Tibialis Posterior: Origin, Insertion, Nerve, Action & Shin Splints

The Tibialis Posterior is the deepest, central muscle of the posterior leg (calf). It acts as the primary dynamic stabilizer of the medial longitudinal arch of the foot. Dysfunction in this muscle is a leading cause of flat feet and medial shin splints.

[Image of Dorsal Interossei Foot anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Posterior surface of the Tibia and Fibula (and the Interosseous Membrane between them).
Insertion (Distal)	Primary: Tuberosity of the Navicular bone. Expansions: All 3 Cuneiforms, Cuboid, and bases of Metatarsals 2, 3, and 4.
Nerve Supply	Tibial Nerve (L4, L5).
Blood Supply	Posterior Tibial Artery.
Primary Actions	Inversion: Turns the sole of the foot inward (Primary Inverter). Plantarflexion: Points the foot down. Arch Support: Maintains the medial longitudinal arch.

Deep Dive: The Arch Builder

The Tibialis Posterior is unique because of its extensive insertion pattern, often described as "tentacles" gripping the bottom of the foot.

1. The Tentacles

While its main attachment is the Navicular, it sends fibrous expansions to almost every tarsal bone (except the Talus) and the middle metatarsals. This extensive grip allows it to lock the bones of the midfoot together, creating a rigid arch for push-off during walking.

2. "Tom, Dick, and Harry"

This classic mnemonic describes the order of structures passing behind the Medial Malleolus (Anterior to Posterior):
Tom: Tibialis Posterior (Most anterior/closest to bone).
Dick: Flexor Digitorum Longus.
And: Posterior Tibial Artery & Nerve.
Harry: Flexor Hallucis Longus.

Physio Corner: Clinical Relevance

💪 Functional Fact: The Tibialis Posterior works eccentrically during the stance phase of gait to slow down pronation (flattening of the arch). If it fails to control this loading, the arch collapses, leading to plantar fasciitis or knee pain.

Palpation

Behind the Ankle: Palpate immediately behind the medial malleolus. Ask the patient to invert their foot ("turn your sole in"). The Tibialis Posterior is the most prominent tendon closest to the bone.
Insertion: Follow the tendon down to the Navicular tuberosity (the bony bump on the inner mid-foot).

⚠️ Clinical Pathology: Shin Splints (MTSS)
Medial Tibial Stress Syndrome is often caused by the Tibialis Posterior pulling on the periosteum of the tibia during repetitive running.
Adult Acquired Flatfoot: Chronic degeneration of this tendon leads to a progressive collapsing of the arch and a valgus heel.

Manual Muscle Testing (MMT)

We combine Plantarflexion with Inversion to isolate it from the Tibialis Anterior.

Testing Tip: The Tibialis Anterior inverts and dorsiflexes (Up and In). The Tibialis Posterior inverts and plantarflexes (Down and In).

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Resistance)	Position: Side-lying on the test side (allows gravity to resist adduction/inversion) OR Supine with ankle plantarflexed. Action: Patient inverts the foot while maintaining plantarflexion (toes pointed). Resistance: Applied to the medial border of the forefoot, pushing up and out (into Eversion/Dorsiflexion). Grade 3: Full range. Grade 4/5: Holds against resistance.
Grade 2 (Gravity Eliminated)	Position: Supine. Action: Patient slides the foot into inversion while plantarflexed. Result: Full range of motion.
Grade 0, 1 (Palpation)	Action: Palpate the tendon between the medial malleolus and navicular. Cue: "Point your toes and turn your foot in." Grade 1: Tendon pops out. Grade 0: No activity.

Frequently Asked Questions

Why is it called "Posterior"?

It is located in the posterior compartment of the leg. Its counterpart, the Tibialis Anterior, is in the anterior compartment. They are antagonists for ankle flexion/extension but synergists for inversion.

Does it attach to the Talus?

No. Despite attaching to almost every other tarsal bone to lock the arch, it skips the Talus. This allows it to move the bones around the talus (subtalar joint).

Is it deep or superficial?

It is the deepest muscle of the posterior leg, lying directly on the interosseous membrane between the tibia and fibula, covered by the Soleus and Gastrocnemius.

Test Your Knowledge: Tibialis Posterior Quiz

1. Which nerve supplies the Tibialis Posterior?

2. What is the primary insertion of the Tibialis Posterior?

3. What are the actions of Tibialis Posterior?

4. In the Tarsal Tunnel, the Tibialis Posterior tendon is:

5. Tibialis Posterior tendon dysfunction leads to:

6. Where does the Tibialis Posterior originate?

7. Which muscle is the primary antagonist for Inversion?

8. "Shin Splints" involving the Tibialis Posterior are located:

9. To MMT the Tibialis Posterior, resistance is applied to:

10. True or False: The Tibialis Posterior tendon passes anterior to the Medial Malleolus.

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.
• Brukner, P., & Khan, K. (2017). Clinical Sports Medicine. 5th ed. McGraw-Hill Education.