Part 12

Fig. 61.

Fig. 62.

Fig. 63.

Fig. 60.--Fouilloy's Braces. Figs. 61 to 65.--Marks' braces. Fig. 61.--General construction of the braces. Figures 62 and 63.--Attachment at the sides of the thigh piece. Figures 64 and 65.--General view of the apparatus as worn.]

To attach extension braces to the front of the leg piece the old and simple method adopted by Fouilloy may be used. It consists in attaching an elastic strap to the brace which passes over the shoulder on the side of the amputation (and which is fixed to the top of the thigh piece alongside of the other brace). The elastic strap ends in a bifurcated leather thong each branch of which (held in place by a loop of leather) descends obliquely alongside of the patella surface to be attached to the corresponding side of the leg in its upper third (Fig. 60).

In Marks' method the braces end below in loops made of a leather thong (Fig. 61). These are held against the thigh piece by passing under leather bands; they reach as far down as the upper third on the inner and outer sides of the thigh (Figs. 62 to 65).

To each of the loops, gliding on them by means of a pulley, is attached a leather strap which descends vertically to the upper third of the corresponding surface of the leg, being held in place by passing under a leather band. These two straps are attached to each other in front by a lace, which draws them towards the middle line, and in this way brings their line of action forwards. The tighter the lace is drawn the more powerful will be the extending force.

Instead of attaching the extension brace to the leg piece it may be made to pass under a pulley in the interior of the knee. What actually happens is that the thigh piece drops, owing to its weight, when the limb is swung free; this throws a strain on the brace which is transmitted to the leg piece by the following mechanism. The metal stop described on page 39 which limits extension of the knee during the period of weight bearing, is prolonged upwards and forwards beyond the hole through which the axis of the knee passes, this prolongation being furnished with two wooden pulleys (Fig. 69). The loops attached to the braces enter the front of the thigh piece, each by a separate opening, turn under the corresponding pulley and emerge again posteriorly (Figs. 66 to 68).

This mode of attachment has the advantage that when the limb is swung the movement does not take place upon the shoulders--which easily become chafed by the ordinary suspenders--but upon the pulleys upon which the leather thongs work.

The mechanism shown in figures 69 to 71 is interesting. When the metal lever moves around the axis of the knee joint, its lower end and the pulleys at the upper end travel in opposite directions: in flexion the pulleys move downwards and forwards, the lower end upwards and backwards; in extension they move in the opposite direction. Therefore when the limb is swung and the knee bends (Fig. 71), the thigh piece drops of its own weight, the braces tighten, raise the pulley and consequently make the lower end of the lever move downwards and forwards, thus extending the knee joint.

D. Mechanism to secure rigidity of the knee during weight hearing.--During the time that the healthy limb is raised from the ground and carried forwards there must be complete rigidity of the artificial limb in the extended position. This is secured by mounting the foot in the equinus position. When it has been swung forwards, in taking a step, the limb comes in contact with the ground heel first; then, as the leg becomes vertical the entire sole lies flat on the ground; if the foot is in equinus this position is only possible with the knee hyperextended, or with full extension it may be possible for a very short period. So that it is the weight of the body that locks the limb in the extended position, the sole of the foot sloping obliquely downwards and forwards; and the weight being taken on the toe. There is always a tendency to hyperextension, and to avoid straining the limb in this direction (as occurs in a living knee which is forced into the position of genu recurvatum by a talipes equinus) it is as well, as we have already said, to oppose it by some passive resistance, either in the form of a simple popliteal check cord or by a stop fixed to the front of the leg.

Fig. 73.

Fig. 74.

Fig. 75.

In Figure 72 the foot is fixed, the weight comes upon the point of the foot, and pressure upon the axis AB tends to close the angle ABC, i.e. to produce a genu recurvatum, and so to lock the knee in extension. If the foot is articulated, equilibrium is secured in the same way. Figures 73 to 75 are intended to show that in order that the axis ABC may not be vertical (Fig. 73) the axis B of the knee must be behind the perineal concavity in the bucket, and it is better if at the same time the axis of the ankle joint C is carried forward.]

This extension is unlocked automatically at the moment when the weight is thrown forward on the healthy limb, the artificial limb rising on its toe and the knee commencing to bend because the braces are relaxed.

E. Movable ankle.--We have taken as our type a limb with a fixed foot. There are, however, a number of methods of attaching a foot with a movable ankle joint. The general principles and the mechanism for securing stability are those which we have already studied, but the gait is more supple, at the price it is true of somewhat delicate articulations and therefore of simplicity.

The foot is made of a single piece of wood; it is divided transversely at the level of the middle of the metatarsal bones, and the anterior part (shaped like toes) is attached by two pieces of leather, dorsal and plantar, between which are two indiarubber cylinders which keep the toe piece extended 15° to 20° when at rest, and which allow, when the foot is pressed on the ground, an extension to 45°.

This foot is mounted on the leg at an angle of 45° beyond the right angle, with an interposed rubber cylinder, which allows of the diminution of the angle to 25° or 30° but no further. It is important that flexion to a right angle should not be possible. In fact, a slight degree of equinus is essential in order to secure the locking of the knee in extension, exactly as with the fixed foot (compare figures 73, 74 and 75 with figure 72), and as on the shoe there is always a heel which makes us walk normally in slight equinus, the two feet will be similar in appearance, the slight movement of the artificial foot being sufficient to allow a rolling movement of the sole upon the ground (Figs. 77 to 86).

The figures 76 and 76A show the simplest and best known mechanism. On the upper surface of the foot two cavities are hollowed, one in front and one behind the bolt of the ankle joint, in each of these is placed a cylinder of rubber; the posterior cylinder is about twice as thick as the anterior. Above them the leg piece is fixed, it ends in front in a short instep which lies within the cavity hollowed out in the foot.

The foot is attached to the leg piece by a bolt made as follows: a steel tube fitting into two corresponding grooves in the leg and foot, is attached to the leg by being prolonged upward into a vertical rod, which is secured by a nut inside the leg piece.

Upon the steel tube moves a brass rod shaped like an inverted U, the two ends of which pass through the foot and fasten beneath it by two nuts (Fig. 82).

Raising the point of the foot further compresses the anterior piece of rubber, lowering it relieves the pressure upon this piece and compresses the posterior piece. But the tension and the size of the pieces of rubber are such that they are under slight compression in the position of rest, the foot being in 30° of equinus. So that this foot is never loose. When pressure is made on the point of the foot it may come to within 15° or 20° of a right angle, but it returns to its angle of 30° as soon as the pressure ceases.

Contact of the sole with the ground in normal walking. Heel first then toe, with progressive dorsiflexion of the ankle joint. Compare with the contact of the artificial foot in figures 82 to 86.]

With boots on, with heels of 2·5 centimetres the two feet are in the same position when the soles are flat on the ground.

The forepart of the foot (representing the toes and the anterior part of the metatarsals) is kept in this position (Fig. 76) in slight extension by a piece of rubber, compression of which allows an increase of extension of 15° to 20°.

When a step is taken, the heel of the foot first meets the ground, the leg pointing downwards and forwards. Then the whole sole comes to lie flat on the ground, the degree of equinus being increased, the posterior rubber compressed and the anterior relaxed (Figs. 82 and 83), but when the limb is vertical the sole still being flat on the ground, compression of the posterior diminishes and that on the anterior increases (Fig. 84). This remains unchanged up to the moment when the foot leaves the ground, whilst the heel rises and the weight is borne on the toe piece of the foot, which is forced into extension (Figs. 85 and 86).

FIG. 83.