THE ARTICULATIONS. 



hardly restrained in any of its ordinary movements by the eapsular ligament. In 

 the hip-joint, on the contrary, the head of the femur is closely fitted to the acetab- 

 ulum for a distance extending over nearly half a sphere, and at the margin of 

 the bony cup it is still more closely embraced by the ligamentous ring of the 

 cotyloid ligament, so that the head of the femur is held in its place by that 

 ligament even when the fibres of the capsule have been quite divided (Humphry). 

 The anterior portion of the capsule, described as the ilio-femoral or accessory 

 ligament, is the strongest of all the ligaments in the body, and is put on the stretch 

 by any attempt to extend the femur beyond a straight line with the trunk. That 

 is to say, this ligament is the chief agent in maintaining the erect position without 

 muscular fatigue, the action of the extensor muscles of the buttock being balanced 

 by the tension of the ilio-femoral and eapsular ligaments. The security of the 

 joint may be also provided for by the two bones being directly united through 

 the ligamentum teres ; but it is doubtful whether this so-called ligament can 

 have much influence upon the mechanism of the joint. Flexion of the hip-joint 

 is arrested by the soft parts of the thigh and abdomen being brought into 

 contact ; 1 extension, by the tension of the ilio-femoral ligament and front of the 

 capsule ; adduction, by the thighs coming into contact ; adduction, with flexion by 

 the outer band of the ilio-femoral ligament, the ilio-trochanteric ligament, the 

 outer part of the eapsular ligament ; abduction, by the inner band of the ilio-femoral 

 ligament and the pubo-femoral band ; rotation outward, by the outer band of the 

 ilio-femoral ligament ; and rotation inward, by the ischio-capsular ligament and 

 the hinder part of the capsule. The muscles which flex the femur on the pelvis 

 are the Psoas, Iliacus, Rectus, Sartorius, Pectineus, Adductor longus and brevis, 

 and the anterior fibres of the Gluteus medius and minimus. Extension is mainly 

 performed by the Gluteus maximus, assisted by the hamstring muscles. The 

 thigh is adducted by the" Adductor magnus, longus and brevis, the Pectineus, 

 and Gracilis, and abducted by the Gluteus maximus, medius, arid minimus. The 

 muscles which rotate the thigh inward are the anterior fibres of the Gluteus 

 medius, the Gluteus minimus, and the Tensor vaginae femoris ; while those which 

 rotate it outward are the posterior fibres of the Gluteus medius, the Pyriformis, 

 Obturator externus and internus, Gemellus superior and inferior, Quadratus femoris, 

 Psoas, Iliacus, Gluteus maximus, the three Adductors, the Pectineus, and the 

 Sartorius. 



Surface Form. A line drawn from the anterior superior spinous process of the ilium to 

 the most prominent part of the tuberosity of the ischium (Nekton's line) runs through the 

 centre of the acetabulum, and would, therefore, indicate the level of the hip-joint; or, in other 

 words, the upper border of the great trochanter, which lies on Nekton's line, is on a level with 

 the centre of the hip-joint. 



Surgical Anatomy. In dislocation of the hip " the head of the thigh-bone ma}' rest at 

 any point around its socket" (Bryant) ; but whatever position the head ultimately assumes, the 

 primary displacement is generally downward and inward, the capsule giving way at its weakest 

 that is, its lower and inner part. The situation that the head of the bone subsequently assumes 

 is determined by the degree of flexion or extension, and of outward or inward rotation of 

 the thigh at the moment of luxation, influenced, no doubt, by the ilio-femoral ligament, which 

 is not easily ruptured. When, for instance, the head is forced backward, this ligament forms a 

 fixed axis, round which the head of the bone rotates, and is thus driven on to the dorsum of the 

 ilium. The ilio-femoral ligament also influences the position of the thigh in the various disloca- 

 tions : in the dislocations backward it is tense, and produces inversion of the limb ; in the 

 dislocation on to the pubes it is rekxed, and therefore allows the external rotators to evert the 

 thigh ; while in the thyroid dislocation it is tense and produces flexion. The muscles inserted 

 into the upper part of the femur, with the exception of the Obturator internus, have very little 

 direct influence in determining the position of the bone. But Bigelow has endeavored to show 

 that the Obturator internus is the principal agent in determining whether, in the backward 

 dislocations, the head of the bone shall be ultimately lodged on the dorsum of the ilium or in 

 or near the sciatic notch. In both dislocations the head passes, in the first instance, in the 

 same direction; but, as Bigelow asserts, in the displacement on to the dorsum, the head of the 

 bone travels up behind the acetabulum, between the muscle and the pelvis ; while in the disloca- 



1 The hip-joint cannot be completely flexed, in most persons, without at the same time flexing 

 the knee, on account of the shortness of the hamstring muscles. Cleland, Journ. of Anat. and Phys., 

 No. 1, Old Series, p. 87. 



