Of all deviations from the healthy condition of Joints, the diseases of texture are the most serious, both on account of their frequency, of their relations to other diseases, and of the varieties which they present in their earlier stages, according to the particular structure that was affected first, among the many of which the compound apparatus of joints is composed. Moreover, they very often lead to alterations in the relative position of the bones, and in the form of the joints.

1. Deficiency And Excess Of Development

Just as, when one or more bones are wanting, there is a deficiency of the corresponding joints, so in the opposite case, supernumerary bones are articulated to the skeleton by additional joints. But sometimes joints are really absent; or, when the bones which should compose them are incompletely developed, a mere indication only of the articular structures exists. The osseous framework is partially developed and rudimentary; the capsule of the joint is very small; and when the bones fail much of their complete development, though the stump which represents their articular extremity be covered with cartilage, the capsule is detached, and the ligaments are partly or altogether wanting. The joints by which supernumerary bones are attached are very commonly defective; and in congenital anchylosis the articular apparatus is entirely absent.

On the contrary, supernumerary joints are met with, not only when there are more bones than usual, but when their number is natural. Not an unfrequent example of the latter fact is shown in the connection of adjoining ribs together by means of an articulation.

2. Deviations Of Form

These deviations are extremely numerous and very varied in their character: sometimes they are congenital, and are caused by some fault of original formation; at other times, and far more frequently, they are secondary, and occur either before or after birth, as consequences of permanent dislocation of the bony structures of the joints, or of disease of their texture.

The cases of the former, or congenital, class may in general be reduced to unnaturally large or small size of the heads, or prominences in joints, on the one hand, and to increased or diminished capacity of the fossae on the other. And the shape of articulations may be altered in various ways by the shortness or unnatural position of articular processes, or by peculiarities in their attachment to the shaft of the bone; a fact of which the import has been shown in the instance of the neck of the femur.

The deformities of joints which are acquired after birth, are much more numerous and more important: they consist, in general, of some uneven enlargement, flattening, or diminution, or of complete destruction of the head of an articulation; of dilatation, narrowing, or wasting of articular cavities; of bending of bones, and their articular processes, etc.

3. Alterations In The Contiguity Of The Structures Of Joints

The chief of these anomalies are dislocation and anchylosis.

Dislocation consists in the slipping of the portions of bones which compose a joint over one another, so that they enter into new relations of contiguity. It is evident that there may be many degrees of it; and hence a distinction is drawn between complete luxation and incomplete, according as the articular surfaces are entirely separated, or still remain in some contact with each other.

There is a difference, too, between luxation from violence and spontaneous luxation, which occurs in the course, and is a consequence, of inflammation and ulcerative destruction of joints, but yet, as will appear, is a consecutive, and not an essential, phenomenon of the disease. The former is a result of violent injury to a joint, or of transient or persisting immoderate muscular action, and it occurs most frequently in joints which have freedom of motion. The greater the displacement, so much the more is it complicated with stretching, or rupture of the ligaments of the joint, and even with laceration of muscles, vessels, etc. Rupture of the ligaments most commonly occurs in the dislocation of joints which have limited motion. Unnatural width or shallowness of the cavities of joints, and too great length and laxity of their ligaments, predispose of course to dislocation, and to the occurrence of it upon slight occasions. The facility with which dislocation occurs in some individuals, and their ability to produce it at will (habitual dislocation), depend upon the same physical condition.

Spontaneous luxation is usually the result of destruction of the bony parts of a joint, and of the reaction of the surrounding muscles which takes places in the course of the disease: the extent of displacement corresponds with the amount of destruction which has occurred. A further account of this condition will be more conveniently given below.

Lastly, luxation may be either congenital or acquired. Congenital luxation has been only lately recognized: it has been observed in several joints, chiefly in the hip. Guerin regards it as probably the consequence of muscular retraction in the foetus, just like club-foot, "which is essentially a dislocation. Various other dislocations may, like club-foot, be produced at later periods of life by muscular retraction. Congenital luxation, when examined in a grown-up person, does not present such striking characters that it can be distinguished with certainty from a dislocation which occurred in early childhood, or even from one produced by muscular action before the bones were completely formed. It appears to me to require a thorough examination of the patient in order to determine any particular luxation to have been congenital; for, in the hip-joint more particularly, the changes which are produced by coxalgia bear a deceptive resemblance to congenital luxation, and many cases of that disease have, in the preparation, been looked upon as congenital dislocation.

Luxation is followed by some more remote changes in the joint. The capsule becomes enlarged, and the place of its insertion altered; the articular cavities of the bones increase in size, and undergo various changes in form; and corresponding alterations are produced in the articular heads or prominences. In other cases, in which the dislocation is complete, the capsule wastes, and the bony cavities diminish in size, or are filled with masses of new osseous substance; the displaced head of the bone loses its character, and a new joint is formed. The cellular structures which surround the dislocated head inflame, and frame a new capsule around it, which, for the most part, fits closely, is of fibroid structure, and has a serous lining; whilst the pressure of the head in its new position occasions a shallow articular excavation beneath it. In other cases, instead of an excavation beneath the head, a mass of callus springs up around it, and forms either a hollow to receive it, or a level surface, which the head may be flattened in order to fit; or, lastly, the callus may project, and that which was the articular head be excavated to receive it. Sometimes the quantity of new bone deposited around a dislocated head is very abundant, and retains it firmly in its place.

In dislocations of long standing, the pressure upon the vessels and nerves interferes with the nutrition of the luxated bone, and, like the soft parts, it is found in a state of atrophy.

Of anchylosis (stiffness of a joint) there are many degrees. In the highest the joint is fixed by means of bone, - two bones which were connected by articulation, unite into one - synostosis. In slighter degrees the synovial membrane wastes, the cavity of the joint is obliterated, the articular extremities of the bones become bound together by means of a fibroid or cellular tissue, and the joint is still capable of some motion. These constitute true anchylosis, and must be distinguished from the stiffness of a joint which is produced by swelling, shrinking, and tightness of the fibrous ligaments, or of the fasciae which surround a joint, or that which arises from a contracted state of the muscles, etc. To such the name of false anchylosis is commonly applied.

Anchylosis is, in most cases, the consequence of well-marked inflammation of a joint, and frequently occurs, therefore, after injuries in its neighborhood, or when caries or necrosis encroaches upon it. But it comes on also without causes of this kind in joints which have long been unused; especially in contracted joints, the articular surfaces of which have remained for a long time in close contact with one another; and in old age, in which the diminished secretion of synovia probably gives the first occasion to structural disease, and ulceration of the cartilages of the joint.

In bony anchylosis the articular ends are either bound together by flattened or rounded bridge-like growths of bone which frequently follow the course of the fibrous ligaments; or they are so united in their whole thickness, that the two or more bones which composed the joint now form but one. Sometimes, on making a section of an anchylosed joint, in which there has been no previous loss of substance in the bone, a streak is seen which represents the compact articular surface; but if that have been destroyed by suppuration, the spongy substance of one bone is uninterruptedly continuous with that of the other.

Anchylosis is sometimes confined to a single joint, sometimes it exists in several: a few cases have been observed in which nearly all the joints were anchylosed, and most of the synchondroses also.

The joints in which anchylosis most frequently occurs are the hip, the elbow, and the knee; next in order to them are the joints of the foot and hand, then the shoulder, and the articulation of the atlas and occiput, whilst that of the lower jaw, and the sterno-clavicular, and acromial joints are very rarely affected.

4. Solutions Of Continuity

To this class belong fractures of bone within the capsule of a joint, lacerations of the capsule and ligaments, disruption of the interarticular cartilages, of the cartilaginous coverings of a joint, etc, and all of them are results of violence.