272 THE ARTICULATIONS. 



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 cotyloid ligament, so that the head 

 of the femur is held in its place by that ligament even when the fibres of the cap- 

 sule have been quite divided (Humphry). The anterior portion of the capsule, 

 described as the ilio-femoral 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 ; for a vertical line passing 

 through the centre of gravity of the trunk falls behind the centres of rotation in 

 the hip-joints, and therefore the pelvis tends to fall backward, but is prevented by 

 the tension of the ilio-femoral and capsular ligaments. The security of the joint 

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

 mentum 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 when the 

 leg is flexed on the thigh ; and by the action of the hamstring muscles when the 

 leg is extended ; l 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 outer part of the capsu- 

 lar 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 liga- 

 ment ; 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, the Gracilis, and lower 

 part of the Gluteus maximus. and abducted by the Gluteus medius and minimus 

 and upper part of the Gluteus maximus. The muscles which rotate the thigh 

 inward are the anterior fibres of the Gluteus medius, the Gluteus minimus, and the 

 Tensor fasciae 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, 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 tnberosity 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 Nelaton'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 may 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 relaxed, 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, in front of the muscle ; while in the dislocation into the 



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. 



