Among the theories suggested in explanation of these arthropathies the most recent is that by Babinski and Barre, which traces the condition to vascular lesions of a syphilitic type in the articular arteries.

The first symptom is usually a swelling of the joint and its vicinity.  There is no redness or heat and no pain on movement.  The peri-articular swelling, unlike ordinary oedema, scarcely pits even on firm pressure.

[Illustration:  FIG. 162.—­Bones of Knee-joint in advanced stage of Charcot’s Disease.  The medial part of the head of the tibia has disappeared.

(Anatomical Museum, University of Edinburgh).]

In mild cases this condition of affairs may persist for months; in severe cases destructive changes ensue with remarkable rapidity.  The joint becomes enormously swollen, loses its normal contour, and the ends of the bones become irregularly deformed (Fig. 162).  Sometimes, and especially in the knee, the clinical features are those of an enormous hydrops with fibrinous and other loose bodies and hypertrophied fringes—­and great oedema of the peri-articular tissues (Fig. 163).  The joint is wobbly or flail-like from stretching and destruction of the controlling ligaments, and is devoid of sensation.  In other cases, wearing down and total disappearance of the ends of the bones is the prominent feature, attended with flail-like movements and with coarse grating.  Dislocation is observed chiefly at the hip, and is rather a gross displacement with unnatural mobility than a typical dislocation, and it is usually possible to move the bones freely upon one another and to reduce the displacement.  A striking feature is the extensive formation of new bone in the capsular ligament and surrounding muscles.  The enormous swelling and its rapid development may suggest the growth of a malignant tumour.  The most useful factor in diagnosis is the entire absence of pain, of tenderness, and of common sensibility.  The freedom with which a tabetic patient will allow his disorganised joint to be handled requires to be seen to be appreciated.

[Illustration:  FIG. 163.—­Charcot’s Disease of Left Knee.  The joint is distended with fluid and the whole limb is oedematous.]

The rapidity of the destructive changes in certain cases of tabes, and the entire absence of joint lesions in others, would favour the view that special parts of the spinal medulla must be implicated in the former group.

In syringomyelia, joint affections (gliomatous arthropathies) are more frequent than in tabes, and they usually involve the upper extremity in correspondence with the seat of the spinal lesion, which usually affects the lower cervical and upper thoracic segments.  Except that the joint disease is seldom symmetrical, it closely resembles the arthropathy of tabes.  The completeness of the analgesia of the articular structures and of the overlying soft parts is illustrated by the fact that in one case the patient himself was in the habit of letting out the fluid from his elbow with the aid of a pair of scissors, and that in another the joint was painlessly excised without an anaesthetic.