Medial Compartment of the Thigh Anatomy
The medial compartment of the thigh is wedgeshaped and lies between the
anterior and posterior compartments. It contains pectineus, adductors longus,
brevis and magnus, gracilis and obturator externus. The obturator nerve and
vessels and the profunda femoris vessels, together with their perforating
branches, supply the compartment.
The muscles are arranged in three layers. The anterior layer consists of
pectineus, adductor longus and gracilis, from lateral to medial (Fig. 6.21). Deep to these, forming the intermediate
layer, is adductor brevis (Figs 6.22 & 6.23). The
posterior layer consists of obturator externus and adductor magnus (Figs 6.24
& 6.25). The proximal attachments of these muscles are to the outer surface
of the bony pelvis between the superior pubic and ischial rami. In addition,
obturator externus is attached to the obturator membrane.
The more anterior muscles have higher attachments than those of the
deeper layers (Fig. 6.26). Distally, the muscles attach to the femur, except
for gracilis (Fig. 6.79), which descends below the knee to gain the proximal
end of the subcutaneous surface of the tibia in company with sartorius and
semitendinosus. Obturator externus passes laterally below and behind the
capsule of the hip joint (Figs 6.25 & 6.70) to the
trochanteric fossa on the medial aspect of the greater trochanter. Pectineus
and adductors longus, brevis and magnus slope downwards and laterally to attach
in the region of the linea aspera, the sequence being related to the layer in
which the muscle lies (Fig. 6.27). Adductor magnus has the longest attachment,
extending from the gluteal tuberosity above to the adductor tubercle below.
All the muscles in the compartment, except obturator externus, adduct the
hip joint. During walking they stabilize the femur, while the abductors of the
hip prevent tilting of the pelvis (p. 270). In addition, pectineus and adductor
longus are medial rotators and obturator externus a lateral rotator. Pectineus
assists flexion at the hip joint and gracilis flexes and medially rotates the
knee joint.
All the muscles in the medial compartment except pectineus are innervated
by the obturator nerve. Pectineus usually has a supply from the femoral nerve
but may also be supplied by the obturator nerve, and the
ischial part of adductor magnus receives fibres from the tibial part of the
sciatic nerve.
The obturator nerve gains the compartment through the obturator canal and
promptly divides into anterior and posterior divisions (Fig. 6.23). The former
passes anterior to obturator externus, while the posterior division usually
pierces and supplies the muscle before emerging onto its surface. The two
divisions then descend, respectively, anterior and posterior to adductor
brevis. The anterior division supplies adductors longus and brevis and gracilis
(Fig. 6.22), and gives sensory branches to the hip joint and to skin on the
medial side of the thigh. The posterior division lies on and supplies adductor
magnus (Fig. 6.24) and gives sensory branches, which accompany the femoral
artery through the opening in adductor magnus to supply the knee joint. Since
the obturator nerve innervates the hip and knee joints, disease in one joint
may cause referred pain in the other. Pelvic pathology, including tumours
pressing on the obturator nerve (pp 222, 234, 235) may also cause referred pain
in the hip, knee and medial side of the thigh.
Vessels
The blood supply is derived from the profunda femoris artery and its
perforating branches, supplemented by the obturator artery and other branches
of the femoral artery. The obturator artery is small and forms an arterial
circle around the margins of the obturator membrane, supplying the proximal
parts of the muscles. An acetabular branch passes beneath the transverse acetabular
ligament and accompanies the round ligament to the head of the femur. Venae
comitantes accompanying the arteries in the compartment drain into the profunda
femoris or internal iliac veins.
