Developmental problems

During the period in which the foot is growing a variety of interrelated problems can arise. These fall into two groups of significant problems but represent a relatively small percent­age of the total population. The vast majority of children presenting to a surgeon will in fact be normal. The major cause for presentation will be parental concern about perceived problems about the shape of the foot or abnormal shoe wear. The two groups of disorder, foot shape and func­tion, are the conditions leading to a progressive planovalgus (or flat) foot and those that lead to pes-cavus or a high arched foot. Some of the toe conditions start to become symptomatic in the childhood years but only in adolescence does the condition of hallux valgus appear as a significant developmental abnormality.

Planovalgus foot

The flat foot is normal providing that the longitudinal arch rises and falls dynamically. In activities such as standing on tiptoes the longitudinal arch rises. This is the basis of the clinical test of great toe dorsiflexion (Fig. 31.2). It is this that allows the body to store energy in the foot during walking. This in turn allows efficient, low-energy-cost locomotion.

The flat foot becomes pathological when one of three things happens. First, anything which stops movement in one of the joints of the hindfoot will simply prevent the normal behaviour of this mechanism. The condition of tarsal coali­tion is the most obvious example of this. This is where there is an abnormal join (fibrous or bony) between two or more tarsal bones.

Second, conditions which affect the integrity of the primary restraints of the various joints involved will result in instability. This leads to the foot deforming into a valgus heel position and into an abducted (and supinated) forefoot position. Conditions such as Marfan’s syndrome are examples of this form of problem. Commoner is familial hypermobility, but only a few of these patients exhibit pathological foot function.

Third, imbalance between the secondary restraints can cause progressive deformity. The best example of this is in neurological conditions such as cerebral palsy. Here the spasm in the peroneal muscle groups overcomes the action of the inverters of the foot. The hindfoot is gradually pulled into valgus. This in turn leads to stretching of primary restraints. If the deforming force is un-resisted for long enough, the effect is to produce bony deformity; this fixes the deformity. Although this pattern of developing deformity can be applied to the adolescent foot, it also underlies the pattern of development of a progressive planovalgus foot in any age group. In the elderly rupture of the tibialis posterior tendon will cause imbalance of the secondary restraints.

Treatment

  This will obviously be dependent on the underlying cause of the progressive deformity.

Primary treatment should always be conservative in nature. In the foot with increased mobility the use of orthoses will control the foot position while a shoe is worn. This diminishes the pressure on the foot created by the shoe; thus the symptoms due to pressure effects are reduced. The shoe itself is less likely to deform and produce abnormal wear contributing to the pressure on the foot. There is no evidence that such devices influence the long-term outcome for the foot. Corrective orthoses in conditions where the deformity is fixed, as in a coalition, do not work. In these circumstances orthoses should be used to increase the cushioning available in the foot. This can reduce symptoms by reducing the forces passing through the foot. Rest and modification of activity can have a profound effect on the symptoms that the patient experiences. This can mean that despite the rigidity of the foot the patient is pain free and has reasonable function. If the joints involved are irritable and painful an injection of a local anaesthetic agent with an intra­articular steroid injection can reduce symptoms until the child is older.

In the neurological conditions such as cerebral palsy, physiotherapy including stretching exercises has a role to play. This allows the imbalance to be corrected passively. The use of ankle foot orthoses to maintain the position of the foot is helpful (Fig. 31.3). If the increased tone in the peroneal and calf muscles is a particular problem then botulinum toxin injections into the muscle bellies can be useful. The effect wears off within days but during the period of reduced spasm the benefit of surgical treatment can be assessed in the knowl­edge that the paralysis will wear off in the fullness of time. During the period when the toxin is active physiotherapy may overcome the deformity further providing a longer-term benefit.

The principle of surgical treatment is first to balance the forces acting on the foot to remove the deforming forces; second, to correct any deformity that has already developed; third, to stabilise the foot in order to prevent deformity from recurring.

   Release of fixed deformity. This could be soft tissue (as in lengthening the peroneal tendons) or bony (as in the excision of a tarsal coalition).

  Correcting bony deformity. This can be achieved by lengthening the lateral border of the foot using a modified distraction osteotomy originally described by Dillwyn Evans (Fig. 31.4) or by an osteotomy of the os calcis design­ed to transfer the contact point of the calcaneum medially.

  Balancing the secondary restraints. This may involve tight­ening of the inverters of the foot. This may include formal reconstruction of the tibialis posterior tendon.

Reconstructing the primary medial restraints such as the talonavicular joint capsule.

  If these principles cannot be achieved then fusion of some or all of the joints of the hindfoot (as in a triple arthrodesis) will allow correction of foot position, reduce pain from damaged joints and prevent recurrence of the deformity.

Pes cavus

The mechanism of the generation of the deformity of the high arch foot is less easy to understand. This is partly because a number of conditions leads to similar although not identical deformity. The common feature of the condition is some element of neurological dysfunction. This leads to the problem of muscle imbalance. The intrinsic muscles are weak leading to a mismatch between the intrinsic and extrinsic muscle power. With equinus deformity the Achilles tendon is tight. This is not an invariable feature of pes cavus and in conditions where the calf muscles are weak there is a cal­caneus deformity. In addition there is a group of patients who have a relatively higher inverter power than everter power. This will lead to the foot rotating so that the lateral border is mainly in contact with the floor.

The clinical presentation of patients with pes cavus most commonly occurs in late childhood or early adolescence when the presence of the deformity becomes more obvious. The deformity is obviously influenced by growth but can progress after growth has ceased. Symptoms which are usually present are increased pressure on the forefoot due to clawing of the toes and equinus, pain on the lateral border of the foot due to a varus heel position and finally feelings of insecurity and weakness. Where there is an associated sensory neuropathy, patients can suffer with ulceration. Patients generally need to be monitored to analyse the rate and nature of progressive change.

Because of the variations in specific aetiology, and the progression and nature of the deformity, various management options need to be considered. The use of conservative treat­ment is important and largely revolves round the use of appropriate shoe ware. Shoes need to have extra depth to accommodate toe deformities. The sole needs to be cushioned to absorb the excess pressure. Adjustments can be made to the sole of the shoe with outside wedges to create a corrective force on the outer border of the foot. The same effect can be achieved with insoles. If conservative treatment fails then surgical options need to be considered. With any part of the deformity the first thing to consider is whether it is mobile or fixed. In general terms mobile deformities can be corrected by soft tissue surgery. Fixed deformity requires bony or joint surgery. An algorithm for the management of pes cavus has to be based on the type of deformity and the nature of the clinical complaint (Table 31.1).

Although this guide gives a concept of the procedures that have to be considered when treating the cavus foot, there is a great variation in the pattern of deformity with different aetiologies. The deformity can progress throughout life. This again has to be taken into account in planning the management of each individual case (Fig 31.5).