Pectineus – Origin, Insertion, Nerve Supply, Function

 Pectineus muscle is a flat, quadrangular muscle, situated at the anterior (front) part of the upper and medial (inner) aspect of the thigh. The pectineus muscle is the most anterior adductor of the hip. The muscle does adduct and laterally rotate the thigh but its primary function is hip flexion. It can be classified in the medial compartment of the thigh^[rx] (when the function is emphasized) or the anterior compartment of thigh (when the nerve is emphasized).^[rx]

Origin of Pectineus

• The pectineus muscle origin –  from the pectineal line of the pubis and to a slight extent from the surface of the bone in front of it, between the iliopectineal eminence and pubic tubercle, and from the fascia covering the anterior surface of the muscle; the fibers pass downward, backward, and lateral, to be inserted into the pectineal line of the femur which leads from the lesser trochanter to the linea aspera.
• Pectineus muscle inserts – into the posterior surface of the femur, along the pectineal line and proximal part of linea aspera. These two aforementioned lines are continuous with each other; the pectineal line continues inferiorly from the intertrochanteric line and ends by fusing with the spiral line of the femur, thus forming the medial lip of linea aspera.

Nerve Supply

• The lumbar plexus is formed from the anterior rami of nerves L1 to L4 and some fibers from T12. With only five roots and two divisions, it is less complex than the brachial plexus and gives rise to a number of nerves including the femoral nerve and accessory obturator nerve.
• The pectineus muscle is considered a composite muscle as the innervation is by the femoral nerve (L2 and L3) and occasionally (20% of the population) a branch of the obturator nerve called the accessory obturator nerve.
• When it is present, the accessory obturator nerve innervates a portion of the pectineus muscle, entering the muscle on its dorsomedial aspect. 

Blood Supply

• The superficial part of the muscle is supplied by the medial circumflex femoral artery, a branch of the femoral artery.
• A deep portion of the muscle is vascularised by the anterior branch of the obturator artery, itself a branch of the internal iliac artery.

Function

• It is one of the muscles primarily responsible for hip flexion. It also adducts the thigh.
• Due to the course of its fibers, pectineus both flexes and adducts the thigh at the hip joint when it contracts. When the lower limb is in the anatomical position, contraction of the muscle first causes flexion to occur at the hip joint. This flexion can go as far as the thigh is at a 45-degree angle to the hip joint.
• At that point, the angulation of the fibers is such that the contracted muscle fibers now pull the thigh towards the midline, producing thigh adduction. An example of a sequential movement that involves both actions of pectineus muscle is crossing your legs at the knee or ankle. Hip flexion solely is an action that, in synergy with the psoas major, iliacus, rectus femoris, and sartorius, enables the carry-through phase of the gait cycle.

References

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