470 The Hip-joint 



exceeding strength. The head of the bone presses most forcibly against 

 the capsule during over-extension, but it is prevented bursting through 

 it, not only by the great thickness of that part of the capsule, but also 

 by the strap-like arrangement of the rectus femoris, psoas, iliacus, and 

 gluteus minimus, which are then tightened to the utmost over the 

 front of the joint. 



Again, the strong, overhanging roof of the acetabulum is a sure 

 check against the head of femur escaping through the upper part of 

 the joint during forced adduction. I apprehend that the thigh-bone 

 would sooner break than that this could occur. 



In abduction, however, the head of the femur partially rolls out of 

 the lower and unprotected part of the acetabulum ; and when abduction 

 is extreme, the bone escapes through the neighbouring and weak 

 part of the capsule, tearing a ragged hole in its inner aspect. The 

 ilio-femoral ligament remains entire, but the ligamentum teres is, 

 of course, torn through. The head of the bone may then remain just 

 below the acetabulum and form a dislocation into the obturator 

 foramen, the limb being stiff, a little lengthened and abducted. 



Obturator dislocation ought to be the commonest variety of dis- 

 placement ; but when the bone is in the act of escaping, or has actu- 

 ally escaped, either the direction of the violence, spasmodic muscular 

 contraction, or a rotatory movement of the thigh or- the trunk causes 

 the bone to glide on to the dorsum ilii or into the great sacro-sciatic 

 notch. 



The dislocation on to the dorsum ilii is the commoner result, the 

 smaller gluteal muscles being ploughed up, and the great trochanter 

 being rolled towards the front of iliac crest. Let the student take the 

 haunch-bone in one hand and the thigh-bone in the other and work 

 out these luxations for himself ; or, better still, let him use a moist 

 preparation of the joint with ligaments prepared, and he will thoroughly 

 understand them. He will find that in the dorsal dislocation the limb 

 must be shortened because the head now occupies a higher level. 

 That as the head has passed backwards the great trochanter is rolled 

 forwards, and, being raised, that it lies near the anterior superior iliac 

 spine. The upper end of the femur being thrust backwards, on to 

 the flat bone, its lower end must needs be advanced. Thus, the limb 

 is fixed, shortened (by two or three inches), and inverted. Fixation 

 characterises every dislocation ; a bone could hardly be as movable 

 when its end is out of its socket as it is when in it. As the patient 

 lies in bed, or attempts to stand, the flexed and inverted position of 

 the thigh carries the knee across the lower part of the sound thigh, the 

 ball of the great toe resting somewhere about the opposite ankle. But 

 it should not be thought that a man who has just dislocated his femur 

 stands up for inspection, as the sketches of some text-books might 

 suggest ! 



When the head of the bone is dislocated into tbe sciatic notch 



