Definition
Acquired flat foot deformity / planovalgus foot secondary to tibialis posterior dysfunction
Etiology
Epidemiology
F > 40
Associations - hypertension / diabetes / obesity
Anatomy Tibialis Posterior
| Origin | Insertion | Nerve supply | Action |
|---|---|---|---|
|
Posterior tibia, fibula and inter-osseous membrane
Acute angle around medial malleolus - flexor retinaculum holds TP in groove - relative hypo-vascular zone 1-2cm distal to medial malleolus |
Navicular tuberosity Plantar cuneiforms 2,3,4 metatarsals Sustentaculum tali |
Tibial nerve (L4/5, S1) |
Plantar flexor ankle joint Inverts subtalar joint Adducts foot Maintains longitudinal arch Locks the midtarsal joints - allows T Achilles to perform heel raise |
Pathology
Avascular zone
- behind medial malleolus
- paratenon is supplied by blood vessels from a mesotenon on its posterior aspect
- tendon is composed of fibrocartilage where it changes direction around the med malleolus
Tendon changes
- Paratendinitis - fluid in sheath + synovial proliferation
- Tendinosis - tendon degeneration with enlargement and longitudinal splits
- Elongation of tendon
- Rupture
Deformity
Acquired planovalgus
- medial arch collapse
- subtalar joint everts / valgus heel
- foot abducts at TNJ
- Achilles tendon acts as evertor when heel in valgus
- calcaneus impinges on fibular causing lateral ankle joint pain
- attenuation of TNJ capsule, spring ligament and deltoid ligament
History
Deformity
Medial pain
Lateral pain due to fibular impingement
Difficulty with shoe wear
Examination
Planovalgus foot - flattened medial arch + valgus heel
Tenderness tibialis posterior
Too many toes sign - abducted forefoot / > 2.5 toes
Mobile / flexible subtalar joint
- moves into varus with heel raise
Tibialis posterior power
Foot inverted and in equinus
Single Heel Raise
- need working Tibialis posterior
- inverts subtalar joint & locks hind foot
- allows T Achilles to plantar flex calcaneus
X-ray
Lateral weight bearing
Early - reduced talo-metatarsal angle / Meary's angle
Late - subtalar joint OA
AP weight bearing of foot and ankle
Early - calcaneus under lateral malleolus
Late - valgus tilt of talus with ankle joint osteoarthritis
MRI
Tendonitis - fluid around tendon
Tendinopathy - tendon thickening
Tears
Tibialis posterior tendonitis
Tibialis posterior tendinopathy