THE KNEE-JOINT 339 



Semimembranosus may enlarge greatly. It communicates with the knee-joint and can frequently 

 be made to disappear by pressure when the knee is flexed. Treves points out that enlargement 

 of the bursa between the Biceps tendon and the external lateral ligament causes great pain 

 because the peroneal nerve crosses the sac. 1 



From a consideration of the construction of the knee-joint it would at first sight appear to be 

 one of the least secure of any of the joints in the body. It is formed between the two longest 

 bones, and therefore the amount of leverage which can be brought to bear upon it is very con- 

 siderable; the articular surfaces are but ill adapted to each other, and the range and variety of 

 motion which it enjoys is great. All these circumstances tend to render the articulation very 

 insecure; but, nevertheless, on account of the very powerful ligaments which bind the bones 

 together, the joint is one of the strongest in the body, and dislocation from traumatism is of very 

 rare occurrence. When, on the other hand, the ligaments have been softened or destroyed 

 by disease, partial displacement is very liable to occur, and is frequently brought about by the 

 mere action of the muscles displacing the articular surfaces from each other. The tibia may 

 be dislocated in any direction from the femur forward, backward, inward, or outward; or a 

 combination of two of these dislocations may occur that is, the tibia may be dislocated for- 

 ward and laterally, or backward and laterally, and any of these dislocations may be complete 

 or incomplete. As a rule, however, the antero-posterior dislocations are complete, the lateral 

 ones incomplete. 



One or other of the semilunar cartilages may become displaced and nipped between the femur 

 and tibia. The accident is produced by a twist of the leg when the knee is flexed, and is accom- 

 panied by a sudden pain and fixation of the knee in a flexed position. The cartilage may be 

 displaced either inward or outward; that is to say, either inward toward the tibial spine, so 

 that the cartilage becomes lodged in the intercondyloid notch; or outward, so that the cartilage 

 projects beyond the margin of the articular surface. Acute synovitis, the result of traumatism 

 or exposure to cold, is very common in the knee, on account of its superficial position. When 

 distended with fluid, the swelling shows itself above and at the sides of the patella, reaching 

 about an inch or more above the trochlear surface of the femur, and extending a little higher 

 under the Vastus internus than the Vastus externus. Occasionally the swelling may extend 

 two inches or more. At the sides of the patella the swelling extends lower at the inner side 

 than it does on the outer side. The lower level of the synovia! membrane is just above the level 

 of the upper part of the head of the fibula. In the middle line it covers the upper third of the 

 ligamentum patellae, being separated from it, however, by the capsule and a pad of fat. Chronic 

 synovitis principally shows itself in the form of pulpy degeneration of the synovial membrane, 

 the result of tuberculous arthritis. The reasons why tuberculous disease of the knee so often 

 commences in the synovial membrane appear to be the complex and extensive nature of this 

 sac; the extensive vascular supply to it; and the fact that injuries are generally diffused and 

 applied to the front of the joint rather than to the ends of the bone. Syphilis not infrequently 

 attacks the knee-joint. In the hereditary form of the disease the attack is usually symmetrical 

 both joints are involved. They become filled with synovial effusion and cure is very difficult. 

 In acquired syphilis gummatous infiltration of the synovial membrane may take place. The 

 knee is one of the joints most commonly affected with osteoarthritis, and is said to be more 

 frequently the seat of this disease in women than in men. The occurrence of the so-called loose 

 cartilage is almost confined to the knee, though loose cartilages are occasionally met with in the 

 elbow, and, rarely, in some other joints. Many of them occur in cases of osteoarthritis, in which 

 calcareous or cartilaginous material is formed in one of the synovial fringes and constitutes the 

 foreign body, and may or may not become detached, in the former case only meriting the usual 

 term, "loose"' cartilage. In other cases they have their origin in the exudation of inflammatory 

 lymph, and possibly, in some rare instances, a portion of the articular cartilage or one of the 

 semilunar cartilages becomes detached and constitutes the foreign body. 



(it-nil valgum, or knock-knee, is a common deformity of childhood, in which, owing to changes 

 in and about the joint, the angle between the outer border of the tibia and femur is diminished, 

 so that as the patient stands the two internal condyles of the femora are in contact, but the two 

 internal malleoli of the tibire are more or less widely separated from each other. When, however, 

 the knees are flexed to a right angle, the two legs are practically parallel with each other. At 

 the commencement of the disease there is a yielding of the internal lateral ligament and other 

 fibrous structures on the inner side of the joint; as a result of this there is a constant undue 

 pressure of the outer tuberosity of the tibia against the outer condyle of the femur. This extra 

 pressure causes arrest of growth, and, possibly, wasting of the outer condyle, and a consequent 

 tendency for the tibia to become separated from the internal condyle. To prevent this the 

 internal condyle becomes depressed; probably, as was first pointed out by Mikulicz, by an 

 increased growth of the lower end of the diaphysis on its inner side, so that the line of the 

 epiphysis becomes oblique instead of transverse to the axis of the bone, with a direction down- 



1 Applied Anatomy. 



