At the apex of the foot arches there are six wedge-shaped bones: three metatarsals and three tapered cuneiform bones (I–III) that have the same role as the single elements of an architectural arch. This cuneiform principle gives the foot great stability because the cuneiform bones press more and more against each other as the weight increases, so long as the heel takes this weight evenly (see Fig. 9.3).

The spiralled arch of the foot goes from ‘vertical back lateral’ to ‘horizontal front medial’. This is similar to the wringing out of a cloth, where the hands turn in opposite directions twisting between the two poles. This spiral principle of the foot can be seen when the heel is erect and the MTP joint of the big toe has complete contact with the ground. The arch goes evenly from the outside of the heel to the MTP joint of the big toe – the heel is in eversion (supination) and the forefoot in inversion (pronation) (see Fig. 9.4).

The muscles, ligaments and the connective plantar aponeurosis provide a stability that stretches triangularly from the calcaneus to the MTP joints. The height of the longitudinal arch is held in balance largely by the three muscles tibialis posterior, tibialis anterior and peroneus longus. They are supported by the triceps surae, flexor hallucis longus and flexor digitorum longus. The short muscles of the foot, such as abductor hallucis, flexor hallucis brevis, flexor digitorum brevis and abductor digiti minimi, are also involved (cf. Zukunft-Huber et al. 2011).

The five joints at the base of the toes form a flat transverse arch, like the letter C. Between them there are dozens of small foot muscles, e. g. interossei pedis, lumbricals, flexor hallucis brevis, adductor hallucis and flexor digiti minimi brevis. These muscles provide for the bending of the MTP joints and the elastic bracing of the forefoot arch. When weight bearing, it is pushed flat on the floor – the muscles between the bones also act as shock absorbers. When rolling the foot from heel to toe in walking, these small muscles are stretched, and then they contract in a reflex manner. This gives the foot forward propulsion while walking. If the shock absorber effect in the forefoot is missing, the knees and hips take a greater strain (see Fig. 9.5).

The feet provide a relatively small base when standing. It is however possible for us to organise the body on this small base without losing balance, owing to our differentiated motor adaptation (cf. Nacke 2005).

In DEB the dermatological requirements due to the complications of blistering, sores, adhesions, etc. are dominant over the biomechanical principles. The feet need to take the forces of weight bearing, shearing forces and friction, and so the skin is often in a very bad state and requires bandaging.

Adhesions and webbing of the toes and the impossibility of normal weight bearing on the soles of the feet lead to secondary changes in the skeleton and to muscle atrophy, especially the small muscles which are important for the movement of the toes and the weight shifts during locomotion.

In particular the MTP joint of the big toe may cause problems. It is the impetus for the lift-off movement of each step, and is often unable to take on this function fully because the state of the skin in usually very bad due to the extreme pressure to which this joint is exposed. In addition, contractures in the area of the MTP joints may also play a role.

As with the hands, the toes can become encased in a so-called cocoon (see Fig. 9.6). Spreading out the toes in this situation is impossible, and this leads to an atrophy of the lumbricals and the interossei plantaris and dorsalis.

The pelvis is the pivot between the straightened spine and the legs and feet below it. A centred pelvis is the prerequisite for a stable and physiologically correct starting posture for fluid and economic movement. Finding the dynamic centre is an important prerequisite for any activity in an upright position.

To be able to tilt the pelvis into an erect position, the lower back must be relaxed and stretched. The coccyx should be pulled down towards the heels and at the same time the pelvic floor will be activated. The pelvis will tilt up and the hollow back will disappear. The deep abdominal muscles will be activated, while the superficial abdominal muscles and buttocks will remain relaxed (see Fig. 9.7.a,b).

The axes of the legs should be as straight as possible between the two poles – feet and pelvis. When a child stands the inner sides of the knees and ankles should just touch, then the legs are parallel and symmetric and the patellae point directly forwards. If only the knees or only the ankles touch each other, then the child has either knock-knees or bow-legs (see Fig. 9.8a,b). It can also be that only the lower legs are not straight; that is called tibia vara.

Newborns very often have a harmless deformity of the feet, such as pes adductus (pes metatarsus varus) or pes calcaneus (talipes calcaneus). The feet were pressed tightly in the confined space of the uterus; this grows out quite naturally in the first month. Sometimes an unnatural shape remains; this can be improved or corrected during childhood.

A baby trains the development of the arches by bringing the foot, especially the big toe, to the mouth. The flexion of the hip joints in abduction and external rotation, the flexion of the knee and the supination of the foot foster the development of the three-dimensional arched structure of the foot (cf. Zukunft-Huber et al. 2011).

The foot bones of the infant are still soft cartilage and without the recognisable arches. This congenital flatfoot changes once the infant begins to bear weight. The foot develops from the inside once the muscles are activated by weight bearing, and during the process of learning to walk the arches take shape. Children experiment with different ways of standing, e. g. on tiptoe, until their sensory perception enables them to find a stable position (cf. Köhler, Reber 2006). For the development of a varied motor function of the foot it is important to walk with bare feet as much as possible. In the infant the tibia forms a plateau, which means that the knee cannot be completely extended. This gives the impression of bow-legs, which like the flatfoot disappear during growth.

In toddlers bow-legs or knock-knees are connected to the state of growth of the legs and are normal. They change from one to the other and show the complexity of growth dynamics (see Fig. 9.9).

By the time of transition from toddler to child, about the same time as the milk teeth begin to loosen, the leg and foot positions should have normalised: the feet should be parallel and the patellae facing forward when standing.

There are, however, many children who continue to have these leg positions after this age and do not stand straight. When standing on tiptoe the pull of the lower leg muscles should put this right (cf. Kempf, Fischer 2004).

Ideally, schoolchildren should have straight legs and the arches of the feet should be fully developed (see Fig. 9.10).

Unfortunately, this is frequently not the case. Poor shoes and too little weight bearing with low demands of motor adaptation leave the feet underdeveloped. The most common malpositions are pes planovalgus or talipes cavovalgus.

(See Fig. 9.11.a,b)

The way the positioning of the feet and the axes of the legs develop will depend on the EB type and sub-type, and the corresponding weight-bearing abilities of the feet. This may result in anything from a typical physiological position to a severe malposition.

Sensorimotor perception is reduced by the constant bandaging of the feet when a toddler with EB learns to walk.

Incorrect leg axes and position of the pelvis are the results of relieving postures of the lower extremities because of the limited weight-bearing capacity.

In severe cases of EB the feet are placed only very carefully on the ground, depending on the condition of the skin. In this way no active erect alignment of the pelvis develops and it remains tipped forwards. The knees have a tendency to knock, the thighs are rotated inwards and the foot arches are flattened. There is an apparent knock-knees position of the legs.

The pes or talipes valgus is the most common and severe malposition in children. The classical type is turned inwards. Looked at from the back there is a curved axis from the heel towards the calf. The talipes valgus can be on one or both feet. The heel takes the weight incorrectly, and so forces bring about a distortion of the arches; in time they become flattened.

The second type, pes or talipes varus, shows a tipping of the calcaneus in the opposite direction (see Fig. 9.12b).

The footprint when standing is a good indication of the functional height of the arch. In a normal case, the narrowest place, the isthmus, is one third of the forefoot. In the case of fallen arches, it is two thirds of the width of the forefoot, and with flatfoot the isthmus is as wide as the forefoot. When the mid-foot is even wider than the forefoot, it is called pes planovalgus.

In the pes planovalgus the arch has no torsion, the screw principle of the bones is weakened, the cuneiform bones become unstable, and the arches are completely flattened and nullified.

Pes excavatus presents a rigid immobile mid-foot with a high instep. The spiralling is exaggerated and too strong, presenting the opposite effect of a weakened spiral function as in flatfoot (see Chap. 9.6.2). Mostly, the toes take on a claw position.

There is also a form of the pes excavatus where the calcaneus tips medially; this is a combination of the pes valgus and the pes excavatus in which the foot muscles (quadratus plantae, abductor hallucis, abductor digiti minimi, and flexor digitorum brevis) have an extremely high tone.

The footprint of a high-arched foot is divided in two with a print of the balls of the toes and the heel; when standing, a pencil can be pushed through between these two contact points.

The pes transversoplanus is a result of a flattening of the transverse arch. There is no or little tonicity and elasticity of the muscles and tendons. The forefoot appears flat and the foot is unproportionately wide for its length.

The flattening of the transverse arch results in the toes being overextended and not lying flat on the ground. In time claw toes develop. In extreme cases there can be a subluxation of the MTP joints. The strain on the balls of the feet often results in the development of callus.