The chronic stage is marked by the development of a new set of symptoms—contractions of certain muscles surrounding one or more joints and deformed positions of the limbs. These symptoms do not always appear. If all the muscles surrounding a joint are completely paralyzed and extensively atrophied, and if no weight is imposed on the limb by the action of a non-paralyzed upper segment, and if the paralyzed segment be so supported that its own weight does not approximate the insertion-points of muscles, and thus cause their passive retraction, then there is no deformity, but a dangling limb, a membre de Polichinelle.
Laborde states that contractions appeared at the earliest about two months after the paralysis. Seeligmüller, however, has seen pes equinus and pes calcaneus develop in four weeks. The date is partly, at least, determined by the time at which the children try to walk or otherwise to use the paralyzed limbs; and the deformities are very much more marked in the lower extremities, proportioned to the much greater weight which they are obliged to sustain.
All varieties of club-foot, and most frequently equino-varus, knock-knees, rigid flexions at the knee and hip, cyphosis, lordosis, and colossal scoliosis may develop as manifold consequences of atrophic paralysis. That subluxation of the humerus and the claw-hand may occur in the upper extremities has already been mentioned.
In Seeligmüller's 75 cases, 53, or 71 per cent., exhibited some kind of deformity. Among these, 43, or 56 per cent., were of the foot; 6 were cases of subluxated humeri; 5, easily-reducible luxation of the fingers.
The following table contains a summary of the deformities observed as a consequence of atrophic paralysis. They are distinguishable from congenital deformities dependent on altered relations of articular surfaces through defective development61 by being easily reducible. This remark especially applies to paralytic club-foot:
| Foot. | Equinus. Equino-varus (varus hardly ever alone). Calcaneus. Calcaneo-valgus. Valgus. |
| Knee. | Genu-recurvation. Genu-incurvation. Permanent flexion. |
| Hip. | Luxation. Permanent flexion. Permanent adduction. |
| Hand. | Flexion fingers or wrist (rare). Extension of wrist. Claw-hand. |
| Elbow. | No deformity (Seeligmüller). |
| Shoulder. | Subluxation humeri. |
| Trunk. | Dorsal scoliosis. Lateral incurvation lumbar region. Cyphosis. Lordosis with backward projection of shoulders. Lordosis without backward projection of shoulders. |
61 Volkmann's Handbuch, Billroth und Pitha.
Mechanism of Deformities.—From what has been said on the cases in which deformities are absent it is evident that one at least of three conditions are required for their production: the paralysis must be unequally distributed in the muscles surrounding a joint; pressure must be exerted by the weight of the body or traction by the weight of the limb; effort must be made to utilize the maimed part of the limb by means of other parts, or even by the muscles of the trunk.
The share taken by these different factors in the production of deformities has been differently estimated by different observers. The French surgeon Delpech was the first to explain the phenomenon on the theory of muscular antagonism. The same theory has been most minutely elaborated by Duchenne.62 According to it, the intact or less paralyzed muscles, in virtue of their tonus, constantly tend to draw the segment of the limb on which they act in a direction opposed to that in which it should be drawn by the paralyzed muscles. Since this action is unantagonized, its influence persists; the insertion-points of the contracting muscle being permanently approximated, the nutrition of the muscle is modified: it grows shorter (adapted atrophy). There results finally shortening and retraction of the muscles on one side of the joint, over-stretching of those on the other.