Gracilis
| |
| Gracilis | |
|---|---|
| Muscle Type | |
| Origin | ischiopubic ramus |
| Insertion | tibia (pes anserinus) |
| Action | flexes, medially rotates, and adducts the hip |
| Synergists | |
| Antagonists | |
| Spinal innervation | |
| Peripheral Innervation | anterior branch of Obturator Nerve |
| Vasculature | medial circumflex femoral artery |
The gracilis muscle is a fusiform muscle located in the medial compartment of the thigh. Superiorly it is thin, flattened and broad, and tapers is it descends. It is the most superficial of the adductor muscles, and is innervated by the obturator nerve (L2-L4).
Muscle Type
Gracilis is a thin, strap-like superficial muscle in the medial (adductor) compartment of the thigh. It is the most superficial and medial of the adductor group, running vertically along the inner thigh. Gracilis is also biarticular, crossing both the hip and knee joints.
Origin
It originates from the inferior pubic ramus and the inferior margin of the pubic symphysis of the pelvis. The attachment spans the pubis and adjacent ischial ramus, near where the adductor brevis and magnus also arise.
Insertion
Gracilis inserts on the medial surface of the proximal tibia, just below the medial condyle. Specifically, it attaches to the medial aspect of the tibial shaft, just posterior to the insertion of sartorius. This insertion via a common tendon contributes to the pes anserinus (along with sartorius and semitendinosus), on the anteromedial aspect of the tibia.
Action
At the hip, gracilis adducts the thigh (brings the leg inward toward midline). At the knee, it assists in flexion of the leg and also aids in medial rotation of the tibia on the femur when the knee is flexed. It also plays a role in stabilizing the knee during standing and ambulation.
While it contributes to these movements, gracilis is relatively weak and mainly acts as a synergist and stabilizer.
Synergists
For thigh adduction, gracilis works synergistically with the other adductors (adductor longus, brevis, magnus, and pectineus) to pull the thigh inward. In knee flexion, it assists the hamstrings (semitendinosus, semimembranosus, biceps femoris) and sartorius. Gracilis and semitendinosus together also medially rotate the flexed knee, complementing the action of sartorius and semimembranosus in turning the tibia inward.
Antagonists
The muscle’s hip adduction is opposed by the hip abductors (gluteus medius, gluteus minimus, tensor fasciae latae) which draw the thigh away from midline. Its knee flexion action is antagonized by the quadriceps femoris group (particularly the rectus femoris and vasti, which extend the knee). At the flexed knee, lateral rotation by biceps femoris serves as an antagonist to gracilis’ medial rotation.
Spinal Innervation
Gracilis receives innervation predominantly from the L2–L3 spinal nerve roots (with contribution from L4 in some cases) via the lumbar plexus. These nerve fibers course into the obturator nerve.
Peripheral Innervation
The anterior division of the obturator nerve innervates gracilis. This nerve passes through the obturator foramen and branches within the medial thigh to supply gracilis and other adductors.
Vasculature
Gracilis is supplied by branches of the profunda femoris artery (deep femoral artery) and the obturator artery. The medial circumflex femoral artery also contributes small muscular branches. Venous drainage is via veins corresponding to the arteries, emptying into the femoral vein.
Clinical Application
The gracilis is sometimes harvested for surgical grafts (e.g. to reconstruct hand muscles, anal sphincter, ACL repair, urethral reconstruction) due to its relative expendability and long tendon. Its removal causes minimal functional deficit because the remaining adductors compensate.
Clinically, gracilis strain or tendinopathy can occur in athletes (a type of groin strain), leading to inner thigh pain. Pes anserinus bursitis (inflammation of the bursa at the gracilis/sartorius/semitendinosus insertion) can cause medial knee pain. In gait, weakness of gracilis alone is rarely noticeable, but as part of the adductor group, it helps stabilize the leg during the stance phase. Stretching gracilis (e.g. butterfly stretch) can improve flexibility of the groin and reduce injury risk in activities requiring wide stance or rapid direction changes.
