Functional evaluation of bilateral subtalar arthroereisis for the correction of flexible flatfoot in children: 1-year follow-up

Background: Flexible flatfoot (FFF) is a common alteration of the foot diagnosed in the pediatric population causing pain and decreased quality of life. Surgical treatment via arthroereisis of the subtalar joint can be recommended when non-invasive options do not result in sufficient pain relief. While clinical outcome of subtalar joint arthroereisis is generally positive, no functional evaluation has thus far been reported following surgery. Research question: The aim of this study was to assess the effects of two arthroereisis implants for the correction of bilateral FFF on foot and lower limb biomechanics during gait. Methods: This is a prospective study following 13 children affected by bilateral symptomatic FFF. The patients underwent bilateral subtalar arthroereisis during the same surgery using two types of poly-L-lactide bioabsorbable implants: an expanding endo-orthotic implant, and a calcaneo-stop screw. Radiological parameters and gait analysis were performed preoperatively and at 1 year follow-up and compared to those from an age-matched normal-arched control population. Lower limb and multisegment foot kinematic analysis, along with EMG of the main ankle flexor/extensor muscles, were performed during level walking at comfortable speed. Paired non-parametric Wilcoxon signed-rank test was used to assess differences in radiological and kinematic parameters between pre-op and post-op assessments. Results: All radiological parameters, and frontal-plane orientation of the rearfoot in double-leg standing were improved at 1-year follow-up in both implant groups (e.g calcaneo-stop: pre-op = 15 ± 7 deg; post-op = 6 ± 9 deg; p < 0.01). The endo-orthotic implant group showed significantly lower pronation/supination at the ankle and midtarsal joint. Activation of the tibialis anterior muscle was more physiological after surgery in both groups. Significance: According to the present analysis, both implants appear effective in restoring physiological alignment of the rearfoot, however the endo-orthotic implant appeared more effective in restoring a more correct frontal-plane mobility of foot joints.