4^4 The Knee-joint 



As a matter of fact, however, the limb has to be straight ; for when it is 

 flexed the patella is tightly dragged down below the condyles and the 

 quadriceps is so tense that it is impossible to work beneath it. The 

 cushion of fat behind the ligamentum patellae is made very apparent 

 when the knee is extended ; it is apt to be mistaken for abscess when 

 attention is directed to it in the case of knee-disease, so soft and 

 'fluctuating' does it seem to be. 



The outline of the membrane may be traced upon the skin by 

 making a crescentic mark across the thigh, convex upwards, three inches 

 above the patella, with its horns descending in front of the femoral 

 tuberosities, and by then making a transverse line just above the apex 

 of the patella. The latter mark shows the lower limit of the membrane, 

 which does not cover the patella in its whole extent, but slopes from 

 it down to the front of the tibial head. The line is then to be kept close 

 along the top of the tibia and to skirt the femoral condyles below 

 the tuberosities (to which the lateral ligaments are attached). Having 

 crept through to the back of the articulation, the membrane ascends to 

 line the posterior ligament, and to cover the back of the condyles. 



Synovitis causes effusion into the joint, and if the effusion be 

 rapid, the sensory nerves are suddenly stretched, great pain resulting. 

 The tension of the capsule is then extreme. But if the effusion be 

 gradual, as happens in chronic synovitis, there may be little pain, even 

 though the joint contain several ounces of fluid, and bulge high above 

 the patella, as the stretching of the nerves is slow and easy. At the 

 sides, where the lateral ligaments strengthen the capsule and prevent 

 it yielding, there is no bulging. Fluid collecting between the trochlear 

 surface and the patella floats the patella off that surface, and the knee 

 is slightly bent, as in that position there is more room for the fluid in 

 the articulation. 



In effusion into the joint the fluid is obviously behind the patella, 

 whilst in effusion into the bursa patellae the fluid is in front of the bone, 

 obscuring, or even hiding, it. 



When the knee is distended with fluid there is a bulging above 

 and at the sides of the knee-cap, under the quadriceps, and on either 

 side of the ligamentum patellae. As the patella is actually in the sub- 

 stance of the capsule, when the latter becomes distended the knee-cap 

 is carried forward or 'floated' from the trochlear surface, which it can 

 be made to touch by being thrust back through the fluid. By grasping 

 the front of the lower part of the thigh with the flat of the hand and 

 laying the fingers and thumb along the sides of the knee-cap, the fluid 

 may be made to bulge even if only small in quantity on either side 

 of the ligament ; and from this region it may be driven by pressure 

 with the other hand up again to the supra-patellar pouch, with a de- 

 finite fluctuation beneath the patella. 



To open an abscess in the joint, a bold incision on one side, or on 

 both sides of the patella should be made ; if necessary, the incisions 



