The tibialis posterior is the deepest muscle of the posterior leg compartment, originating from the interosseous membrane and spreading its insertion across most of the tarsal bones and metatarsal bases through an extensive fan-like attachment. It is the primary dynamic supporter of the medial longitudinal arch and the most important muscle for controlling hindfoot valgus during single-leg stance. Progressive failure of this tendon is the most common cause of adult-acquired flatfoot deformity.
| Origin | Posterior surface of the interosseous membrane; Adjacent posterior surfaces of the tibia and fibula |
|---|---|
| Insertion | Navicular tuberosity (primary attachment); Fan-like extensions to all the tarsal bones except the talus and the bases of metatarsals 2 through 4 |
| Nerve Supply | Tibial nerve (L4, L5) |
| Blood Supply | Posterior tibial artery |
| Actions | Plantarflexion of the ankle; Inversion of the foot; Supports the medial longitudinal arch during weight-bearing |
|---|
By inverting the foot and plantarflexing the ankle simultaneously it supinates the foot during push-off, converting it from a flexible adapter at heel contact to a rigid lever for propulsion, a biomechanical role that explains why its failure causes such profound gait dysfunction.
Tibialis posterior tendon dysfunction is staged I through IV by progressive severity from early tendinopathy to rigid fixed flatfoot with peritalar subluxation. The too many toes sign (excess toe visibility from behind during stance) and the inability to perform a single-leg heel rise are the key clinical assessments. Early-stage management with foot orthoses and calf strengthening can halt progression; late-stage fixed deformity requires reconstructive surgery.
The tibialis posterior tendon is palpable just posterior to the medial malleolus, where it is tender in tendinopathy. The navicular tuberosity insertion is easily felt as the bony prominence on the medial midfoot at the apex of the arch.
Degenerative overload behind the medial malleolus producing medial ankle pain and early flatfoot collapse, distinguished from a medial ankle sprain by its gradual onset and positive single-leg heel rise weakness.
Complete failure producing sudden worsening of pre-existing flatfoot, inability to perform a single-leg heel rise, and a positive too many toes sign, typically requiring surgical reconstruction.
