Implant Migration and Clinical Outcomes in Pediatric Symptomatic Flexible Flatfoot Treated with Subtalar Arthroereisis: A Cohort Study with Long-Term Follow-Up Results

Abstract

Background/Objectives: Subtalar arthroereisis (STA) is a widely used surgical procedure for symptomatic pediatric flexible flatfoot. However, implant migration remains a concern due to its potential impact on long-term correction and complications. This study evaluated the migration pattern of STA implants and assessed long-term clinical and radiographic outcomes. Methods: This retrospective cohort study included 47 feet from children aged 8-13 years who underwent STA with adjunctive soft tissue procedures between 2014 and 2018, following ≥6 months of failed conservative treatment, with a minimum follow-up of 5 years. Exclusion criteria included neuromuscular or rigid flatfoot. Weight-bearing radiographs assessed anteroposterior (AP) and lateral Meary's angles, reflecting forefoot-to-hindfoot alignment, and calcaneal pitch, indicative of longitudinal arch height. Implant migration was recorded and clinical outcomes were measured by the American Orthopedic Foot and Ankle Society (AOFAS) score. Measurements were recorded preoperatively, immediately postoperatively, and at 1 month, 3 months, 6 months, 1 year, and 5 years. Results: Radiographic correction was significant and sustained at 5 years. The AP Meary's angle improved from 13.09° to 5.26° at 1 month and 6.69° at 5 years (p < 0.001); lateral Meary's angle from 9.77° to 4.06° and 4.88° (p < 0.001); and calcaneal pitch from 14.52° to 16.87° and 16.89° (p < 0.001), respectively. AOFAS scores increased from 67.52 to 90.86 at 1 month and 96.33 at 5 years (p < 0.001). Implant migration peaked within the first postoperative month (mean: 3.2 mm on ankle AP view; 3.0 mm on foot AP view) and stabilized thereafter. Four cases of complications included implant dislodgement, subsidence, and persistent sinus tarsi tenderness, which were successfully resolved after appropriate management. No recurrence of deformity was observed. Conclusions: STA implant migration is most pronounced during the first month, likely due to physiological settling as the foot adapts to altered biomechanics. With appropriate implant selection, technique, and follow-up, migration does not compromise long-term correction or outcomes. In general, symptomatic cases can often be managed conservatively prior to implant removal.

Keywords: flexible flatfoot; implant migration; long-term outcomes; pediatric orthopedics; subtalar arthroereisis.

Figure 1

The surgical technique of talonavicular joint capsule plication. (A) A linear incision was made on the medial side of the talonavicular joint, and a longitudinal window was marked. (B) The joint capsule window was incised and reflected to expose the talonavicular articulation. (C) Each capsule margin was reinforced with two non-absorbable braided sutures, which were then tied to imbricate the capsule with the foot in an inverted position, creating a medial arch.

Figure 2

An assessment of implant positioning on anteroposterior radiographs. The yellow line represents the longitudinal axis of the talus. The double-headed blue arrow indicates the width of the talar neck in the foot AP view, and the double-headed red arrow indicates the width of the talar body in the ankle AP view. The red line indicates the perpendicular distance from the implant tip to the talar axis.

Figure 3

An 8-year-old boy with bilateral flatfoot presenting with hindfoot valgus and forefoot abduction. Red lines on clinical photos illustrate hindfoot alignment in coronal plane. Yellow lines on AP and lateral radiographs represent Meary’s angles, and calcaneal pitch, respectively. (A) Preoperative clinical photograph reveals hindfoot valgus, while radiographs demonstrate an increased Meary’s angle and reduced calcaneal pitch, indicative of pes planovalgus deformity. (B) Postoperative clinical image shows the restoration of heel alignment, accompanied by radiographic correction of key parameters.

Figure 4

Early implant dislodgement in a 13-year-old boy who sustained an ankle sprain 1 month postoperatively. (A) An immediate postoperative AP radiograph demonstrating appropriate implant placement. (B) A follow-up radiograph at 1 month showing dislodgement of the implant with loss of correction. (C) Five-year radiographic follow-ups showed the implant in a good position.

Figure 5

Implant subsidence in a 10-year-old girl who underwent STA and later sustained an ankle sprain. (A) A preoperative AP radiograph of the left foot showing forefoot abduction deformity. (B) An AP radiograph at 7 months postoperatively reveals subsidence of the STA implant following a sprain injury. (C) A radiograph taken 1 year postoperatively also demonstrates implant subsidence. (D) Bone union was achieved following revision surgery with lateral column lengthening.