342 THE AETICULATIOJSTS OE JOINTS. 



in the anterior wall of the capsule (Fig. 316), situated between the pubo-capsular 

 ligament and the medial or lower limb of the ilio-femoral ligament. 



Movements at the Hip-Joint. The movements which occur at the hip-joint are those of 

 a multiaxial joint. These are flexion, extension, abduction, adduction, rotation, and circumduction. 

 The range of each of these movements is less extensive than in the case of the shoulder-joint, be- 

 cause, at the hip, the freedom of movement is subordinated to that stability which is essential alike 

 for the maintenance of the erect attitude and for locomotion. When standing at rest in the erect 

 attitude the hip-joint occupies the position of extension, and as the weight of the trunk is trans- 

 mitted in a perpendicular which falls behind the centres of the hip-joints, both the erect attitude 

 and the extended position are maintained to a large extent mechanically, by means of the tension 

 of the ilio-femoral ligament, without sustained muscular action. Moreover, the tension of this 

 ligament is sustained by the pressure of the front of the head and neck of the femur against its 

 synovial surface. In this association of parts it is important to note that the articular cartilage 

 of the femoral head may be, and in certain races is, prolonged to the front of the femoral neck ; 

 and further, that the constant friction does not destroy the synovial stratum of the capsule. 

 Again, the same mechanism which preserves the erect attitude prevents an excessive degree oi 

 extension or dorsiflexion. In movement forwards, i.e. ventral flexion, the front of the thigh 

 is approximated to the anterior abdominal wall. The amount of this movement depends upon 

 the position of the knee-joint, because when the latter is flexed the thigh may be brought into 

 contact with the abdominal wall, whereas when the knee-joint is straightened (i.e. extended) 

 the tension of the hamstring muscles greatly restricts the amount of flexion at the hip-joint 

 Abduction and adduction are likewise much more restricted than at the shoulder-joint. Abduc- 

 tion is brought to a close by the tension of the pubo-capsular band and the lower part of the 

 capsule, and, in addition, the upper aspect of the neck of the femur locks against the margin 

 of the acetabulum. Excessive adduction is prevented by the tension of the upper band of the 

 ilio-femoral ligament and the upper part of the capsule. Rotation or movement in a longi- 

 tudinal axis may be either medially, i.e. towards the front, or laterally, i.e. toward the back. 

 In the former the movement is- brought to a close by the tension of the ischio-capsular ligament 

 and posterior part of the capsule, aided by the muscles on the back of the joint ; in the latter 

 rotation laterally the chief restraining factor is the lateral or upper limb of the ilio-femoral 

 ligament. The total amount of rotation is probably less than 60. 



Circumduction is only slightly less free than at the shoulder, but it is complicated by the 

 preservation of the balance upon one foot. 



The value and influence of the ligamentum teres femoris are not easily estimated, because it 

 may be absent without causing a"ny known interference with the usefulness of the joint. In the 

 erect attitude this ligament lies lax between the lower part of the femoral head and the acetabular 

 fat. In the act of walking it is rendered tense at the moment when the pelvis is balanced on the 

 summit of the supporting femur. Analysis of this position shows the femur to be adducted, 

 with probably, in addition, a small amount of flexion (i.e. bending forwards) and medial 

 rotation. Again, this ligament is said to be tense when the thigh is rotated laterally. The 

 equivalent of this movement is doubtless found in the rotation of the pelvis, which occurs in 

 the act of walking at the moment of transition from the toe of the supporting foot to the heel of 

 the advancing foot. The interest connected with this ligament is perhaps rather morphological 

 than physiological. It is believed by some to represent the tendon of a muscle which in birds 

 occupies a position external to the joint capsule. 



ARTICULATIO GENU. 



The knee-joint is the largest articulation in the body, and its structure ie 

 of a very elaborate nature. The part it plays in maintaining the erect attitude 

 materially influences its construction, and special arrangements are provided for thei 

 mechanical retention of the joint in the extended position in view of the fact thaij 

 the line of gravity falls in front of the centre of the articulation. Its principal 

 axis of movement is in the transverse direction, consequently it belongs to th(j 

 ginglymus or hinge variety of the diarthroses. At the same time a slight amounij 

 of rotation of the tibia in its long axis is permitted during flexion ; but while thiij 

 fact is of considerable importance in the study of certain accidents to which thi] 

 joint is liable, as well as in the study of its comparative morphology, it is no i 

 sufficiently pronounced to interfere with its classification as a hinge-joint. 



Articular surfaces pertaining to the femur, tibia, and patella enter into th<| 

 formation of the knee-joint. The articular surface of the femur extends over ti 

 large part of both condyles, and may be divided into patellar and tibial portion 

 by faintly -marked, almost transverse grooves, which pass across the articula 

 surface immediately in front of the intercondylar notch. As a rule marginal 

 indentations of the articular surface render the positions of these transvers 

 grooves more distinct. 



