HYGROMA OF THE KNEE. 



65 



The hygroma is usually characterised by its non-painful character 

 and by regular fluctuation throughout. The walls of the serous bursas 

 are merely thickened, so that palpation is easy. 



Should the hygroma become infected and inflamed, it assumes the 

 same characters as an abscess : it becomes highly sensitive, is surrounded 

 by oedematous infiltration, shows more marked fluctuation at some 

 specialised point, and eventually breaks, discharging pus. 



Long-standing hygromas often have thickened fibro-cartilaginous 

 and extremely hard walls, which render 

 examination more difficult. 



Where the hygroma is much exposed 

 to friction the skin covering it undergoes 

 complete transformation, the layers of 

 epidermis becoming converted into a 

 substance resembling horn. The entire 

 substance of the wall of the hygroma then 

 undergoes change, and is often infiltrated 

 with lime salts or encrusted with plates of 

 bone of varying thickness. 



HYGROMA OF THE KNEE. 



This condition is very common in 

 bovines, a fact explained by the manner 

 in which these animals rise. Whilst the 

 hind limbs are being lifted, the entire 

 burden of the body weight is transmitted 

 to the knees and the tissues covering them ; 

 so that, if the ground is rough, the skin may 

 be sufficiently displaced to produce lacera- 

 tion of the subcutaneous connective tissue, 

 serous efl'usion in the layers of connective 

 tissue, and the immediate production of 



an hygroma beneath the skin and in front of the synovial sheaths of 

 the extensor tendons. 



Hygroma is principally caused by falls on the knees, roughness of the 

 stable floor, prolonged decubitus during the course of a serious disease, 

 or after an attack of foot-and-mouth disease. 



Hygromas may be no larger than a turkey's egg or a man's clenched 

 fist, but sometimes assume the dimensions of a child's head. Calcifica- 

 tion and ossification of the walls and cornification of the skin are 

 commonest in old hygromas of the knee. 



The sensibility and uniform fluctuation make mistakes in diagnosis 



D.C. F 



Fig. 25. — Old-standing hygroma 

 of the knee. PE, external coat; 

 CC, cornified coat ; CO, osseous 

 coat ; CP, pus cavity ; PI, internal 

 coat. 



