REGION OF THE KNEE. 



535 



Patella 



The articular surfaces of the condyles are not perfect arcs of a circle. If they were 

 the motion would be solely a gliding one and the lateral ligaments and crucial liga- 

 ments would be equally tense in all positions, which is not the case, for, particularly in 

 flexion, they become slightly relaxed. The upper surface of the tibia is slightly 

 hollow and its spine projects upward between the condyles, thus adding to the 

 lateral stability of the joint. 



The patella is divided by a longitudinal ridge into two articular facets, the outer 

 for the external condyle being the larger; the ridge lies in the intercondylar space. 

 The inner part of the" patella is 

 thicker than the outer because 

 the inner condyle is lower. The 

 patella is a sesamoid bone which 

 is developed more toward the 

 deep surface of the tendon of the 

 quadriceps. The tendon goes 

 over the surface of the patella 

 and is practically continued 

 longitudinally through the su- 

 perficial portion of the bone. If 

 the dried specimen is hammered 

 the bone can be pulverized and 

 removed, leaving the tendon of 

 the quadriceps continuous with 

 the tendo patellae. For this rea- 

 son, when the patella frac- 

 tures, the torn fibrous fringes 

 are never on the articular sur- 

 face but always on its superficial 

 surface. The patella has its 

 sharp apex below and fractures 

 frequently tear it off, the small 

 size of the fragment making 

 repair difficult. 



Ligaments of the Knee- 

 joint. To provide for the sup- 

 port required to be given by 

 the lower extremity, the liga- 

 ments and tendons binding the 

 bones of the knee together 

 are both numerous and strong. 

 The bond of union is so strong 

 that dislocations from traumatic 

 causes are comparatively rare, 

 and it is only when the ligaments 

 have been weakened by disease 

 that subluxations take place. 



The knee possesses the usual capsular ligament but so hidden by strengthening 

 bands and tendinous expansions that but little of it is seen. Anteriorly the capsule 

 is strengthened by the tendon of the quadriceps, the patella, and the tendo patellae 

 (Fig. 545). Viewing these structures as a whole we see that their lower end is firmly 

 attached at the tibial tubercle, but above their attachments are far removed from the 

 joint. They are so strong and thick that pus from within does not tend to go through 

 but goes around them. Their upper attachment is muscular, so they do not act to 

 restrain movements except when the muscle is contracted; hence flexion is limited 

 by contact of the soft parts posteriorly rather than by tension of the ligaments ante- 

 riorly. In complete extension the bulk of the patella rises above the articular sur- 

 face, and connecting its upper edge with the anterior surface of the femur is only the 

 thin capsular ligament, hence effusions into the joint bulge upward at this point. 

 Extending about 5 cm. (2 in.) above the patella is the subfemoral bursa; this in 8 out 



FIG. 545. Knee-joint distended with wax, showing the extent of its 

 cavity and capsular ligament. 



