Fracture of Patella 475 



may be connected by another which traverses the ligamentum patellae. 

 Thus the patella is thrown up and the interior of the joint thoroughly 

 exposed. If further drainage yet be desired, an incision may be 

 made through the ligamentum posticum, and a drainage-tube passed 

 through the popliteal space between the popliteal vessels on the inner 

 side, and the external popliteal nerve and the biceps on the outer side. 



If the articular abscess be not attacked it may burst through the 

 supra-patellar pouch, in which case the pus is extravasated not only 

 beneath the deep fascia but also beneath the quadriceps extensor. 

 Or, following the synovial sheath of the popliteus tendon, the 

 pus may escape into the floor of the popliteal space, and, guided 

 by the vessels, may find its way into the leg beneath the calf, or 

 upwards amongst the hamstring muscles. A favourite place for 

 articular abscess to point and break is (as the limb lies bent and 

 resting upon its outer side) along the outer edge of the patella or its 

 ligament. If it burst through the front of the lower part of the capsule 

 the pus will be extravasated over the front of either tibial tuberosity, 

 over the deep fascia, and between it and the superficial fascia of leg ; 

 thus the purulent extravasation is quite subcutaneous. 



The patella is a sesamoid bone developed in the back of the 

 tendon of the quadriceps. Many tough fibres descend over the front 

 of the bone, whilst the posterior surface, covered by cartilage, arti- 

 culates directly with the condyles of the femur, without the interven- 

 tion of a synovial fold. The small bone does not touch the tibia, 

 but it is connected with its spine (p. 473) by the ligamentum patellce, a 

 strong band which is, virtually, the tendon of insertion of the quadri- 

 ceps; behind it there is a padding of fat. When the limb is loosely 

 extended the patella is freely movable, but when the joint is flexed 

 the quadriceps and its tendon are stretched, and the bone is firmly 

 imbedded in the depths of the trochlear groove, where it acts as a 

 shield to what would otherwise be an unprotected part of the articu- 

 lation. 



Practure of the patella, which is almost invariably 

 the result of muscular violence, occurs when the knee is 

 partially bent, for then the bone is supported only across 

 its equator, on the trochlear surface of the femur. The 

 apex being firmly fixed by the strong ligament (as in 

 walking upstairs), and the quadriceps contracting with 

 great vigour, the bone is broken across, and necessarily 

 into the joint. 



When anyone wishes to break a tolerably thick stick, 

 he puts it across his knee and suddenly pulls the ends 

 backwards ; transverse fracture of patella occurs in a very 

 similar manner, except that the force acts at the upper 

 end only, the other end being fixed. In the following scheme, from 

 ' Lonsdale on Fractures,' B represents the patella supported at its 



