Fracture of the _ischium_ alone is rare. It results from a fall on the buttocks, the entire bone or only the tuberosity being broken. There is little or no displacement, and the diagnosis is made by external manipulation and by examination through the rectum or vagina.
A longitudinal fracture of the _sacrum_ may implicate the posterior part of the pelvic ring, as has already been mentioned. In rare cases the lower half of the bone is broken _transversely_ from a fall or blow, and the lower fragment is bent forward so that it projects into the pelvis and may press upon or tear the rectum, or the sacral nerves may be damaged, and partial paralysis of the lower limbs, bladder, or rectum result. These fractures are frequently comminuted and compound, and the soft parts may be so severely bruised and lacerated that sloughing follows. On rectal examination the lower segment of the bone can be felt, and on manipulating it pain and crepitus may be elicited.
Fracture of the _coccyx_ may be due to a direct blow, or may occur during parturition. As a result of this injury the patient may have severe pain on sitting or walking, and during defecation. The loose fragment can be palpated on rectal examination. There is considerable difficulty in keeping the fragment in position, and if it projects towards the rectum it should be removed. If the lower fragment unites at an angle so as to cause pressure on the rectum, it gives rise to the symptoms of _coccydynia_, which may call for excision.
These include the various fractures of the upper end of the femur; dislocation and sprain of the hip-joint; and contusion of the hip.
#Surgical Anatomy.#--The strength of the hip-joint depends primarily on its osseous elements--the rounded head of the femur filling the deep socket of the acetabulum, to the bottom of which it is attached through the medium of the ligamentum teres. The edge of the acetabulum is specially strong above and behind, while at its lower margin there is a gap, bridged over by the labrum glenoidale (cotyloid ligament).
In relation to fractures of the upper end of the femur, it is to be borne in mind that as the antero-posterior diameter of the neck is less than that of the shaft, and as a considerable portion of the great trochanter lies behind the junction of the neck with the shaft, the greater part of any strain put upon the upper end of the femur is borne by the neck of the bone and not by the trochanter. The head and neck of the femur are nourished chiefly by the thick, vascular periosteum, and through certain strong fibrous bands reflected from the attachment of the capsule--the retinacular or cervical ligaments of Stanley. The integrity of these ligaments plays an important part in determining union in fractures of the neck of the femur, both by keeping the fragments in position and by maintaining the blood-supply to the short fragment. Whether it be true or not that an alteration in the angle of the femoral neck takes place with advancing years, it is generally recognised that this change is of no importance in relation to fractures in this region.