#Infective bursitis# frequently follows abrasions, scratches, and wounds of the skin over the prepatellar or olecranon bursa, and in neglected cases the infection transgresses the wall of the bursa and gives rise to a spreading cellulitis.

#Traumatic or Trade Bursitis.#—­This term may be conveniently applied to those affections of bursae which result from repeated slight traumatism incident to particular occupations.  The most familiar examples of these are the enlargement of the prepatellar bursa met with in housemaids—­the “housemaid’s knee” (Fig. 113); the enlargement of the olecranon bursa—­“miner’s elbow”; and of the ischial bursa—­“weaver’s” or “tailor’s bottom” (Fig. 116).  These affections are characterised by an effusion of fluid into the sac of the bursa with thickening of its lining membrane.  While friction and pressure are the most evident factors in their production, it is probable that there is also some toxic agent concerned, otherwise these affections would be much more common than they are.  Of the countless housemaids in whom the prepatellar bursa is subjected to friction and pressure, only a small proportion become the subjects of housemaid’s knee.

Clinical Features.—­As these are best illustrated in the different varieties of prepatellar bursitis, it is convenient to take this as the type.  In a number of cases the inflammation is acute and the patient is unable to use the limb; the part is hot, swollen, and tender, and fluctuation can be detected in the bursa.  In the majority the condition is chronic, and the chief feature is the gradual accumulation of fluid constituting the bursal hydrops or hygroma.  When the affection has lasted some time, or has frequently relapsed, the wall of the bursa becomes thickened by fibrous tissue, which may be deposited irregularly, so that septa, bands, or fringes are formed, not unlike those met with in arthritis deformans.  These fringes may be detached and form loose bodies like those met with in joints; less frequently there are fibrinous bodies of the melon-seed type, sometimes moulded into circular discs like wafers.  The presence of irregular thickenings of the wall, or of loose bodies, may be recognised on palpation, especially in superficial bursae, if the sac is not tensely filled with fluid.  The thickening of the wall may take place in a uniform and concentric fashion, resulting in the formation of a fibrous tumour—­the solid bursal tumour—­a small cavity remaining in the centre which serves to distinguish it from a new growth or neoplasm.

[Illustration:  FIG. 113.—­Hydrops of Prepatellar Bursa in a housemaid.]

The treatment varies according to the variety and stage of the affection.  In recent cases the symptoms subside under rest and the application of fomentations.  Hydrops may be got rid of by blistering, by tapping, or by incision and drainage.  When the wall is thickened, the most satisfactory treatment is to excise the bursa; the overlying skin being reflected in the shape of a horse-shoe flap or being removed along with the bursa.