tor internus and gemelli
(diagrammatic).]

#Dislocation into the Vicinity of the Great Sciatic Notch#, or
"_dislocation below the tendon_."--This variety of backward
dislocation is less common than that on to the dorsum, although
produced in the same way. The head of the femur passes beneath the
obturator internus, and this tendon, catching on its neck, checks its
upward movement (Fig. 74).

The _clinical features_ are the same as those of the dorsal variety,
but, on the whole, are less marked.

_Differential Diagnosis._--Backward dislocation of the hip is usually
easily recognised. When dislocation below the tendon occurs in a stout
person, however, it is liable to be overlooked on account of the
difficulty of feeling the displaced bone, and of the comparatively
slight amount of deformity present. The nature of the accident, the
absence of broadening of the trochanter, and the adduction and
inversion of the limb are usually sufficient to prevent a dislocation
being mistaken for an impacted extra-capsular fracture.

#Dislocation into the Obturator Foramen# (Fig. 71).--This dislocation
is produced by great force applied from behind while the thigh is
flexed and abducted, as when a weight falls on the back of a man
stooping forward with the legs wide apart. It may also result from
violent abduction by wide separation of the thighs.

The capsule gives way at its medial and lower part, and the head of
the femur comes to rest on the surface of the external obturator
muscle, its articular surface looking forward, while the trochanter
looks backward.

_Clinical Features._--In the standing position the thigh is slightly
flexed and abducted, with the foot pointing directly forward or a
little outward. The body is bent forward to relax the ilio-psoas
muscle and the [inverted Y]-ligament, the foot is advanced and the
heel drawn up. It is not uncommon for the patient to be able to walk
after the accident, and only to seek advice some time later on account
of inability to adduct and extend the limb. There is apparent
lengthening of the limb due to tilting of the pelvis downward on the
affected side. The hip is flattened, the trochanter less prominent
than usual, and the head of the bone may sometimes be felt in its
abnormal position.

[Illustration: FIG. 74.--Dislocation into the vicinity of the
Ischiatic Notch. Note relation of neck of femur to tendons of
obturator and gemelli, "Dislocation below the tendon" (diagrammatic