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Medial Compartment of the Thigh Anatomy


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.


Muscles
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.

Obturator 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.

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