Pectineus muscle

Origin and insertion

Pectineus is a short quadrangular muscle extending from the pubis to the area just below the lesser trochanter of femur. It has the most superior attachment of all the thigh adductors, originating from the pectineal line of pubis on the superior pubic ramus. The muscle then slides over the superior margin of superior pubic ramus and courses posterolaterally down the thigh, sometimes being partially divided into a larger anterior (superficial) layer and smaller posterior (deep) layer. The layers adhere to each other but are innervated by different nerves. 

Pectineus muscle inserts into the posterior surface of 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 femur, thus forming the medial lip of linea aspera.

Relations

The muscle lies in the same plane as, and medially to, adductor longus. While laterally, it is related to the psoas major muscle and the medial circumflex femoral artery and vein. 

The anterior surface of pectineus forms the medial part of the floor of femoral triangle together with adductor longus, while the iliacus and psoas major complete the lateral side of the floor. This surface of pectineus is covered with the deep layer of fascia lata that separates it from the femoral artery, femoral vein and great saphenous vein that course through the femoral triangle. 

Posterior to pectineus are the adductor magnus, adductor brevis and obturator externus muscles, and the anterior branch of obturator nerve. Note that the fascia lata peripherally bounds the anterior and posterior thigh compartments. These two are internally separated by medial and lateral intermuscular septa that attach to the femur. Although the adductor (medial) compartment to which pectineus belongs doesn’t have its own fascial border to separate it from the anterior and posterior compartments, it is still described separately due to common function and muscular innervation of its constituents.

Innervation

Pectineus is predominately innervated by the femoral nerve (L2, L3). However, in some people pectineus may receive innervation from two separate nerves of the lumbar plexus.

This composite innervation reflects the dual compartmentalisation of pectineus into both the anterior and medial compartments of the thigh. In these cases the anterior part of the muscle sits is innervated by the femoral nerve (L2, L3), a feature of muscles of the anterior thigh. While the posterior, smaller part of the muscle is supplied by a branch of obturator nerve (L3, L4), the accessory obturator nerve.

Blood supply

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

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Function

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 being 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 psoas major, iliacus, rectus femoris and sartorius, enables the carry-through phase of the gait cycle.

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Some sources also state that the pectineus muscle contributes to external and internal rotation of the thigh. This is still heavily debated, although it is noted that the insertion of pectineus is lateral to the midline, beyond the mechanical axis of rotation of the femur, suggesting that there could be some merit to the argument.

Besides being the prime mover, this muscle is also an important stabilizer of the pelvis. In fact, it is suggested that all the muscles attaching between the pelvis and proximal femur act as adaptable ligaments of the hip joint, preserving its integrity during body movements.

Understand the anatomy and function of the muscles of the hip and thigh with our learning materials on this topic.