1 Introduction

Hallux valgus is a common foot deformity that causes pain and significantly affects functionality. It impacts sedentary individuals and athletes, with a prevalence rate exceeding 35 %.^1–3 Among the surgical techniques for its correction, minimally invasive procedures such as the Chevron-Akin technique⁴ stand out, and more recently, the use of devices to displace the metatarsal head has been introduced.⁵

Various studies have evaluated the effects of different surgical techniques on foot width. Panchavi et al.⁶ found an average decrease of 8.7 mm in postoperative radiographic foot width following a combined Chevron + Akin surgery. Neufeld et al.⁷ reported an average reduction in bony width of 5.6 % and soft tissue width of 3.8 %. Our research group observed in 2022, after Scarf-type osteotomies, a 5 % decrease in bony foot width and a 2 % decrease in soft tissues,⁸ similar to the findings of Tenenbaum et al., in 2018 with the same technique.⁹ Vieira Cardoso et al. compared open and percutaneous Lapidus procedures, showing significant results.^10,11

Foot width correction is a critical aspect of foot surgery, significantly influencing patient satisfaction. Even when radiological angles are not completely corrected, patient satisfaction can remain high, especially when they can wear tighter or heeled shoes. To our knowledge, proximal width has not been fully studied in MIS surgery. El Masry S et al.¹² provide data on forefoot width, considering two measurements: the distal measurement, which has been mostly evaluated referencing the head of the first and fifth metatarsals, and a new measurement from the head of the fifth to the middle third of the first metatarsal. Therefore, it is crucial to continue contributing more data regarding these changes.^13,14

This study aims to evaluate the efficacy of the fourth-generation MICA technique in correcting proximal foot width. It compares measurements in bony and soft tissues from the base of the first metatarsal to the base of the fifth metatarsal. This measurement will allow for a comprehensive analysis of the surgery's impact on foot structure, considering both bony and soft tissue width. The expected results will provide valuable information to optimize the surgical management of hallux valgus and improve patient satisfaction.

2 Methods

After obtaining approval from the institutional ethics committee and informed consent from all patients, we conducted a retrospective comparative study of 107 patients (163 feet). Two evaluators trained in ankle and foot surgery radiographically measured the forefoot width (bony and soft tissues) using Enterprise Imaging XERO Viewer 8.1.2 (Agfa HealthCare N.V., Mortsel, Belgium) in patients who underwent minimally invasive Chevron-Akin surgery (MICA) for symptomatic hallux valgus performed by two independent foot and ankle surgeons with over 20 years of experience at a single institution between April of 2020 and November of 2022. The bony width (BW) and soft tissue width (STW) of the foot were measured on weight-bearing anteroposterior (AP) radiographs as previously described by Jung et al.,¹⁵ recording the maximum distance from the medial edge of the first metatarsal head to the lateral edge of the fifth metatarsal head and from the most medial soft tissue shadow to the most lateral soft tissue shadow, repeating the procedure at the base to record proximal width. BW and STW measurements were taken preoperatively and six months after surgery (Fig. 1).

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Fig. 1 Pre (left) and postoperative (at six months, right) measurements of bone and soft tissue width, both distal and proximal of the foot. On weight-bearing anteroposterior radiographs of the foot.

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Inclusion criteria were patients aged 18 or older with painful hallux valgus trated with MICA technique, excluding patients with any neurovascular or inflammatoy diseases, fractures or previous surgeries on the ankle and foot and those without pre- and postoperative images taken at the same centre, as these measurements were calibrated and recorded by two radiology technicians exclusively assigned to foot and ankle pathologies. In the end, 26 patients were excluded based on these criteria as 15 had previous foot surgeries and 11 underwent concomitant fifth toe bunionectomy, resulting in a final study sample of 81 patients (132 feet).

3 Surgical technique

The surgical technique used follows the principles described by Redfern and Vernois⁴ and was applied uniformly in all cases. Under tight tourniquet and regional ankle anesthesia, an extra-articular osteotomy was performed with a 2 × 20 mm burr through a percutaneous incision at the metatarsal neck under fluoroscopic guidance with a mini C-arm. Then, a device was used to displace the metatarsal head (Figs. 2 and 3), and two parallel pins were passed from proximal to the head using the device as a guide, followed by drilling and placement of 4.0 and 3.0 mm bevelled screws. The next step involved a proximal phalanx osteotomy with a Kirschner wire inserted anterogradely from the medial base of the proximal phalanx to the lateral neck. The wire was then retracted just proximal to the osteotomy site, completed with a burr and fixed with a 2.5 mm screw. Finally, the medial edge and any prominent medial exostosis were excised. All patients were allowed to bear weight in a flat postoperative shoe immediately after surgery for at least two weeks until suture removal, after which they used regular shoes as tolerated if swelling permitted.

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Fig. 2 Placement of device to displace the metatarsal head.

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Fig. 3 Displacement of at least 100 per cent of the metatarsal head to the left application of the device to the right fluoroscopic image.

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4 Statistical analysis

Data were analyzed descriptively using means, modes, and percentages for demographic variables. Intraclass correlation coefficients (ICC) were calculated to measure agreement between the two independent observers, and the average of these measurements was used for variable analysis. T-tests and Wilcoxon tests were used to compare differences between pre-and postoperative HVA, IMA, DMAA, bony width, and soft tissue width. Pearson correlation coefficients were calculated to determine if HVA, IMA, and DMAA were associated with bony and soft tissue width. A post-hoc analysis was performed to establish the statistical power of the results. A p-value of less than 0.05 was considered statistically significant. All statistical calculations and analyses were performed using SPSS version 28.0.1.1 (SPSS, Inc. an IBM company, Chicago IL).

5 Results

Demographic data are shown in Table 1. There were 81 patients with a total of 132 feet (76 women, 5 men; 61 left, 71 right), with an average follow-up of 18.4 ± 2.7 months (range 13–24). The average age of the patients was 48.48 ± 15.07 years (range 18–74). All patients received minimally invasive Chevron and Akin osteotomies as described above.

Pre- and postoperative angular parameters of HV deformity are shown in Table 2. The average preoperative and postoperative HVA were 26.59 ± 7.47° and 9.36 ± 5.96°, respectively (P < 0.001). The average DMAA was 21.2 ± 12.80° before surgery and decreased to 7.55 ± 8.25° after surgery (P < 0.001). The IMA averaged 12.86 ± 2.97° before surgery and decreased to 5.62 ± 4.05° after surgery (P < 0.001). All angles—IMA, HVA, and DMAA—had a direct relationship with the reduction in both bony and soft tissue width.

The ICCs showed excellent inter-observer reliability >0.9 (ICC ranges 0.851–0.988) for all pre-and postoperative radiographic variables measured (Table 3).

Our data showed significant reductions in both forefoot and proximal foot widths postoperatively. Bony foot width decreased from an average of 83.02 mm–77.35 mm (p < 0.001), while soft tissue foot width decreased from an average of 101.66 mm–95.23 mm (p < 0.001). Proximal bony width showed a significant reduction from 68.79 mm to 65.82 mm (p < 0.001), and proximal soft tissue width also showed a reduction from 87.46 mm to 85.92 mm (p < 0.001). Pearson correlation analysis showed that changes in HVA, IMA, and DMAA were significantly correlated with changes in both bony and soft tissue width (p < 0.001). The post-hoc power analysis confirmed a power of 0.95, indicating that our sample size was sufficient to detect these differences. Table 4 summarises the most relevant findings regarding variations in foot width. These results underscore the importance of analysing both forefoot and proximal widths.

6 Discussion

Hallux valgus surgery aims to correct deformity, relieve pain, and improve foot function, often assessed through the correction of angular parameters such as the hallux valgus angle (HVA), intermetatarsal angle (IMA), and distal metatarsal articular angle (DMAA). However, reducing foot width is crucial for patient satisfaction, particularly in achieving a comfortable shoe fit. Our study is the first to evaluate the impact of fourth-generation minimally invasive Chevron and Akin (MICA) surgery on proximal foot width.

Our data revealed a significant reduction in distal bony width from 90.0 mm to 83.0 mm (p < 0.001) and a decrease in distal soft tissue width from 102.0 mm to 100.0 mm (p = 0.006). These findings align with those reported by Conti et al.,⁸ who observed a reduction in forefoot width of approximately 8.9 mm (radiographic) and 7.9 mm (weight-bearing CT) following hallux valgus correction. Similarly, Jung et al.⁴ documented a 16 % reduction in forefoot width after proximal Chevron osteotomy and Akin procedure. These reductions in distal width reflect the angular corrections achieved during surgery, particularly in the hallux valgus angle (HVA) and intermetatarsal angle (IMA), which showed significant improvements in our study from 26.50° to 9.48° and from 12.98° to 5.77°, respectively. Conversely, proximal bony and soft tissue widths increased in 48.5 % and 65.2 % of cases, respectively, a finding not previously reported in the literature. Specifically, the proximal bony width increased on average from 5 % (68.5 mm–70.0 mm, p < 0.001), and the proximal soft tissue width increased from 6 % (84.0 mm–87.0 mm, p < 0.001). This result contrasts with the distal narrowing and raises questions about the redistribution of mechanical loads and soft tissue adaptation following surgery.

Traditional angular measurements, such as HVA, IMA, and DMAA, demonstrated significant improvements in our cohort, but their relationship with changes in foot width appears more evident in the distal region. The differing patterns observed in proximal width, with limited correlation to other established parameters, emphasize the need to evaluate the entire foot structure rather than focusing solely on distal aspects.

Two possible causes can be proposed: first, the hyper-adduction maneuver of the first metatarsal as part of the surgical technique, which may vary depending on the use of devices to position the metatarsal head over the sesamoids; and second, underlying instability of the tarsometatarsal (TMT) joint before and during the procedure. This finding could hold clinical significance, particularly regarding patient-reported outcomes such as shoe fit and overall satisfaction. While the reduction in distal width meets patient expectations for a slimmer forefoot, changes in the proximal area may impact comfort, function, or long-term biomechanical performance.

One limitation of our study is its retrospective design, which did not include preoperative patient-reported outcome measures (PROMs), and the lack of long-term follow-up to assess whether these changes persist over time.

7 Conclusion

This study highlights significant findings regarding the structural changes in foot width following minimally invasive hallux valgus surgery. Nearly half of the cases showed an increase in proximal bony width, while over 65 % exhibited soft tissue enlargement. Introducing proximal foot width as a novel parameter provides valuable insights into post-surgical adaptations, emphasizing its relevance for understanding biomechanical changes. However, further research with larger cohorts and extended follow-up is essential to validate these findings, explore the underlying mechanisms of proximal width changes, and evaluate the long-term benefits and durability of the MICA technique.

Patient consent

Written informed consent was obtained from all patients included in the study. No minors or legally incapacitated individuals were involved.

CRediT author statement

- Ronald Isaac Ramos Ruiz: Conceptualization, Methodology, Writing – Original Draft.- Cristian Ortiz Mateluna: Investigation, Data Curation.- Manuel Pellegrini Pucci: Formal Analysis, Visualization.- Giovanni Carcuro Urresti: Resources, Writing – Review & Editing.- Felipe Chaparro Ravazzano: Supervision, Project Administration.- Ana Butteri: Validation, Writing – Review & Editing.

Ethical approval

This study was approved by the Ethics Committee of Universidad de los Andes, Santiago de Chile.

All procedures were conducted in accordance with the Declaration of Helsinki and international ethical standards.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.