146 CLINICAL APPLIED ANATOMY. 



thickened and furrowed in those who kneel, and it requires a 

 considerable amount of care to render it thoroughly aseptic. 

 The second is that when the bursa is very much enlarged it may 

 laterally overlap the capsule of the knee-joint, and dissection on 

 the deep surface of the sac must be carried out with due caution 

 not to open the joint cavity. 



Owing also to the exposed position of this pre-patellar bursa, 

 it is liable to be the site of punctured wounds, such as from 

 needles, which may carry infection into the sac. An acute septic 

 bursitis results. This may also follow infection by the blood 

 stream. Pus within the sac of the pre-patellar bursa will be 

 prevented from finding its way through the overlying skin owing 

 to its denseness. Nor will it be able, fortunately, to pass easily 

 into the cavity of the knee-joint because of the resistance of the 

 capsule. It will, therefore, when it transgresses the wall of the 

 sac, become extravasated as it were into the loose subcutaneous 

 cellular tissue about the joint. Sometimes this condition has 

 been mistaken for septic arthritis, but the fact that the patella is 

 buried in the inflammatory material instead of being prominent, 

 and riding on the surface of the fluid, should easily lead to a 

 correct diagnosis. Free evacuation of the pus is necessary, 

 otherwise the overlying skin may slough, being to a great extent 

 cut off from its blood supply. 



Post-ligamental bursa. This bursa lies between the posterior 

 aspect of the patellar ligament and the front of, the upper part 

 of the head of the tibia. It may be sometimes enlarged from 

 the irritation produced by repeatedly using the knee to fix a 

 piece of wood against a carpenter's bench. The bursa does not 

 communicate with the knee-joint, but in spite of this fact dis- 

 tension may simulate a collection of fluid within the joint. The 

 swelling, however, caused by the bursa only obliterates the lower 

 natural depressions, namely, those on either side of the liga- 

 mentum patellae and not those seen laterally above the patella, all 

 four of which concavities are lost in synovitis of the knee-joint. 



Semi-membranosus bursa. This sac is a so-called bursa situated 

 between the tendon of the semi-membranosus and the inner head 



