Adductor Magnus

Introduction

Introduction to Adductor Magnus

The adductor magnus is the largest and deepest muscle of the medial thigh compartment. It is a complex, triangular muscle composed of two functionally distinct parts: the adductor (pubofemoral) part and the hamstring (ischiocondylar) part. The muscle is a powerful adductor of the hip joint, but its dual origin and insertion also allow it to flex or extend the hip depending on which fibres are activated. The adductor magnus forms the posterior wall of the adductor canal and contains the adductor hiatus, a critical anatomical opening through which the femoral vessels pass to become the popliteal vessels. Its dual innervation from the obturator nerve and the tibial division of the sciatic nerve makes it unique and clinically important in localising nerve lesions.

Study

1. Origin and Insertion – Adductor (Pubofemoral) Part

The adductor part arises from the outer surface of the inferior pubic ramus and the ischial ramus, as well as the adjacent part of the ischial tuberosity. Its fibres pass laterally and distally, inserting along the length of the linea aspera of the femur, from the gluteal tuberosity above to the upper part of the medial supracondylar line. These fibres are arranged in a layered, fan-like manner, with the most proximal fibres inserting highest on the linea aspera.

2. Origin and Insertion – Hamstring (Ischiocondylar) Part

The hamstring part originates from the inferolateral aspect of the ischial tuberosity, sharing this origin with the hamstring muscles. Its fibres descend almost vertically to insert by a strong, rounded tendon onto the adductor tubercle of the medial femoral condyle. This tendon is easily palpable in the distal thigh. The hamstring part lies posterior to the adductor part.

3. The Adductor Hiatus

The adductor hiatus is a gap in the tendinous insertion of the adductor magnus, located just proximal to the adductor tubercle. It is bounded by the central tendon of the muscle and the femur. The femoral artery and vein pass through this opening to exit the adductor canal and enter the popliteal fossa, where they become the popliteal artery and vein. The saphenous nerve also exits the canal through a separate opening in the subsartorial fascia.

4. Relations

Anteriorly, the adductor magnus is related to the adductor brevis and longus, the profunda femoris artery and vein, and the obturator nerve. The adductor canal lies on its anteromedial surface. Posteriorly, it is covered by the hamstring muscles (semitendinosus, semimembranosus, biceps femoris) and the sciatic nerve. Medially, it is related to the gracilis and sartorius. The deep femoral vessels and their perforating branches pierce the adductor magnus to reach the posterior compartment.

5. Nerve Supply

The adductor part is innervated by the posterior division of the obturator nerve (L2, L3, L4). The hamstring part is innervated by the tibial division of the sciatic nerve (L4, L5, S1). This dual innervation reflects the hybrid nature of the muscle and provides a clinical means to differentiate between proximal obturator nerve lesions and more distal sciatic nerve injuries.

6. Blood Supply

The adductor magnus receives its arterial supply from the obturator artery, the medial circumflex femoral artery, and multiple perforating branches of the profunda femoris artery. These perforating branches pierce the muscle to supply the posterior compartment. The venous drainage corresponds to the arteries.

7. Actions

The adductor part adducts and flexes the hip joint. The hamstring part adducts and extends the hip joint. Together, they powerfully adduct the thigh against resistance, as in gripping a saddle. In the stance phase of gait, the adductor magnus helps stabilise the hip.

8. Clinical Relevance

Adductor magnus strains ('rider's strain') are common in equestrian athletes and soccer players. The adductor hiatus is a site where the femoral artery can be compressed or injured in distal femoral fractures. The muscle's proximity to the sciatic nerve means that haematoma or abscess formation can cause nerve compression. In spastic cerebral palsy, adductor magnus spasticity contributes to a 'scissoring' gait; surgical releases or botulinum toxin injections target this muscle. The perforating branches of the profunda femoris artery, which traverse the adductor magnus, provide an essential collateral circulation around the thigh.

Summary

Summary of Adductor Magnus

The adductor magnus is the largest medial thigh muscle, composed of an adductor part (obturator nerve) and a hamstring part (sciatic nerve). It adducts and either flexes or extends the hip. It forms the adductor hiatus for the femoral vessels. The muscle is clinically important in adductor strains, nerve lesions, compartment syndrome, and as a surgical landmark.