PRACTICAL CONSIDERATIONS : THE PELVIC JOINTS. 351 



relation of the lumbo-sacral cord, the upper sacral nerves, and the obturator has 

 already been mentioned (page 347). 



The body is inclined to the sound side, so that when sitting the pressure on the 

 diseased structures may be lessened, and when standing separation of the joint sur- 

 faces may be secured by the weight of the lower limb. The length of the latter is 

 apparently increased on account of a downward rotation of the innominate bone on 

 the affected side, but measurements from the anterior spines to the malleoli will be 

 the same. Tenderness on direct pressure may be elicited just below the posterior 

 iliac spine ; on indirect pressure by squeezing the ilia together or by separating 

 them so as to put the anterior ligaments on the stretch. 



Pus may find its way backward and appear at or near the joint line. It more 

 often passes forward on account of the greater thinness of the anterior ligament. 

 It may then enter the sheath of the ilio-psoas and be conducted to the anterior surface 

 of the thigh ; it may follow the obturator vessels through the obturator canal and 

 point on the inner aspect of the thigh ; it may be guided by the sciatic nerve and 

 the lumbo-sacral cord to the region behind the greater trochanter ; it may descend 

 between the obturator fascia and the anal fascia into the ischio-rectal fossa and appear 

 at the side of the anus ; or, finally, it may ulcerate into the rectum and be dis- 

 charged per anum. 



The symphysis pubis, as the centre of the counterarch of the pelvis (page 346), 

 is subject to manifold strains and injuries ; but, as the union between the two innomi- 

 nate bones at that point is really by a strong, solid, fibro-cartilaginous band, and is 

 without a synovial cavity, and as it is greatly strengthened by the decussation of 

 the fibres of the anterior and inferior ligaments, its separation by traumatism is very 

 rare, and is in effect a fracture. 



The anterior ligament is much stronger than the posterior to resist the down- 

 ward and forward pull of the adductors and the weight of the abdominal walls and 

 viscera. Its strength accounts for the fact that fracture of the horizontal rami is 

 more common than disjunction of the symphysis "in cases in which compressing force 

 has been applied to the pelvis laterally. 



In cases of disease when the bond of union is weakened, the function of the 

 counterarch readily explains the weakness and powerlessness in standing or sitting. 



The symphysis is of great importance in its relation to obstetric mechanics and 

 measurements. The plane of greatest pelvic expansion extends from the junction of 

 the second and third sacral vertebrae posteriorly to the middle of the symphysis ; 

 the plane of least pelvic diameter from the sacro- coccygeal articulation to the lower 

 third of the symphysis. 



There is thought to be a trifling separation of the symphysis during pregnancy 

 and labor, but this is counteracted by the decussation of the aponeurotic fibres of 

 the oblique muscles at the linea alba. On account of this decussation these muscles 

 tend, when in vigorous action, as in parturition, to draw the pubic bones together. 



The symphysis, however, although comparatively unyielding, is in almost the 

 same horizontal plane with the coccyx, the most movable bone that enters into the 

 formation of the pelvis, and with the obturator foramina and the lower part of the 

 great sacro-sciatic foramina. This is in accord with the fact that in no horizontal 

 plane does the pelvis form a complete bony and unyielding ring, but everywhere the 

 resisting bony portion has opposite to it one or more soft and yielding segments, 

 as, for example, the hypogastric region of the abdomen is opposite the fixed and 

 immovable sacrum (Morris). 



In obstructed labor in which the delivery of a living child may be made possible 

 by a moderate increase in the pelvic outlet, the operation of symphysioto7ny is often 

 performed. The aponeurosis of the recti is incised, the retro-pubic structures sepa- 

 rated by a finger, and a probe-pointed bistoury passed down and made to cut for- 

 ward and upward. The incision may with advantage be made in the reverse direc- 

 tion, as the symphysis is wider at its upper than at its lower margin, and is wider 

 anteriorly than posteriorly. The subpubic ligament and the deep perineal fascia 

 should then be detached from the pubic arch close to the bone, so as to avoid tear- 

 ing the structures that penetrate the fascia — the vagina, the urethra, the dorsal vein 

 of the clitoris, and other venous channels — when the pubes are separated. 



