Flatfoot in Adults-2
Posterior Tibial Tendon Dysfunction
– Tib post inserts into the plantar aspect of the navicular and into the medial and middle cuneiforms
– main function of the tendon is to invert the subtalar joint (stabilizes the hindfoot with gastrocs) and adduct the forefoot; inverting the heel stabilizes the subtalar joint.
– the peroneus brevis is the main antagonist, everting the subtalar joint and abducting the forefoot
– if the tib post is weak, the peroneus brevis is a significant deforming force (conversely, if peroneus brevis is disrupted, the hindfoot is pulled into varus and the forefoot into adduction by tib post)]
– tib post dysfunction is largely a degenerative problem, preceded by synovitis.
– the history is that of a slow progressive discomfort
– physical demonstrates significant sagging of the medial malleolus and talar head, with the forefoot abducted. Standing on toes is difficult, and the calcaneus will not invert.
– ankle joint motion is usually good, but subtalar motion is variable, as is transverse tarsal motion; these are important to note in planning treatment
– muscle strength can be tested by resisted inversion in plantarflexion (to decrease the influence of tib ant) and in maximal eversion.
– look for the relationship between the forefoot and the hindfoot; as the hindfoot falls into valgus, the forefoot may swing into varus and this deformity may become fixed. This may need to be corrected.
– careful physical exam to note synovial thickening, subtalar motion, ankle motion, transverse tarsal motion, and the degree of hindfoot versus forefoot rotation.
– if synovitis is the major problem, try an NSAID and cast immobilization
– if chronic and rigid, try foot orthosis
– if flexible, try an orthosis or UCBL insert
– Surgery: reconstruction or fusion
– for reconstruction, the foot must be supple in both the hindfoot and forefoot; if the mobility is not present, or the forefoot varus is too advanced, a tendon transfer will fail.
– tendon transfer is probably superior in young patients with supple feet
– Mann describes a technique of reconstructing tib post with flexor digitorum longus strung up into the navicular.
-Arthrodesis – the basic premise is that the more flexible the foot, the less disability the patient has
– what to fuse depends on what the anatomy is. Options include
– isolated subtalar fusion if there is a supple, easily correctable transverse tarsal joint and no fixed forefoot deformity
– talonavicular arthrodesis – if subtalar joint and forefoot are flexible.
– double arthrodesis – talonavicular and calcaneocuboid – if subtalar joint is supple
– triple arthrodesis – must get the hindfoot back to neutral or 5o of valgus
– has a predilection for the forefoot, with ankle involvement.
– rarely involves the tarsometatarsal joints
– treatment involves immobilization, perhaps AFO; surgery should be aggressive before huge deformity exists.
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