Abstract
Background
Flexible flatfoot is a common pediatric condition characterized by a reducible loss of the medial longitudinal arch during weight-bearing. While subtalar arthroereisis is widely used for its minimally invasive correction, long-term outcomes—particularly arch stability after implant removal—remain poorly understood. This study evaluates radiological and functional changes from implant insertion to removal in adolescent flatfoot patients.
Methods
A retrospective analysis of 21 adolescents with flexible flatfoot who underwent subtalar arthroereisis followed by implant removal was conducted. Radiographic parameters (hindfoot valgus angle, talonavicular coverage angle, etc.) and functional scores (AOFAS, VAS) were assessed preoperatively, postoperatively, and at final follow-up (mean 8.2 years).
Results
Subtalar arthroereisis significantly improved deformity and function. The hindfoot valgus angle reduced from 11.6° ± 7.8° to 1.3° ± 4.3° postoperatively, AOFAS score increased from 68.3 ± 6.2–95.5 ± 3.0. The talonavicular coverage angle was 26.2 ± 11.4° preoperatively, decreased to 10.1 ± 5.9° postoperatively. The talar pitch angle was 40.9 ± 6.0° preoperatively, decreased to 29.3 ± 3.4° postoperatively. The calcaneal pitch angle was 14.2 ± 2.2° preoperatively, increased to 16.9 ± 2.9° postoperatively. The lateral Meary’s angle was −24.4 ± 6.9° preoperatively, improved to −8.1 ± 3.5° postoperatively. The AOFAS score increased from 68.3 ± 6.2 preoperatively to 95.5 ± 3.0 postoperatively, meanwhile, the VAS score decreased significantly from 3.5 ± 1.2 preoperatively to 1.3 ± 1.1 postoperatively. However, mild arch recurrence occurred after implant removal (The talar pitch angle increased to 32.6 ± 3.3° at the final follow-up. The lateral Meary’s angle increased to −12.9 ± 3.6° at the final follow-up after implant removal.), though values remained superior to preoperative levels.
Conclusion
Following subtalar arthroereisis implant removal, adolescents with flexible flatfoot demonstrate mild arch recurrence; nevertheless, radiological outcomes sustain substantial improvement relative to the preoperative condition.
1
Introduction
Flatfoot, characterized by a reducible loss of the medial longitudinal arch during weight-bearing, is a common condition in children and adolescents ,, . While most cases remain asymptomatic, a subset develop progressive hindfoot valgus, chronic pain, or functional limitations refractory to conservative management. Flatfoot is broadly categorized as flexible or rigid. Flexible flatfoot typically presents with a reducibly low or absent medical longitudinal arch, hindfoot valgus, and forefoot abduction, with or without tightness of the gastrocnemius or gastrocnemius-soleus complex .
Current management strategies range from conservative measures, such as physical therapy and orthotic devices, to surgical interventions for refractory cases. Surgery is indicated when conservative methods fail. Numerous surgical procedures address pediatric and adolescent flatfoot. Among these, subtalar arthroereisis is frequently employed due to its minimally invasive nature and relatively short recovery period ,, . Numerous studies have demonstrated that subtalar arthroereisis yields significant improvement in radiographic parameters and clinical outcomes ,,, . While correction is achieved biomechanically through talotarsal realignment, it remains unknown whether this correction persists after implant removal or if the remodeled soft tissues can maintain the arch independently. This gap is critical as recurrent deformity would undermine the procedure’s durability. However, no studies have investigated whether arch collapse recurs following implant removal. Therefore, the purpose of this study was to evaluate changes in radiological and functional outcomes between subtalar arthroereisis surgery and subsequent implant removal surgery.
2
Methods
2.1
Study Design and Population
Approval for this retrospective study was obtained from our hospital’s ethics committee. Data were collected from August 2014 to December 2020. Twenty-one adolescent patients with flexible flatfoot who underwent subtalar arthroereisis and subsequent implant removal were included.
2.2
Inclusion criteria
(1) Age < 18 years at initial surgery; (2) Diagnosis of flexible flatfoot; (3) Underwent primary subtalar arthroereisis; (4) Underwent scheduled implant removal; (5) Availability of preoperative weight-bearing radiographs (AP/lateral), immediate postoperative radiographs, and radiographs obtained after implant removal.
2.3
Exclusion criteria
(1) Rigid flatfoot (e.g., tarsal coalition); (2) Incomplete radiographic series (preoperative, postoperative, or post-removal) or failure to undergo implant removal; (3) Age ≥ 18 years at initial surgery; (4) Concurrent or additional procedures (e.g., osteotomy, arthrodesis).
2.4
Radiographic assessment
Standardized weight-bearing foot radiographs (anteroposterior and lateral projections) were obtained. The following parameters were measured: hindfoot valgus angle, talar pitch angle, calcaneal pitch angle, lateral Meary’s angle, and talonavicular coverage angle. All radiographs were performed under standardized load-bearing conditions and by the same radiology team.
2.5
Functional assessment
Functional outcomes were assessed using the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Score and the Visual Analog Scale (VAS) for pain.
2.6
Surgical technique
The patient was placed supine on the operating table. A small incision about 1 cm was performed at the sinus tarsi site. The HyProCure implant (GraMedia, Macomb, MI) was used for extraosseous stabilization. Blunt dissection of subcutaneous tissues and ligaments was performed. A guidewire was inserted into the tarsal canal. The HyProCure implant (GraMedica, Macomb, MI) was employed for extraosseous talotarsal stabilization. Intraoperative fluoroscopy was utilized to confirm proper implant positioning, with the device’s central axis aligned along the longitudinal talar bisection line and its lateral component in contact with the talus’ lateral surface. During the operation, weight-bearing simulation was performed to assess whether the flatfoot deformity was corrected after subtalar arthroereisis. If the correction was insufficient, a larger implant size was selected; if the correction was excessive, a smaller implant size was chosen. This iterative process continued until satisfactory flatfoot correction was achieved.
If accessory navicular resection is required, an approximately 2 cm incision is made along the medial foot to expose the posterior tibial tendon and accessory navicular. The accessory navicular is resected along its margins, followed by suture anchor implantation into the navicular body for reattachment of the posterior tibial tendon. Notably, a thin bone fragment should be preserved on the posterior tibial tendon side of the accessory navicular to facilitate bony union with the native navicular, thereby enhancing the strength of the posterior tibial tendon.
2.7
Postoperative management
Patients initiated partial weight-bearing in a supportive boot at 2 weeks postoperatively. Clinical and radiographic follow-up occurred at 2 weeks, 6 weeks, 3 months, and 1 year. Implant removal was routinely recommended at 1 year. All patients were followed until at least 18 years of age.
2.8
Implant removal
All patients underwent implant removal surgery approximately one year postoperatively. Immediate full weight-bearing was permitted.
2.9
Statistical methods
Analyses were performed using SPSS version 20 (IBM, NY, USA). Continuous data are presented as mean ± standard deviation. Statistical significance was set at p < 0.05. Paired t -tests were likely used for comparisons.
3
Results
Twenty-one patients (15 males, 6 females) were included. The mean age at initial surgery was 13.0 ± 1.9 years. The mean interval between arthroereisis and implant removal was 13.3 ± 3.9 months. Mean total follow-up duration was 8.2 ± 2.0 years ( Fig. 1 , Fig. 2 ).
The clinical course of an 11-year-old boy with flexible flatfoot. Panel A (preoperative) demonstrates significant collapse of the medial longitudinal arch with evident talar head depression. Following subtalar arthroereisis implantation (Panel B), substantial restoration of the arch height and talar head alignment correction are observed. However, Panel C (long-term follow-up after implant removal) reveals mild recurrent talar head depression, suggesting partial loss of correction over time.
Another case of a 12-year-old boy with flexible flatfoot. Panel A (preoperative) shows the initial foot deformity, Panel B demonstrates the postoperative correction following subtalar arthroereisis implantation, and Panel C (final follow-up after implant removal) reveals the long-term outcome.
The radiographic measurements demonstrated significant changes throughout the treatment process: the hindfoot valgus angle was 11.6 ± 7.8° preoperatively, reduced to 1.3 ± 4.3° postoperatively, and increased to 3.7 ± 5.6° at the final follow-up after implant removal. The talonavicular coverage angle was 26.2 ± 11.4° preoperatively, decreased to 10.1 ± 5.9° postoperatively, and increased to 12.2 ± 8.1° at the final follow-up. The talar pitch angle was 40.9 ± 6.0° preoperatively, decreased to 29.3 ± 3.4° postoperatively, and increased to 32.6 ± 3.3° at the final follow-up. The calcaneal pitch angle was 14.2 ± 2.2° preoperatively, increased to 16.9 ± 2.9° postoperatively, and slightly decreased to 16.6 ± 3.3°. The lateral Meary’s angle was −24.4 ± 6.9° preoperatively, improved to −8.1 ± 3.5° postoperatively, and moderately increased to −12.9 ± 3.6° at the final follow-up after implant removal. From a statistical perspective, the recurrence of adolescent flexible flatfoot after subtalar arthroereisis implant removal is primarily associated with changes in the talar tilt angle and Meary’s angle ( Fig. 3 ).
The radiographic measurements critical for foot and ankle assessment include: Meary’s angle (Angle 1), defined on lateral weight-bearing radiographs as the angle between the longitudinal axis of the first metatarsal and the talar axis, which quantifies medial arch collapse; Talar inclination angle (Angle 2), measured on lateral views as the angle formed by the talar axis relative to the horizontal plane, indicating talar positional abnormalities; Hindfoot valgus angle (Angle 3), determined exclusively on standardized hindfoot alignment views (Saltzman view) as the intersection angle of the tibial axis and calcaneal longitudinal axis, essential for evaluating frontal plane deformity; Talonavicular coverage angle (Angle 4), captured on anteroposterior radiographs as the angle between the distal articular surface line of the talus and proximal articular surface line of the navicular, revealing midfoot instability; and Calcaneal pitch angle (Angle 5), calculated on lateral radiographs as the angle between the inferior calcaneal cortex and horizontal plane, reflecting calcaneal positioning.
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