Effect of different subtalar joint arthroereisis implants on pediatric flexible flatfoot: a finite element analysis

Flexible flat foot is a relatively common disease treated by foot and ankle surgery, and subtalar arthroereisis (STA) has gradually become favored by foot and ankle surgeons due to its advantages. However, which sinus tarsi implant is optimal remains controversial. The purpose of this study was to compare the biomechanical outcomes of two types sinus tarsi implants of different sizes via finite element analysis.

A finite element model of pediatric flexible flatfoot deformity was established in which virtual surgery of STA was simulated. Boundary and loading conditions were assumed from the data of previous finite element analysis study. The corrective ability in talar-first metatarsal angle, talonavicular coverage angle, calcaneus pitch angle, and arch height were compared and analyzed. The indexes of plantar stress distribution, the peak von Mises of medial and lateral columns, and strain of the medial ligaments were also compared and analyzed.

All the indexes were changed after the placement of the STA implants. The plantar pressure and the load of medial/lateral columns were redistributed, while the strain of the ligaments was also decreased to differing degrees. When the implants of HyProCure and Talar-Fit inserted, the parameters involved were significantly changed. Moreover, the parameters involved were changed obviously in the larger sizes of implant.

Both types of implants are beneficial in the treatment of pediatric flexible flatfoot deformity; however, HyProCure exhibited a stronger effect than did Talar-Fit. For both HyProCure and Talar-Fit, the larger sizes were better than the smaller ones.