The elaborate transformation above described is chiefly notable in the large joints such as the knee and the ankle. In the smaller articulations of the toes and fingers, the destructive processes are more uniform, and the ruin of the joints is more complete. Cartilages and synovial membranes disappear beyond recognition, and the ends of the bones are plastered together with a mortar-like incrustation that produces complete ankylosis and immobility of the joint. In some cases the central cavity still retains some moisture, but in many in stances all the parts of the articulation, and even the adjacent tissues for a considerable distance outside of the capsule, are solidly infil trated. This may occur in cases where no dislocation nor deviation of the phalanges nor any swelling of the joints can be perceived.
The degree in which the true osseous structures behind the diar throdial cartilages escape the destruction that ruins the softer tissues is remarkable. In the vicinity of the larger joints the epiphyseal portions of tho long bones sometimes appear unchanged, though the articulations are profoundly altered by disease. Usually, however, the bone shares in the morbid process.
A certain amount of osseous swelling can be demonstrated as the result of chronic osteitis. The central spongy portion becomes more spongy and vacuolated, while the peripheral parts are condensed and eburnated by the infiltration of ordinary earthy salts.
Unlike the cartilages the bones almost never contain uratic de posits. In a few very exceptional cases which were observed by Fereol and Sir Alfred Garrod, the diarthrodial extremities had been destroyed, and certain little pockets in the bony substance were filled with a deposit that was continuous with the intra-articular incrusta tions. In only one instance did Fereol find the diaphysial portion of a single phalanx actually infiltrated with orates.
The periosteum, on the contrary, by reason of its fibrous charac ter, shares in the predisposition manifested by similar articular tis sues to become the seat of an abundant uratic deposit.
In the majority of cases, then, it appears that the osseous changes consist in a chronic inflammation that rarefies the spongy portion of the bone, and leads to an increase of fatty matter in its substance, clue to fatty degeneration of the osteoplastic cells; while the external portion of the shaft becomes ebnrnated and enlarged without uratic infiltration. Occasionally the lesions of arthritis deformans are
found coexistent with those of gout. This is especially true of the smaller joints, which are sometimes surrounded by osteophytes that have formed in the marginal structures. These growths, however, are not characteristic of gout, for they do not consist of urates, and they may be encountered in other forms of arthritis.
By the aid of the microscope the infiltrative process is made still more conspicuous. The crystalline forms of sodium urate are ren dered visible, so that the dust-like deposits and the clayey streaks and patches which seem to incrust the cartilaginous surfaces can be seen to lie beneath the serous investment. Fine lines of needle-like forms can be traced far into the substance of the cartilage, radiating usually from a central mass of crystals that looks opaque and homo geneous by reason of its condensation. It seems probable that these minute structures are at first deposited in the substance of the car tilage cells.
It is, moreover, certain that the fundamental substance of the car tilage is also occupied by the same crystalline deposit; but whether the process goes on simultaneously or successively in these two struc tures, cannot be positively determined at present.
' When the irritation excited by the nratic deposit reaches the grade of inflammatory action the nuclei of the cartilage cells multiply and revert to their embryonal state. The superficial layers thus crowded with chondroplasts of recent formation become organized by an ar rangement of cellular elements in rows parallel to the diarthrodial surface. The corresponding layers that lie contiguous to the bone allow their proliferating elements to range themselves in lines that are perpendicular to the osseous substance; while the intermediate layers lie at random without any attempt at linear order. At an early stage of the process the joint surfaces exhibit merely an absence of their normal polish, but with the progress of the disease the funda mental substance of the cartilage splits up, giving it a velvety appearance. At a still later period all the phenomena of erosive inflammation and mineral incrustation may be observed.
In the articular ligaments and synovial structures the same course of events may be studied. The process begins with a subserous de posit of mineral matter, and everything else follows as in the carti laginous structures.