(2) _Papillary or Nodular Tubercle of the Synovial Membrane._--This is a condition in which there is a fringy, papillary, or polypoidal growth from the synovial membrane. It is most often met with in adult males. The onset and progress are gradual, and the chief complaint is of stiffness and swelling which are worse after exertion. Sometimes there are symptoms of loose body, such as occasional locking of the joint, with pain and inability to extend the limb; but the locking is easily disengaged, and the movements are at once free again. The patient may give a history of several years' partial and intermittent disability, with lameness and occasional locking, although he may have been able to go about or even to continue his occupation. There is a moderate degree of effusion into the joint, and when this has subsided under rest it may be possible to feel ill-defined cords, or tufts, or nodular masses, and to grasp between the fingers those in the supra-patellar pouch. There is little wasting of muscles, and it is exceptional to have signs of disease of the articular surfaces or of cold abscess. On opening the joint, there may escape fluid and loose bodies similar to those described under hydrops, and if the finger is introduced into the cavity, the upper pouch is felt to be occupied by fringes or polypoidal processes derived from the synovial membrane. The diagnosis is to be made from arthritis deformans, and in some cases from loose body of other than tuberculous origin. (3) _Cold abscess_ or _empyema_ of the knee is a rare condition, in which the joint becomes filled with pus. It usually results from a primary tuberculosis of the synovial membrane occurring in children reduced in health and the subject of tuberculosis elsewhere. (4) _Diffuse Thickening of the Synovial Membrane--White Swelling._--So long as this form of the disease remains confined to the synovial membrane, the chief feature is that of an indolent elastic swelling in the area of the joint. The swelling tapers off above and below, so that it acquires a fusiform shape, and from the wasting of the muscles it appears greater than it really is. The range of movement is moderately restricted. At first the patient limps, keeps the knee slightly flexed, and complains of tiredness and stiffness after exertion. As the articular surfaces become affected, there is pain, which is readily excited by jarring of the limb, or by any attempt at movement; the joint is held rigid, and there may be startings at night. If untreated, flexion becomes more pronounced--it may be to a right angle--the leg and foot are everted, and, in children, the tibia may be displaced backwards (Fig. 124). The wasting of muscles continues, the part becomes hot to the touch, the swelling increases, and may show areas of softening or fluctuation from abscess formation. [Illustration: FIG. 124.--Advanced Tuberculous Disease of Knee, with backward displacement of Tibia.]