486.The answer is c.(Moore and Dalley, p 683.)About 85% of hip dislo-
cations occur in a posterior direction as the head of the femur slips out of
the acetabulum. This stretches the ischiofemoral ligament, which makes up
the posterior aspect of the joint capsule. Posterior displacement is also the
typical direction of force resulting from the striking of one’s knee on the
dashboard in a head-on car accident. Anterior hip displacement is unusual
since the very strong iliofemoral ligament stabilizes the joint anteriorly and
also limits hip extension. The sciatic nerve passes just posterior to the hip
joint and may be damaged when the hip is displaced posteriorly, thus com-
promising innervation to the hamstring and posterior compartment of the
leg. The obturator nerve (answer a)exits the pelvis through the obturator
foramen and into the medial compartment of the thigh, so it is notnearby.
The pudendal nerve (answer b)innervates the external genitalia, so it
would also be unaffected. The femoral nerve (answer d)exits the pelvis
under the inguinal ligament and into the anterior compartment, thus it will
be anterior to any damage in this case. The superior gluteal nerve (answer e)
exits the greater sciatic notch, but is generally cranial to a posteriorly dis-
placed head of the femur and is mobile enough that it is unlikely to be
damaged. Therefore this is the second best answer.
487.The answer is a. (Moore and Dalley, pp 642–643.)The common fibu-
lar (peroneal) nerve bifurcates into superficial and deep branches. The
deep fibular nerve innervates all muscles of the anterior compartment of
the leg. The lateral sural cutaneous (answer b)is a cutaneous branch of
the common fibular nerve. The superficial fibular nerve (answer d)
emerges from the deep fascia and descends in the lateral compartment,
where it innervates the fibularis (peroneus) longus and brevis muscles
before dividing into median dorsal cutaneous and intermediate dorsal
cutaneous nerves, which supply the distal third of the leg, dorsum of the
foot, and all the toes. The saphenous nerve [(answer c);the terminal
branch of the common femoral nerve] distributes cutaneous branches to
the anterior and medial aspects of the leg as well as to the dorsomedial
aspect of the foot. The sural nerve (answer e)follows the course of the
lesser saphenous vein and becomes the lateral sural cutaneous nerve to
supply the anterolateral aspect of the foot.
488.The answer is b.(Moore and Dalley, pp 639, 645–646.)The fibularis
(peroneus) brevis, a pronator and everter of the foot, inserts into the tubercle
Extremities and Spine Answers 599