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Tibialis posterior tendon (lateral slips)

The tibialis posterior tendon (TPT) is the key dynamic stabilizer of the medial longitudinal arch of the foot. While its main tendon inserts onto the navicular tuberosity, it gives off multiple lateral slips that expand widely to insert on several tarsal and metatarsal bones. These lateral expansions are critical for maintaining midfoot integrity and resisting arch collapse.

The lateral slips play a central role in the biomechanics of the foot, distributing load and stabilizing multiple joints. Dysfunction or rupture of these slips contributes significantly to posterior tibial tendon dysfunction (PTTD) and adult-acquired flatfoot deformity.

Synonyms

  • Accessory insertions of the tibialis posterior tendon

  • Lateral expansions of tibialis posterior

  • Distal slips of posterior tibial tendon

Origin, Course, and Insertions

  • Origin: Tibialis posterior muscle arises from the posterior surfaces of the tibia, fibula, and interosseous membrane (proximal origin of tendon).

  • Course: Tendon runs posterior to the medial malleolus within the tarsal tunnel, held by the flexor retinaculum. After crossing the ankle joint, it divides distally into a main central band and multiple slips.

  • Insertions (lateral slips):

    • Cuneiforms (medial, intermediate, lateral)

    • Cuboid

    • Bases of the 2nd, 3rd, and 4th metatarsals

    • Occasionally the sustentaculum tali and other midfoot structures

Relations

  • Superiorly: Flexor digitorum longus and posterior tibial artery in the tarsal tunnel

  • Inferiorly: Spring ligament (calcaneonavicular ligament) supporting the tendon

  • Medially: Medial malleolus, flexor retinaculum, and navicular tuberosity (main insertion site)

  • Laterally: Expansions over the plantar aspect of the midfoot towards cuneiforms and metatarsals

Function

  • Medial arch support: Major dynamic stabilizer of the medial longitudinal arch

  • Plantarflexion and inversion: Works with tibialis anterior to invert and plantarflex the foot

  • Load distribution: Lateral slips help transmit force across midfoot bones

  • Stability: Prevents valgus collapse of the hindfoot and abduction of the forefoot

Clinical Significance

  • Posterior tibial tendon dysfunction (PTTD): Progressive degeneration of tendon and its slips leads to adult-acquired flatfoot

  • Tears/ruptures: Can involve the main tendon or lateral slips, leading to loss of arch support

  • Overuse injuries: Common in athletes, dancers, and patients with pronated foot posture

  • Surgical relevance: Reconstruction or tendon transfers often target or involve tibialis posterior tendon and its lateral slips

MRI Appearance

  • T1-weighted images:

    • Normal tendon: low signal (dark cord-like structure)

    • Lateral slips: thin, low-signal bands inserting into cuneiforms/metatarsals

    • Tendinopathy: thickened tendon with intermediate signal intensity

    • Surrounding fat: bright, aiding visualization

  • T2-weighted images:

    • Normal tendon: dark (even darker than on T1)

    • Tears or degeneration: bright hyperintense signal within tendon or slips

    • Fluid around tendon sheath indicates tenosynovitis

  • STIR:

    • Normal tendon: low signal

    • Pathology: hyperintense edema or fluid within or surrounding tendon

    • Useful for detecting subtle tears and peritendinitis

  • Proton Density Fat-Saturated (PD FS):

    • Normal: uniformly dark

    • Tendinopathy/partial tear: bright intratendinous signal without full-thickness gap

    • Complete tear: discontinuity with fluid-bright signal replacing tendon

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: minimal or no enhancement

    • Synovitis or peritendinitis: enhances strongly

    • Partial tears: peripheral enhancement around tendon edges

CT Appearance

Non-Contrast CT:

  • Tendon appears as soft-tissue density, not well visualized

  • Chronic tendinopathy may show calcifications or ossification along tendon insertions

  • Bony changes at insertions: cortical irregularity, sclerosis

Post-Contrast CT (standard):

  • Muscle and surrounding soft tissue enhance

  • Tendon itself remains non-enhancing

  • Peritendinous inflammatory changes may be indirectly visualized

MRI image

Tibialis posterior tendon (lateral slips) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Tibialis posterior tendon (lateral slips) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001