THE KNEE-JOINT. 183 



their insertion upon the neck of the femur to the articular cartilage, forming a 

 surface partly level and partly raised into longitudinal folds called retinacula. 



The synovial membrane of the joint is reflected from the neck of the femur 

 to the inner surface of the capsule, thence to the inner surface of the cotyloid liga- 

 ment and to the pad of fat in the bottom of the acetabulurn, from which it is farther 

 prolonged as a tubular investment upon the interarticular ligament. It sometimes 

 communicates, through an opening in the anterior wall of the capsule between the 

 ilio-femoral and pubo-femoral ligaments, with a synovial bursa placed beneath the 

 tendon of the ilio-psoas muscle. 



Movements. The movements allowed at the hip-joint are flexion, extension, abduction, 

 adduction, circumduction, and rotation. Extension is limited by the anterior fibres of the 

 capsular ligament and the inner band of the ilio-femoral ligament : flexion, when the knee 

 is bent, is limited only by the contact of the thigh with the abdomen, but when the knee is 

 extended the movement is arrested earlier by the hamstring muscles. Abduction is controlled 

 by the pubo-femoral band, by the lower part of the capsule, and by the upper border of the 

 neck of the femur coming into contact with the margin of the socket formed by the cotyloid 

 ligament ; adduction by the outer band of the ilio-femoral ligament, and by the upper part 

 of the capsule. Rotation outwards is checked mainly by the outer part of the ilio-femoral 

 ligament, inwards by the ischio-capsular ligament, the hinder part of the capsule, and the 

 muscles at the back of the joint. The whole extent of the movement of rotation is less 

 than the sixth of a circle. The interarticular ligament is put upon the stretch when the 

 hip is partly flexed, and the thigh then adducted (fig. 206) or rotated out, but it is in many 

 cases so slender that it can have very little influence upon the mechanism of the joint. The 

 ilio-femoral ligament is so strong that it is but rarely broken in dislocations of the hip, and 

 advantage is taken of this circumstance in attempting to reduce the displacement by 

 manipulation. During the swinging antero-posterior movements of the femur, as in walking 

 or running, the head of the bone revolves on a horizontal axis without any tendency to 

 escape from the socket, but in the lateral movements and in rotation the articular surface of 

 the head projects beyond the margin of the acetabulum on the opposite side to that towards which 

 the movement is taking place. In the erect attitude a vertical line passing through the 

 centre of gravity of the trunk falls behind the centres of rotation in the hip-joints ; the 

 pelvis therefore tends to fall backwards by over- extension of the hip-joints, but as this 

 is prevented by the tightening of the capsule in front, the trunk is supported upon 

 the thigh-bones in great measure without muscular effort by virtue of this mechanism of the 

 joint. 



THE KNEE-JOINT. 



The articular surfaces of this complicated joint are the condyles of the femur and 

 the condylar surfaces of the tibia, with interposed fibro-cartilages, the articulating 

 surface of the patella, and the patellar surface of the femur. The action is mainly 

 that of a hinge-joint. The joint is strengthened superficially by fibrous coverings 

 derived from the surrounding tendons and aponeuroses. The ligamentous structures 

 of the joint are the following. 



The internal lateral ligament, long and flat, connects the internal tuberosity 

 of the femur with the inner part of the shaft of the tibia, on which it descends to 

 beyond the level of the tubercle : some of the deeper fibres are also inserted into the 

 internal fibro-cartilage and the margin of the inner tuberosity. The tendon of the 

 semimembranosus muscle passes to its insertion beneath the posterior border of the 

 ligament, to which it sends a few fibres ; and below the inner tuberosity the lower 

 internal articular vessels are placed between the ligament and the bone. 



The external lateral ligament is a rounded cord, which extends from the 

 external tuberosity of the femur to the head of the fibula. Its internal surface lies 

 upon the tendon of the popliteus muscle and the inferior external articular vessels. 

 The tendon of the biceps flexor cruris muscle is divided into two by this ligament, 

 and between the ligament and the tendon there is frequently a synovial bursa. 

 Farther back is another less constant band, the short external lateral ligament, which 

 springs from the external condyle of the femur in connection with the outer head of 

 the gastrocnemius, and terminates below on the styloid process of the fibula. 



