Pes Planus                                                                                                             Issue No. 42

Dysfunction of the tibialis posterior has been identified as one of the primary causes of adult acquired flatfoot (pes planus). Today, we'll review a study by Kulig et al. that examines the influence of shoes and orthoses on tibialis posterior activation in patients with a pes planus foot.  



Cherri Choate, DPM
Larry Huppin, DPM
Alona Kashanian, DPM
Paul R. Scherer, DPM
Effect of Foot Orthoses on Tibialis Posterior Activation in Persons with Pes Planus

Foot orthoses are frequently prescribed for symptomatic pes planus in an effort to more properly align the foot. Adults with a normal arch selectively recruited the tibialis posterior during resisted foot adduction and plantar flexion. This study evaluates muscle recruitment in asymptomatic adults with pes planus.



  • n = 6
  • Subjects performed closed chain resisted foot adduction under two conditions: barefoot and shod with foot orthoses
  • Intensity of muscle activation was evaluated using MRI immediately before and after exercise
  • Multivariate analyses of signal intensity was performed for tibialis posterior, medial gastrocnemius, soleus, peroneus longus, and tibialis anterior


  • When barefoot, five subjects activated other lower-leg muscles in addition to tibialis posterior
  • When wearing the foot orthoses and shoes, the same subjects activated only the tibialis posterior
  • Tibialis posterior activity nearly doubled with orthoses use compared to the barefoot condition
Significance of the Article

This study shows that the use of foot orthoses and shoes resulted in selective and more effective tibialis posterior activation during the exercise compared with the barefoot condition. Activity in the tibialis posterior nearly doubled whereas the remaining muscles were quiescent. Further, the pattern of muscle activation while using the orthoses mimicked those previously described when persons with a normal arch index performed the exercise barefoot. The authors state that "wearing foot orthoses and shoes improved selective activation of the TP [tibialis posterior] in persons with flat feet."

Significance for Orthotic Therapy

A pes planus foot frequently has a hindfoot valgus, midfoot varus, and forefoot abductus posture. In this position, the navicular, the primary tarsal insertion site of the tibialis posterior, is lowered. This malalignment may necessitate activation of other muscles of the foot-ankle complex to assist in functions normally performed primarily by the tibialis posterior. The authors propose that changes in the alignment of the rearfoot and arch while using orthoses may have altered the lever arms, and contributed to differences in muscle activation patterns. Based on the findings of this study, the authors suggest that people with pes planus wear foot orthoses, even while performing rehabilitative strengthening exercises.