Hip- Joint Disease 467 



Disease of hip-joint begins in the synovial membrane or bone, 

 the first result often being an acute effusion into the synovial mem- 

 brane. The joint is at once swollen, stiffened, deformed, and pain- 

 ful ; it is swollen, because effusion distends the capsule, causing it 

 even to bulge slightly into the buttock and into the base of Scarpa's 

 triangle. Thus, the psoas and the common femoral artery are 

 pushed forwards, the artery beating prominently beneath the skin ; 

 and the crease of the groin is obliterated by the general articular 

 fulness. The stiffening and deformity are caused by the great 

 intra-articular tension. Acute effusion into a joint always stiffens it. 

 This is readily shown in the case of the hip-joint by injecting fluid 

 into it from the pelvic side, when not only does the femur become 

 rigidly fixed, but it passes first into the position of slight abduction, 

 and then into that of flexion with inversion. Muscular action, as 

 explained by Hilton, has probably no direct influence on the assump- 

 tion of these positions, the limb taking them because, the joint being 

 full, more room is found for the fluid when the femur is so arranged. In 

 these positions, therefore, there is least tension of the sensory filaments 

 of the joint. It is the unyielding anterior part of the capsule which 

 determines the position of the limb. 



The pain first complained of in hip-joint disease is on the inner 

 side of the thigh, above the pateHa, in the popliteal space, or at the knee 

 that is, in the area of distribution of the terminal branches of the 

 obturator nerve (p. 358). The reason of this is not clearly understood. 

 The explanation usually given is that the obturator nerve supplies 

 the hip-joint, thigh, and knee, and that when one set of peripheral 

 fibres are irritated the trouble is referred to the area of distribution 

 of those of the other division. In a similar manner we find that, when 

 the bladder-branches of the sacral plexus are irritated by vesical 

 calculus, the painful area is at the end of the penis, where the peri- 

 pheral branches of the nerves supplying the bladder are distributed. 



As the disease advances, the fulness of the groin and buttock 

 increases, and an abscess forms which bursts through the thin, posterior 

 part of the capsule. 



The pus may then find its way under the gluteal muscles to below 

 the great trochanter, round by the obturator externus to the inner 

 part of Scarpa's triangle, beneath the great gluteus and into the upper 

 and back part of the thigh, or through the floor of the acetabulum and 

 into the pelvis. This last is by no means an uncommon event, and in 

 examining an old case of hip disease the surgeon must not fail to pass 

 his finger into the rectum so as to make a full exploration on the inner 

 surface of the os innominatum. The pus is not in actual contact with 

 the wall of the rectum, though it is felt by the finger (v. p. 363) close 

 to it ; it is separated by the periosteum of the os innominatum, the ob- 

 turator internus and obturator fascia, and the levator ani and its fasciae. 

 It is quite possible, however, that the pus may by pressure effect a 



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