THE KNEE-JOINT. 281 



between the two longest bones, and therefore the amount of leverage which can be brought to 

 bear upon it is very considerable ; 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, back- 

 ward, inward, or outward ; or a combination of two of these dislocations may occur that is, the 

 tibia may be dislocated forward and laterally, or backward and laterally; and any of these dis- 

 locations 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 

 accompanied 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 two articular surfaces. Acute synovitis, the result of 

 traumatism or exposure to cold, is very common in the knee, on account of its superficial posi- 

 tion. 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 intern us 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, leading to tubercular arthritis. The reasons why tubercular disease of the knee 

 usually 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 bones. Syphilitic disease 

 not unfrequently attacks the knee-joint. In the hereditary form of the disease it is usually 

 symmetrical, attacking both joints, which become filled with synovial effusion, and is very 

 intractable and difficult of cure. In the tertiary form of the disease gummatous infiltration of 

 the syncvial membrane may take place. The knee is one of the joints most commonly affected 

 with osteo-arthritis, 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 they 

 are occasionally met with in the elbow, and, rarely, in some other joints. Many of them occur 

 in cases of osteo-arthritis, 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. 



Genu 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 arid 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 tibiae 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 liga- 

 ment 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 con- 

 dyle, and a consequent tendency for the tibia to become separated from the internal condyle. 

 Tr, 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 direc- 

 tion downward and inward. 



Excision of the knee-joint is most frequently required for tubercular disease of this articula- 

 tion, but. is also practised in cases of disorganization of the knee after rheumatic fever, pyaemia, 

 etc., in osteo-arthritis. and in ankylosis. It is also occasionally called for in cases of injury, gun- 

 shot or otherwise. The operation is best performed either by a horseshoe incision, starting from 

 one condyle, descending as low as the tubercle of the tibia, where it crosses the leg, and is then 

 carried upward to the other condyle ; or by a transverse incision across the patella. In this 

 latter incision the patella is either removed or sawn across, and the halves subsequently sutured 

 together. The bones having been cleared, and in those cases where the operation is performed 

 for tubercular disease all pulpy tissue having been carefully removed, the section of the femur 

 is first made. This should never include, in children, more than, at the most, two-thirds 

 of the articular surface, otherwise the epiphyseal cartilage will be involved, with disastrous results 

 as regards the growth of the limb. Afterward a thin slice should be removed from the upper 



