Sartorius: Origin, Insertion, Nerve, Action & The "Tailor's Muscle"

The Sartorius is officially the longest muscle in the human body. It is a long, thin, strap-like muscle that runs diagonally across the anterior thigh, spiraling from the outer hip to the inner knee. It creates the "figure-4" position required to sit cross-legged.

[Image of Gracilis muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Anterior Superior Iliac Spine (ASIS) and the notch just below it.
Insertion (Distal)	Superior part of the Medial Surface of the Tibia (part of the Pes Anserinus).
Nerve Supply	Femoral Nerve (L2, L3).
Blood Supply	Femoral Artery (muscular branches).
Primary Actions	The "FABER" Pattern: • Hip: Flexion, Abduction, External Rotation. • Knee: Flexion, Internal Rotation (when knee is bent).

Deep Dive: The Tailor's Muscle

The name "Sartorius" comes from the Latin word Sartor, meaning tailor. Historically, tailors sat cross-legged on the floor to sew. The Sartorius is the muscle that puts you in this position.

1. The Spiral Path

The Sartorius crosses the thigh obliquely. It starts at the lateral hip (ASIS), crosses the anterior thigh, and ends at the medial knee. This unique path allows it to move both the hip and knee joints simultaneously in different planes.

2. The Pes Anserinus

The Sartorius is the most superficial of the three muscles that form the Pes Anserinus ("Goose's Foot") on the medial tibia.
Mnemonic: Say Grace before Tea.
• Sartorius (Femoral Nerve)
• Gracilis (Obturator Nerve)
• Semitendinosus (Sciatic Nerve)

Physio Corner: Clinical Relevance

💪 Functional Fact: We use the Sartorius constantly when getting dressed. Putting on socks or shoes requires you to bring your foot up and look at the sole (Flexion + External Rotation) — the exact action of the Sartorius.

Palpation

Have the patient sit or lie supine. Ask them to lift their leg into a "figure-4" position (foot on opposite knee). Palpate the ASIS. The strap-like muscle belly can be felt originating there and running diagonally medial-ward down the thigh.

⚠️ Clinical Pathology: Pes Anserine Bursitis
Just like the Gracilis and Semitendinosus, tight Sartorius muscles can cause friction at the medial knee insertion. This causes pain on the inner shin just below the knee joint, common in runners and cyclists.

Manual Muscle Testing (MMT)

To test the Sartorius, we must replicate the "Hackysack" or cross-legged movement.

Testing Tip: You must resist three motions at once: Hip Flexion, Abduction, and External Rotation.

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Sitting or Supine. Action: Patient flexes, abducts, and externally rotates the hip (bringing the heel toward the opposite shin). Resistance: • Hand 1: On the lateral knee, pushing down and in (Extension/Adduction). • Hand 2: On the medial ankle, pushing out (Internal Rotation).
Grade 2 (Gravity Eliminated)	Position: Supine. Heel resting on the opposite shin. Action: Patient slides the heel up the shin toward the knee. Result: Completed range of motion.
Grade 0, 1 (Palpation)	Action: Palpate just distal to the ASIS. Cue: "Try to cross your leg." Grade 1: Tendon/muscle tension felt. Grade 0: No activity.

Frequently Asked Questions

Is it a hip flexor or knee flexor?

Both! Because it crosses anterior to the hip and posterior to the knee, it flexes both joints. It is a bi-articular muscle.

Why is it the "longest" muscle?

It spans the entire length of the thigh, from the pelvis to the tibia, taking a diagonal path which adds to its total length (approx 60cm in adults), making it longer than the rectus femoris or femur itself.

What is the "Sub-Sartorial Canal"?

Also known as the Adductor Canal or Hunter's Canal. The Sartorius forms the "roof" of this tunnel in the middle third of the thigh, protecting the Femoral Artery, Vein, and Saphenous Nerve.

Test Your Knowledge: Sartorius Quiz

1. What is the origin of the Sartorius?

2. Which nerve supplies the Sartorius?

3. The Sartorius inserts into the tibia as part of the:

4. What is the "FABER" action pattern of Sartorius?

5. Which structure lies immediately DEEP to the Sartorius in the middle thigh?

6. Sartorius forms the lateral border of which anatomical space?

7. Does Sartorius extend the knee?

8. What happens to the tibia when Sartorius contracts (with knee bent)?

9. What is the nickname for the Sartorius?

10. Avulsion fractures of the ASIS in sprinters are caused by:

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Magee, D. J. (2014). Orthopedic Physical Assessment. 6th ed. Elsevier.