Origin and Insertion
- Origin: Posterior surfaces of both bones of the leg (tibia and fibula) and the interosseous membrane.
- Insertion: Primarily onto the navicular bone and cuneiform bones, with partial attachments to the bases of the 2nd through 4th metatarsals.
Functions
- Foot movements: Plantarflexion, supination, and internal rotation of the foot.
- Arch support: Supports the longitudinal arch of the foot. The tendon of the tibialis posterior muscle, working together with the tendon of the m. fibularis longus, reinforces the proximal transverse arch of the foot formed by the tarsal bones.
- Clinical significance: Weakness of the supporting apparatus leads to lowering of the arch and flattening of the foot (flatfoot / pes planus).
Blood Supply and Innervation
- Blood supply: Posterior tibial artery (a. tibialis posterior).
- Innervation: Tibial nerve (n. tibialis, spinal roots L4–S1).
Topography and Neighboring Structures
- In the leg: The muscle lies in the deep flexor layer, occupying a central position. Medial to it is the m. flexor digitorum longus, and lateral to it is the m. flexor hallucis longus.
- Cruropopliteal canal (canalis cruropopliteus): The upper part of the tibialis posterior muscle forms the inferior and medial boundaries of the upper opening of the canal; laterally, the opening is bounded by the neck of the fibula, and superiorly by the popliteus muscle.
- Neurovascular bundle: Proximally, the posterior tibial neurovascular bundle lies on the posterior surface of the m. tibialis posterior. In the lower third of the leg, the muscle and its tendon shift anteriorly, causing the bundle to change position and lie on the m. flexor digitorum longus.
- Medial retromalleolar region: Here, the muscle tendon passes closest to the medial malleolus, lying in a groove on its posterior surface. It is followed by the tendon of the flexor digitorum longus.
- Synovial sheath: The tendon is enclosed in a synovial sheath (vagina synovialis m. tibialis posterioris). It begins at the level of the medial malleolus and ends at the insertion of the tendon onto the tuberosity of the navicular bone.
Clinical Diagnostics
- Motor function assessment: To detect muscle weakness objectively in tibial mononeuropathies, testing is performed on the internal rotation strength of the foot, which is driven by the m. tibialis posterior.
- Electromyography (EMG): Needle EMG of the tibialis posterior muscle is recommended. The study is typically performed 3–4 weeks after the onset of symptoms, when denervation changes—such as positive sharp waves and fibrillation potentials—reach their peak.