Gracilis: hip adduction and knee flexion
Gracilis is a slender muscle on the inner thigh that adducts the thigh at the hip (pulls it towards the midline) and helps to flex the knee.
Remember
A medial thigh muscle that crosses both the hip and the knee is gracilis: it adducts the thigh and helps to flex the knee.
Memory aid
the adductor that goes past the knee
If an inner-thigh muscle also bends the knee, think gracilis.
Gracilis is the most superficial and most medial of the muscles in the medial compartment, the group of muscles on the inner side of the thigh. It starts on the pubis (the front part of the pelvis, near the groin) and runs down the inner thigh to the medial surface of the tibia (the shin bone).
Where it passes the hip, gracilis pulls the thigh towards the midline, which is called hip adduction. Because it then continues across the knee, it also contributes to knee flexion (bending the knee). Gracilis spans two joints, so its adduction at the hip and its flexion at the knee follow directly from its attachments and its position on the inner thigh.
The knee action is the clue that identifies gracilis among the muscles of the medial compartment. Adductor longus (an adductor, a muscle that pulls the thigh towards the midline) is described as adducting the thigh only. Of the five muscles in the medial compartment, gracilis is the one that attaches to the tibia, while the other four attach to the femur and act only at the hip.
Knee extension is the job of the quadriceps (the large muscle group at the front of the thigh), and not of gracilis. Weakness at both the hip and the knee from one medial thigh injury points to a muscle that crosses both joints.
Key facts
- Course
- it arises from the pubis and attaches to the medial surface of the tibia, crossing both the hip and the knee.
- Hip action
- adduction, pulling the thigh towards the midline.
- Knee action
- flexion of the leg at the knee.
- Position
- the most superficial and most medial muscle of the medial thigh compartment.
- Two-joint clue
- weakness at both the hip and the knee from one medial thigh injury points to a muscle that crosses both joints.
Exam traps
- Involving the same two joints does not make a muscle gracilis: rectus femoris (the part of the quadriceps that crosses both the hip and the knee) flexes the hip and extends the knee, but gracilis is an adductor at the hip and a flexor at the knee.
- Hip adduction with lateral rotation does not describe gracilis: it describes obturator externus, another medial thigh muscle, and gracilis assists knee flexion rather than lateral rotation of the hip.
- Weak hip adduction alone does not point to gracilis: adductor longus also adducts the thigh, but its attachments on the pubis and the femur mean it does not cross the knee, so its loss does not explain reduced knee flexion.
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