Cysts of joints constitute an ill-defined group which includes ganglia formed in relation to the capsular ligament.  Cystic distension of bursae which communicate with the joint is most often met with in the region of the knee in cases of long-standing hydrops.  It was suggested by Morrant Baker that cystic swellings may result from the hernial protrusion of the synovial membrane between the stretched fibres of the capsular ligament, and the name “Baker’s cysts” has been applied to these.

In the majority of cases, cysts in relation to joints give rise to little inconvenience and may be left alone.  If interfered with at all, they should be excised.

LOOSE BODIES

It is convenient to describe the varieties of loose bodies under two heads:  those composed of fibrin, and those composed of organised connective tissue.

#Fibrinous Loose Bodies# (Corpora oryzoidea).—­These are homogeneous or concentrically laminated masses of fibrin, sometimes resembling rice grains, melon seeds, or adhesive wafers, sometimes quite irregular in shape.  Usually they are present in large numbers, but sometimes there is only one, and it may attain considerable dimensions.  They are not peculiar to joints, for they are met with in tendon sheaths and bursae, and their origin from synovial membrane may be accepted as proved.  They occur in tuberculosis, arthritis deformans, and in Charcot’s disease, and their presence is almost invariably associated with an effusion of fluid into the joint.  While they may result from the coagulation of fibrin-forming elements in the exudate, their occurrence in tuberculous hydrops would appear to be the result of coagulation necrosis, or of fibrinous degeneration of the surface layer of the diseased synovial membrane.  However formed, their shape is the result of mechanical influences, and especially of the movement of the joint.

Clinically, loose bodies composed of fibrin constitute an unimportant addition to the features of the disease with which they are associated.  They never give rise to the classical symptoms associated with impaction of a loose body between the articular surfaces.  Their presence may be recognised, especially in the knee, by the crepitating sensation imparted to the fingers of the hand grasping the joint while it is flexed and extended by the patient.

The treatment is directed towards the disease underlying the hydrops.  If it is desired to empty the joint, this is best done by open incision.

[Illustration:  FIG. 166.—­Radiogram of Multiple Loose Bodies in Knee-joint and Semi-membranosus Bursa in a man aet. 38.

(Mr. J. W. Dowden’s case.)]

#Bodies composed of Organised Connective Tissue.#—­These are comparatively common in joints that are already the seat of some chronic disease, such as arthritis deformans, Charcot’s arthropathy, or synovial tuberculosis.  They take origin almost exclusively from an erratic overgrowth of the fringes of the synovial membrane, and may consist entirely of fat, the arborescent lipoma (Fig. 159) being the most pronounced example of this variety.  Fibrous tissue or cartilage may form in one or more of the fatty fringes and give rise to hard nodular masses, which may attain a considerable size, and in course of time may undergo ossification.