Origin and Insertion
- Origin (O): arises from the inferior ramus of the pubis and the body/inferior part of the pubic symphysis.
- Insertion (I): muscle fibers descend vertically and transition into a tendon that attaches to the medial surface of the superior part of the tibia.
- Key features: at its insertion, the tendon of the gracilis unites with the tendons of the sartorius (m. sartorius) and semitendinosus (m. semitendinosus) muscles. Together, they form an anatomical structure known as the superficial pes anserinus (pes anserinus).
Functions
- Hip joint movements: the muscle acts primarily to adduct the thigh.
- Knee joint movements: upon contraction, it flexes the leg at the knee joint and medially (internally) rotates the flexed leg.
- Stabilization: as part of the pes anserinus tendon complex, it helps stabilize the medial side of the knee joint.
Blood Supply and Innervation
- Innervation: supplied by the anterior division of the obturator nerve — n. obturatorius (L2–L3). The obturator nerve also gives off a cutaneous branch (r. cutaneus n. obturatorii) supplying the medial aspect of the thigh.
- Blood supply: the muscle receives arterial blood from several sources:
- External pudendal artery (a. pudenda externa).
- Obturator artery (a. obturatoria).
- Deep artery of the thigh (a. profunda femoris).
Topography and Fascial Compartments
- The gracilis belongs to the medial compartment of the thigh muscles, which also includes the adductor longus and adductor magnus (m. adductor longus and m. adductor magnus).
- It is positioned most medially among the thigh muscles.
- The fascia lata, which envelops all the muscles of this region, forms a distinct, isolated fascial sheath for the m. gracilis.
- On a transverse section of the upper third of the thigh, it is classified within the medial compartment, and is also relevant to the anterior thigh and femoral triangle landmarks.
Clinical and Surgical Significance
- Surgical landmark: the prominence formed by the gracilis and adductor longus muscles on the inner thigh serves as an important landmark in operative surgery.
- Buyalsky–McWhorter surgical approach: used for pelvic organ surgery. The patient is placed supine with the hips abducted and knees flexed ("frog-leg position"). An 8–9 cm incision is made over the prominence of m. gracilis and m. adductor longus, 3–4 cm away from the femoroperineal fold. The adductor brevis is then divided, and the obturator externus is exposed and split along the inferior pubic ramus to access the retropubic/paravesical space.