THE HIP- JOINT 



283 



It results from the obliquity of the neck of the femur that the movements of the head in 

 the acetabulum are always more or less of a rotatory character. This is more especially the case 

 during flexion and extension, and two results follow from it. First, the bearing surfaces of the 

 femur and acetabulum preserve their apposition to each other, so that the amount of articular 

 surface of the head in the acetabulum does not sensibly diminish pari passu with the transit of 

 the joint from the extended to the flexed position, as would necessarily be the case if the move- 

 ment of the femoral head, like that of the thigh itseK, was simply angular, instead of rotatory 

 and angular. Secondly, as rotation of the head can continue until the ligaments are tight with- 

 out being checked by contact of the neck of the thigh bone with the rim of the acetabulum, 

 flexion of the thigh so far as the joint is concerned is practically unlimited. Flexion is the most 

 important, most frequent, and most extensive movement, and in the dissected hmb, before the 

 ligaments are disturbed, can be carried to 160°, and is then checked by the lower fibres of the 

 ischio-capsular ligament. In the living subject simple flexion can continue until checked by the 

 contact of the soft parts at the groin, if the knee be bent; if the knee be straight, flexion of the 

 hip is checked in most persons by the hamstring muscles at nearly a right angle. This is very 

 evident on trying to touch the ground with the fingers without bending the knees, the chief strain 

 being felt at the popliteal space. This is due to the shortness of the^^hamstrings. Extension 

 is limited by the ilio-femoral ligament. 



Fig. 314. — ^Ligamentum Teres, vert l.\x in Complete Extension. 



Abduction and lateral rotation can be performed freelj' in every position of flexion and 

 extension — abduction being limited by the pubo-capsular ligament; lateral rotation by the 

 ilio-femoral ligament, especially its medial portion, during extension; but by the lateral portion, 

 as well as by the ligamentum teres, during flexion. 



Adduction is verj' limited in the extended thigh on account of the contact with the opposite 

 limb. In the slightly flexed position adduction is more free than in extension, and is then limited 

 by the lateral fibres of the ilio-femoral band and the superior portion of the capsule. In flexion 

 the range is still greater, and limited by the ischio-capsular ligament, the ligamentum teres being 

 also rendered nearly tight. Medial rotation in the extended position is limited by the lower 

 fibres of the ilio-femoral ligament; and in flexion by the ischio-capsular ligament and the portion 

 of the capsule between it and the ilio-femoral band. 



The ilio-femoral band also prevents the tendency of the trunk to roU backward on the thigh 

 bones in the erect posture, and so does away with the necessity for muscular power for this pur- 

 pose; it is put on stretch in the stand-at-ease position. 



The ligamentum teres is of httle use in resisting violence or in imparting strength to the 

 joint. It assists in checking lateral rotation, and adduction during flexion. A hgament can 

 only be of use when it is tight, and it was found by trephining the bottom of the acetabulum, 

 removing the fat, and threading a piece of whipcord round the ligament, that the hgament was 

 slack in simple flexion, and very loose in complete extension, but that its most slack condition 

 was in abduction. It is tightest in flexion combined with adduction and lateral rotation and 

 almost as tight in flexion with lateral rotation alone, and in flexion with adduction alone (figs. 

 313-315). 



Muscles which act upon the hip-joint. — Flexors. — The psoas and iliacus, the rectus femoris, 

 the pectineus, the adductors, the sartorius, the tensor fascise latae, and the gluteus medius. 



