CHAPTER II.

DISEASES OF THE JOINTS.

=Malformations.= Cases of congenital anchylosis, the joints being absent, have been met with; also imperfectly developed joints, with a partial or total absence of the ligaments. Supernumerary joints also occur, either with the normal, or with an excessive number of bones.

=Morbid Conditions of the Synovial Membrane.= _Inflammation_ may be acute, sub-acute or chronic. It usually results from exposure to cold, especially in rheumatic or syphilitic constitutions.

There is at first a congestion and increased vascularity of the membrane, and a loss of its satiny polish; the synovia is increased in quantity, but becomes thin and serous, and at a later period, mixed with plastic material. If the disease progress, the vascularity and swelling of the membrane increase, and it becomes turgid and distended with blood and effused fluids; a thin, purulent-looking fluid, composed of granular corpuscles, floating in a serous liquid, is poured out, and disintegration, with thinning and erosion of the cartilage, ensues; or granulations are thrown out on the looser portions of the membrane, and, becoming injected with blood-vessels, form fringed membranous expansions, in contact with the ulcerating part of the cartilage.

In chronic synovitis, the swelling from the accumulated serous fluid may become so considerable as to constitute a true dropsy of the joints—_hydrarthrosis_. This same accumulation may, however, take place without any evidence of preceding inflammation.

_Pulpy Degeneration of the Synovial Membrane_ is peculiar to the articular lining membranes, nothing analogous having been found in the serous sacs. The reflected portions of the synovial membrane are first attacked, and converted into a light-brown, pulpy substance, from a quarter to a half, or even a whole inch in thickness, intersected with white membranous lines and red spots, formed by small injected vessels. The membrane of the cartilages are then invaded, ulceration in the cartilages going on at same time, till the ulcerating surfaces of the bone are exposed.

The disease almost always occurs before the middle period of life, frequently can be traced to no cause, but is occasionally the consequence of repeated attacks of inflammation. It generally occurs in the knee, but has been met with in the ankle and in a joint of the finger.

A growth of large villous processes, presenting a shaggy appearance, is sometimes observed. “They have sometimes the form of simple threads or flattened shreds, or their free extremities are split into filaments or have a club shape, or resemble melon-seeds hanging singly, or in clusters from each stalk. In many cases, the healthy texture of the articulation is not materially affected.”

=Morbid Conditions of Bursæ.= “These small synovial sacs are liable to be affected much in the same way as larger ones. They may be attacked by inflammation more or less acute or quite chronic, resulting from rheumatism, the abuse of mercury, or some other constitutional affection; or excited by violence or long-continued pressure. The effusion which takes place may, in cases of a chronic kind, be a simple synovial or serous fluid; but when the inflammation is more acute, it is either a turbid serum, with flakes of fibrinous matter floating in it, or actual pus.” The walls of an inflamed bursa sometimes become very much thickened by the organization of layers of fibrinous effusion.

In cases of long-standing inflammation, flat oval bodies, resembling melon-seeds, of a light-brown color, are not unfrequently met with. Their origin is no doubt to be traced to the coagulated lymph effused in the beginning of the disease.

In the synovial sheaths surrounding the flexor tendons of the fingers, as they pass under the annular ligament, small bodies, resembling grains of boiled rice, are also occasionally found.

The so-called _ganglions_ are small collections of fluid in bursal cavities of new formation, and occur principally on the back of the wrist and forearm. In the sheaths of the tendons of the hand, these synovial accumulations may become so excessive, as to greatly damage the usefulness of the member.

=Morbid Conditions of Cartilage.= The thickness of cartilage may be greatly increased, while the tissue becomes soft and yielding. In advanced age, the articular cartilages become considerably thinned; ossification of the cartilage occurs, sometimes gradually with advancing years, at others in connection with chronic rheumatic arthritis. In joints apparently not diseased, we sometimes find the cartilages more or less deficient at one or more points, due to pressure and consequent partial atrophy. Sometimes its place is taken by a hard, semi-transparent substance of a gray color, with an irregular granulated surface, the result of a fibrinous exudation.

The free surface of cartilages is occasionally found covered with a thin layer of lithate of soda, as the result of gout.

_Loose cartilages_ may be found in the knee and other large joints; they never contain any of the characteristic cells of cartilage, and appear to consist solely of compressed fibrillating exudation. They vary in size and number, are more or less oval and flattened, with a smooth surface, and are sometimes attached to the synovial membrane by a pedicle of varying length. In the latter case, they are invested by a serous covering. Calcareous deposits are occasionally met with in them.

=Ulceration of Cartilage= may occur as an acute or sub-acute affection. The cartilage corpuscles, instead of being of their usual form, will be found larger, rounded or oviform; and instead of two or three nucleated cells in their interior, they contain a mass of them. The cavities of the enlarged corpuscles open on the ulcerated surface, by orifices of various sizes. The texture of the ulcerating cartilage, shows no trace of vascularity. In most cases, a vascular false membrane is found in opposition to the diseased part. The membrane generally adheres with some firmness to the ulcerating surface, in other instances it is loosely applied to it; but in all cases the two surfaces are accurately moulded to each other. If a portion of the false membrane be torn slowly off, the cartilage will be found to be rough and honeycombed, and into each depression on its surface, a nipple-like projection of the vascular membrane will be seen to have penetrated.

=Chronic Rheumatic Arthritis= is very frequent in the hip, the shoulder, the knee, and the articulations of the hand. The process consists essentially, first, in an hypertrophy of the articular cartilage, generally at the margin, and principally near to the articular surface. Secondly, in the development of true osseous tissue in the hypertrophied cartilage. We will, therefore, find irregular enlargement of the articulating head of the bone; an absence of the articular cartilages, or new osseous growths surrounding their margins; and the synovial sacs presenting evidences of having been the seat of chronic inflammation.

=Scrofulous Arthritis=, or _White Swelling_, attacks primarily the articular extremities of the bones. They become very vascular and softened, so that they can be readily cut with a knife, while a characteristic transparent and afterwards a yellow, cheesy substance is deposited in their cancelli. As the disease advances, the cartilage ulcerates, and the osseous tissue gradually wastes and undergoes a true caries. Abscess forms in the joint, and finds its way by ulceration to the external surface, causing numerous and circuitous sinuses in the neighboring soft parts.

In some cases, the disease may commence in the synovial membrane, extending finally to the cartilages and ultimately to the bone.

The disease affects principally the joints of children, and rarely occurs after the age of thirty. The existence of scrofulous disease in other parts, and the deposition of the yellow, cheesy matter within the cancelli, will serve to distinguish this disease from simple caries, resulting from inflammation.

=Disease of the Spinal Column.= The joints of the vertebræ are liable to nearly the same affections as more perfectly developed articulations.

The scrofulous disease just described may attack the cancellous tissue, causing caries and the deposition of cheesy matter. The first effects are generally perceptible where the intervertebral cartilage is connected with the bone, or in the intervertebral cartilage itself, although ulceration may commence on any part of the surface, or even in the centre of the bone. In some cases, of rarer occurrence, the bodies of the vertebræ are affected with chronic inflammation, with ulceration of the intervertebral cartilages as the consequence.

If not checked, the disease proceeds to the destruction of the bodies of the vertebræ and of the intervertebral cartilages, leaving the posterior parts of the vertebræ unaffected. The necessary consequence is a curvature of the spine forward, and a projection of the spinous processes posteriorly.

Chronic inflammation of the bones sometimes extends to the membranes of the spinal cord; and when the curvature is very great, the cord may be so compressed that it cannot properly discharge its functions. Suppuration may take place at different stages of the disease, sometimes earlier, sometimes later. “The soft parts in the neighborhood of the abscess become thickened and consolidated, forming a thick capsule, in which the abscess is sometimes retained for several successive years; but from which it ultimately makes its way to the surface, presenting itself in one or another situation, according to circumstances. In the advanced stages of the disease, new bone is often deposited in irregular masses on the surface of the bodies of the neighboring vertebræ; and where recovery takes place, the carious surface of the vertebræ above, coming in contact with that of the vertebræ below, they become united with each other, at first by soft substance, afterwards by bony anchylosis.”

Where the bones are affected by scrofula, bony anchylosis does not so readily take place as where they retain their natural texture and hardness. Occasionally, portions of the ulcerated or carious bone lose their vitality, and having become detached, are found lying loose in the cavity of the abscess. The pressure of a large abscess on the surfaces of the contiguous vertebræ may cause an extensive caries far beyond the limits of the original disease.