As the heel tilts, it carries the rest of the foot with it (the foot is directly connected to the calcaneus through the calcaneocuboid joint), and this results in supination of the foot. (Valgus tilting of the heel (eversion) results in pronation of the foot.)
Fig. 13.F. Subtalar movements (1):
Movements in the subtalar joint, which involves two pairs of articular surfaces, are highly complex, the only joints they resemble being those between the radius and ulna. There is, however, a relatively fixed axis of movement which passes through the centre of the head of the talus in front, and through the posterolateral tubercle of the calcaneus behind.
Fig. 13.G. Subtalar movements (2):
The complex pattern of calcaneal movements that occurs in inversion are sometimes compared with the three-plane movements of ships or aircraft: the calcaneus rolls (1), pitches (2) and yaws (turns) (3) under the talus.
Fig. 13.H. The midtarsal joint (1):
This links the hindfoot with the midfoot. It is formed by the head of the talus (T) and the navicular (n) on the medial side, and on the lateral by the calcaneus (C) and the cuboid (c). The latter joint (Cc), which permits only a limited range of movements, ensures that when the heel moves the rest of the foot follows.
Fig. 13.I. The midtarsal joint (2):
The joint has in effect two axes of movement. First, it acts as a hinge, allowing slight dorsiflexion and plantarflexion (like the ankle). The axis of this hinge passes through the centre of the head of the talus, so that this movement is coordinated with subtalar movement (which passes through the same point). The plane of this axis is tilted at 45° relative to the horizontal.
Fig. 13.J. The midtarsal joint (3):
In addition to movements in (roughly) the x-axis, a limited amount of pronation and supination (z-axis) is possible; the navicular slides and rotates round the head of the talus, and the cuboid slides on the calcaneus. This axis of rotation also passes through the centre of the head of the talus.
Fig. 13.K. Tarsometatarsal movements:
(a) Whereas the heads of the first and fifth metatarsals form the anterior limbs of each foot tripod, the other metatarsal heads can adapt to any irregularity in the surface of the ground. Elevation and depression of the first metatarsal head and of the others (particularly the fourth and fifth (b)) can contribute an appreciable amount to overall supination of the foot (e.g. first tarsometatarsal movement amounts to 15°).
Normally, in the weightbearing foot the axis of the heel is in alignment with the tibia (a). If the heel posture is abnormal and tilts into varus, then under normal circumstances the foot would supinate and the first metatarsal head would not contact the ground (b). To correct this, the foot distal to the subtalar joint must pronate, and this leads to accentuation of the medial longitudinal arch (c).
If, on the other hand, the heel posture is one of valgus (d), then to allow all the metatarsal heads to contact level ground the foot distal to the subtalar joint must supinate, leading to flattening of the medial arch (e). The important practical points to note are that valgus heels are associated with flat foot, and varus heel with pes cavus
These are well known features of the foot. The medial longitudinal arch is the most important, and the one primarily affected in pes planus and pes cavus. It is formed by the calcaneus (C), talus (T), navicular (N), cuneiforms (Cn) and medial three metatarsals. Flattening of the arch is common and is assessed clinically, although weightbearing lateral radiographs may be helpful.
The medial arch is supported by the spring ligament (S), which shoulders the head of the talus; the plantar fascia (P), which acts as a tie; abductor hallucis (A) and flexor digitorum brevis, which act as spring ties; tibialis anterior (T), which lifts the centre of the arch (and, with peroneus longus (PL), forms a stirrup-like support for it); tibialis posterior (TP) which adducts the midtarsal joint and reinforces the action of the spring ligament; and flexor hallucis longus (FHL), which acts as a long spring tie and helps support the head of the talus.
The lateral longitudinal arch is formed by the calcaneus, cuboid and fourth and fifth metatarsals; it is very shallow, and generally flattens out on weightbearing. It is supported by the long and short plantar ligaments (LS), the plantar fascia (P), flexor digitorum brevis, flexor and abductor digiti minimi (not shown), peroneus tertius (PT), peroneus brevis (PB) and peroneus longus (PL).
The transverse arch is formed by the cuneiforms (c) and cuboid (cu). It stretches across the sole in the coronal plane. It is in fact a half arch: the whole arch is completed by the other foot. It is of no particular clinical significance, as its presence and size are precisely related to those of the medial longitudinal arch. The shape of the cuneiforms (likened to the voussoirs of stone arches) helps maintain the arch.
The anterior arch lies in the coronal plane; its bony components comprise the metatarsal heads. It is not a feature of the weightbearing foot, as under load the metatarsal heads flatten out. The metatarsal heads are prevented from spreading out (splaying) by the intermetatarsal ligaments (IM) and the intrinsic muscles, especially the transverse head of adductor hallucis (AH).
Extensor digitorum longus (EDL) extends the MP (metatarsophalangeal) and both IP (interphalangeal) joints of each toe. The interosseous and lumbrical muscles (L), through their attachment to the extensor expansions (E), extend the toes at the proximal and distal interphalangeal joints, and flex the MP joints; if they become weak or fail, the unchecked pull of flexor digitorum longus (FDL) results in clawing of the toes.
The relative length of the toes is subject to variations, many of which are regarded as normal. The commonest arrangement is the Egyptian foot (E), when the great toe is longest and the succeeding toes progressively shorter. In the so-called Greek foot (G), the second is the longest. In the rectangular or intermediate foot (R), the great and second toes (and often the third) are equal in length.
Conditions Commencing or Seen First in Childhood
Talipes Equinovarus (Club Foot)
This is the commonest of the major congenital abnormalities affecting the foot, and may be detected before birth by ultrasonography. All newly born children should be examined to exclude this condition. It is commoner in boys than girls, and the aetiology is uncertain. The deformity is a complex one: characteristically there is a varus deformity of the heel and adduction of the forefoot, accompanied by some degree of plantarflexion and supination. MRI scans are regarded as being of value in determining talonavicular alignment and as a guide to management.
The best results are obtained with early, aggressive conservative treatment, and in particular the long-established Ponseti regimen has been shown to be particularly successful in the management of this potentially very disabling condition. It involves manipulative stretching of the tightened structures (in practice, gently stretching the foot into as near normal alignment as possible) and applying a cast from the toes to the groin. This is repeated every 5–7 days, to better each correction. Once full correction has been obtained, the child is given an abduction foot orthosis which is worn full time for 12 weeks – and then at night and nap times. (Possible percutaneous tenotomy of the tendocalcaneus and transfer of tibialis anterior are integral parts of the protocol.)
In some cases, especially when there is a delay in starting treatment or where there is a failure to respond, simple measures may not be enough. More radical treatments include division of the plantar fascia at the heel and procedures that stretch the soft tissues and influence bone growth, especially those using the Ilizarov method (this involves the insertion of wires through bony elements in the leg and foot, connecting them with a frame, and repeatedly adjusting their spacing and orientation).
In untreated cases the primary anomaly affecting the soft tissues is followed by alteration in tarsal bone growth. In such cases, wedge excision of bone and fusion of the midtarsal and subtalar joints may be required to obtain a plantigrade foot (Dunn’s arthrodesis, triple fusion).
When an incomplete correction has been obtained, the commonest residual deformities seen in the older child and adult are persistent adduction of the forefoot, shortening of the Achilles tendon and some stunting in overall growth of the foot.
Talipes Calcaneus
This is a much less common congenital abnormality of the foot, in which the dorsum of the child’s foot lies against the shin. There are frequently associated deformities of the subtalar and midtarsal joints, with the heel lying in the varus or valgus position (talipes calcaneovarus, talipes calcaneovalgus). This condition is also treated by stretching and splintage as soon as the diagnosis has been made.
Skew Foot
In this condition there is adduction of the metatarsals (metatarsus adductus) accompanied by a valgus deformity of the hindfoot. It may be seen as a residual deformity in cases of club foot where treatment has not been followed by complete resolution, or it may occur on its own. Many cases resolve spontaneously, but in some it persists, leading to callosities and foot pain. Treatment is usually by conservative measures, but surgery may be required in resistant cases.
Intoeing
After walking has commenced, parents may seek advice because the child is walking with the feet turned inwards (intoeing, hen-toed gait). The feet may be internally rotated to such an extent that the child is constantly tripping and falling. Sometimes this may be due to torsional deformity of the tibiae (which must always be excluded), or be seen as a complication of cerebral palsy, but more often it is the result of a postural deformity of the hips (internal rotation) or excessive anteversion of the femoral neck. The condition generally corrects spontaneously by the age of 6. Continued observation is advised until correction occurs, but active treatment is seldom required.
Flat Foot
The arches of the foot do not start to form until a child starts walking, and they are not fully formed until about the age of 10; the young child’s foot is normally flat. Nothing is known to speed up the process of arch formation: orthopaedic shoes, heel cups and plastic moulded insoles have all been shown to be valueless. Failure of establishment of the arches is quite rare, but if this occurs it can lead to awkwardness of gait, rapid, uneven wear and distortion of the shoes, but seldom pain or other symptoms if joint mobility is preserved. Persistent flat foot may be associated with valgus deformities of the heel, knock knees, torsional deformities of the tibiae and shortening of the Achilles tendon. Rarely it may result from an abnormal talus (vertical talus) or neuromuscular disorders of the limb (e.g. poliomyelitis, muscular dystrophies). In the older child, gross deformities with a clear organic basis may require surgery, the nature of which is dependent on the pathology (e.g. calcaneal osteotomy for severe valgus heels).
Pes Cavus
Abnormally high longitudinal arches are produced by muscle imbalance, which disturbs the forces controlling the formation and maintenance of the arches. In many cases there is a varus deformity of the heel and a first metatarsal drop (an increase in the angle between the first metatarsal and the tarsus). Two distinct groups are seen: those in which subtalar mobility is maintained, and those in which subtalar movements are decreased or absent. A neurological abnormality should always be sought, and sometimes this may be obvious (e.g. spastic diplegia or old poliomyelitis). Many cases are associated with spina bifida occulta, which may be confirmed by clinical and radiological examination. Rarely fibrosis of the muscles of the posterior compartment of the leg from ischaemia may be the cause. In the more severe cases there is weakness of the intrinsic muscles of the foot, with clawing of the toes; the abnormal distribution of weight in the foot leads to excessive callus formation under the metatarsal heads and the heel.
When the deformity is marked, surgery is indicated to relieve symptoms and lessen the chances of ultimate skin breakdown under the metatarsal heads. Where there is a varus deformity of the heel, correction of this defect alone may give good results; in some cases a wedge osteotomy of the distal tarsus or metatarsal bases is required to flatten the highly curved arch and improve the weight distribution in the foot. Where clawing of the toes is the most striking finding, proximal interphalangeal joint fusions of the toes or transplanting the flexor into the extensor tendons may be helpful.
Kohler’s Disease
This is an osteochondritis of the navicular occurring in children between the ages of 3 and 10. Pain of a mild character is centred over the medial side of the foot. Symptoms settle spontaneously over a few months and are not influenced by treatment.
Sever’s Disease
Chronic pain in the heel in children in the 6–12-year age group generally arises from the calcaneal epiphysis, which radiologically often shows increased density and fragmentation. The condition is usually referred to as Sever’s disease which, although originally considered to be an osteochondritis, is now believed to be due to a traction injury of the Achilles tendon insertion. Symptoms settle spontaneously without treatment.
Conditions Affecting the Adolescent Foot
Hallux Valgus
In adolescence, and particularly in girls, where there is competition between the rapidly growing foot, tight stockings and often small, high-heeled, unsuitable shoes, valgus deformity of the great toe first appears. In some cases a hereditary short and varus first metatarsal may contribute to the problem. As the deformity progresses, the drifting proximal phalanx of the great toe uncovers the metatarsal head, which presses against the shoe and leads to the formation of a protective bursa (bunion), often associated with recurrent episodes of inflammation (bursitis). The great toe may pronate, and further lateral drift results in crowding of the other toes; the great toe may pass over the second toe or, more commonly, the second toe may ride over it. The second toe may press against the toe cap of the shoe, where there is little room for it, and develop painful calluses. Later it may dislocate at the metatarsophalangeal joint. The sesamoid bones under the first metatarsal head may sublux laterally, leading to sharply localised pain under the first metatarsophalangeal joint. In the late stages of the condition, arthritic changes may develop in the metatarsophalangeal joint. More commonly, there is associated disturbance of the mechanics of the forefoot, leading to anterior metatarsalgia.
A number of surgical procedures are available to correct hallux valgus deformity. The most popular are (a) fusion of the metatarsophalangeal joint in a corrected position; (b) Keller’s arthroplasty (excision of the prominent part of the metatarsal head and removal of the basal portion of the proximal phalanx); (c) osteotomy of the first metatarsal neck (Mitchell operation); and (d) in early cases, simple excision of the prominent part of the metatarsal head may give relief. Silicone replacement of the metatarsophalangeal joint is no longer advocated, as it has been found that a troublesome silicone granuloma almost invariably develops in the region within 4 years of surgery.
Peroneal (Spastic) Flat Foot
In adolescents (boys in particular), painful flat foot may be found in association with apparent spasm of the peroneal muscles. The foot is held in a fixed, everted position. Inversion of the foot is not permitted, and there is often marked disturbance of gait. The condition is frequently associated with ossification in a congenital cartilaginous bar bridging the calcaneus and navicular (tarsal coalition). This anomaly may be demonstrated radiologically. Surgery in the form of excision of the bar is now the normal treatment for this condition.
Exostoses
Apart from the exposure and prominence of the medial side of the first metatarsal head commonly seen in association with hallux valgus (and referred to as a first metatarsal head exostosis), several exostoses may give rise to trouble in adolescence:
Conditions Affecting the Adult Foot
Hallux Rigidus
Primary osteoarthritis of the metatarsophalangeal (MP) joint of the great toe often commences in adolescence and gives rise ultimately to pain and stiffness in this joint. It is commoner in males, and is not associated with hallux valgus. Sometimes the toe is held in a flexed position (hallux flexus), and the proximal phalanx and metatarsal head are thickened following joint narrowing and circumferential exostosis formation. Treatment is usually by fusion or Keller’s arthroplasty.
Adult Flat Foot
Gradual flattening of the medial longitudinal arch (incipient flat foot) may occur in those who spend much of the day on their feet. This is often associated with an increase in body weight and the degenerative changes of ageing in the supporting structures of the arch. When these changes are rapid, they give rise to pain (‘medial foot strain’). Secondary (tarsal) arthritic changes may also give rise to pain in long-standing flat foot, and are associated with loss of movement in the foot (rigid flat foot). Nevertheless, in two-thirds of cases of flat foot mobility is preserved in the ankle, subtalar and other foot joints (flexible or mobile flat foot), and there is no cause for clinical concern or significant potential for disability. (Ballet dancers and many professional footballers have grotesquely flat feet which do not interfere with their activities.)
In the early stages incipient flat foot may be helped by weight reduction, physiotherapy and arch supports. In the later stages, surgical shoes with moulded insoles may be the most helpful measure.
Splay Foot
Widening of the foot at the level of the metatarsal heads is known as splay foot. This may occur as a variation in the normal pattern of foot growth, causing no difficulty apart from that of obtaining suitable footwear. Splay foot may also be seen in association with metatarsus primus varus, hallux valgus and pes cavus.
Anterior Metatarsalgia
In anterior metatarsalgia there is complaint of pain under the metatarsal heads. The condition is particularly common in middle-aged women and is also often associated with some splaying of the forefoot. Symptoms may be triggered by periods of excessive standing or an increase in weight, and there is often a concurrent flattening of the medial longitudinal arch. Weakness of the intrinsic muscles is usually present, so that there is a tendency to clawing of the toes; hyperextension of the toes at the MP joints leads to exposure of the plantar surfaces of the metatarsal heads, which give high spots of pressure against the underlying skin. In turn this produces pain and callus formation in the sole. This pathological process is by far the commonest cause of forefoot pain, but in every case March fracture, Freiberg’s disease, plantar digital neuroma and verruca pedis should be excluded.
The majority of cases of anterior metatarsalgia respond to skilled chiropodial measures, which may include trimming of calluses and the provision of supports: these distribute the weightbearing loads more evenly under the metatarsal heads. Where there is much splaying of the forefoot and associated toe deformities, surgical shoes may be required. Where there is a marked hallux valgus deformity an MP joint fusion may improve the mechanics of the forefoot, with relief of pain.
March Fracture
This occurs in young adults and involves the second or, less commonly, the third or fourth metatarsals. The fracture usually follows a period of unaccustomed activity (there is no history of injury) and pain settles after 5–6 weeks when the fracture unites.
Freiberg’s Disease
This is an osteochondritis of the second metatarsal head associated with palpable deformity and pain. Pain may persist for 1–2 years, and in severe cases excision of the metatarsal head may become necessary. Excellent results have also been claimed for a dorsiflexion osteotomy of the metatarsal neck.
Plantar (Digital) Neuroma (Morton’s Metatarsalgia)
A neuroma situated on one of the plantar digital nerves just prior to its bifurcation at one of the toe clefts may give rise to piercing pain in the foot. It most commonly affects the plantar nerve running between the third and fourth metatarsal heads to the third web space, but any of the digital nerves may be affected. It most commonly occurs in women, particularly in the 25–45-year age group, and is often treated by excision of the affected nerve. Division of the intermetatarsal ligaments in the affected space without excising the nerve is said to give comparable results.
Verruca Pedis (Plantar Wart)
Verrucae, thought to be viral in origin, are common in the metatarsal region, the great toe and the heel. They must be differentiated from calluses, and are most frequently treated by the careful application of caustic preparations such as salicylic acid, acetic acid and carbon dioxide snow.
Plantar Fasciitis
Pain in the heel due to plantar fasciitis is a common complaint in the middle-aged. The condition is related to degeneration of the plantar fascia at its attachment to the medial calcaneal tuberosity. The condition has been described as having three stages. Initially there is a traction periostitis of the medial band of the plantar fascia, causing local heel pain. In the more advanced second stage, the posterior tibial nerve may be involved, giving rise to the symptoms and signs typical of tarsal tunnel syndrome. In the third stage, the tibialis posterior tendon may be affected, causing the occurrence of tenderness along the line of its course behind and beneath the medial malleolus and at its insertion in the navicular. There is seldom difficulty in making a diagnosis from the history and clinical findings, but local thickening of the plantar fascia may be confirmed by MRI scans or ultrasound examination. Symptoms tend to be prolonged, and the first aim of treatment is to reduce stress on the plantar fascia. Measures include weight loss, the wearing of lacing boots with small heels, night splints and orthoses. Extracorporeal shock wave therapy (ESWT) has been shown to be effective, but the use of NSAIDS and local steroid injections is no longer advised. In persistent cases, surgery in the form of fasciotomy of the medial band of the plantar fascia may be considered.
Mallet Toe, Hammer Toe, Claw Toe, Curly Toe
In a mallet toe there is a fixed flexion deformity of the distal interphalangeal joint of the toe; in a hammer toe there is a fixed flexion deformity of the proximal interphalangeal joint of a toe: the distal IP and MP joints are extended; in a claw toe both interphalangeal joints are flexed and the MP joint extended; and in a curly toe all three joints are flexed. In all these conditions corns may develop where the deformed toe presses against the footwear. Treatment may be conservative, by local chiropodial measures, or surgical, by means of interphalangeal joint fusions or, occasionally, in the case of mallet toe, by amputation. Simultaneous correction of an accompanying hallux valgus deformity may be required if a straightened second hammer toe is prevented from lying correctly because of the position of the hallux. Multiple clawed toes seen in association with pes cavus may be treated by IP joint fusions and flexor/extensor tendon transfers.
The Nail of the Great Toe
Ingrowing of the great toenail gives rise to pain and a tendency to recurrent infection at the nailfold. If infection is not a problem, skilled chiropody treatment (e.g. by nail training using a prosthetic device) is usually successful.
