Background: Posterior tibial tendon dysfunction (PTTD) is characterized by degeneration of this tendon leading to a flattening of the medial longitudinal arch of the foot. Foot orthoses (FOs) can be used as a treatment option, but their biomechanical effects on individuals with PTTD are not yet fully understood.
Research question: The aim of this study was to investigate the effects of three types of FOs on gait biomechanics in individuals with PTTD.
Methods: Fourteen individuals were recruited with painful stage 1 or 2 PTTD based on Johnson and Strom's classification. Quantitative gait analysis of the affected limb was performed in four conditions: shoes only (Shoe), prefabricated FO (PFO), neutral custom FO (CFO) and custom varus FO (CVFO) with a 5° medial wedge and a 4 mm medial heel skive. A curve analysis, using 1D statistical parametric mapping, was undertaken to assess differences in lower limb joint motion, joint moments and muscle activity over the stance phase of gait across conditions.
Results: Decreased hindfoot eversion angles, decreased ankle inversion moments and increased ankle eversion moments were observed with custom FOs compared to the Shoe and PFO conditions (p < 0.001). CFOs and CVFOs induced an increased knee abduction moment compared to Shoe (p < 0.001). No changes in hip kinematics and kinetics or in EMG activity of tested muscles were observed between conditions.
Significance: Custom orthoses may be more suitable than PFOs to decrease the pathological biomechanical outcomes observed in PTTD. Decreased ankle inversion moments during the stance phase could explain why custom orthoses are effective at reducing pain in PTTD patients. However, clinicians should be careful when prescribing custom orthoses for PTTD since unwanted collateral biomechanical effects can be observed at the knee.
Keywords: Foot orthoses; Gait; Posterior tibial tendon dysfunction; Tendon; Three-segment foot model; Tibialis posterior muscle.
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