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Abstract

Background:

Minimally invasive surgery (MIS) for hallux valgus, particularly the minimally invasive chevron and Akin (MICA) technique, is gaining popularity. However, comparative studies between open scarf-Akin osteotomy (SA) and MICA remain limited, particularly for severe cases (ie, hallux valgus angle [HVA] ≥ 40° or intermetatarsal angle [IMA] ≥ 16°). This study aimed to compare the clinical and radiographic outcomes between SA and MICA for severe hallux valgus.

Methods:

We retrospectively reviewed 56 consecutive feet (SA = 33; MICA = 23) treated between January 2019 and January 2023 at a single institution in Hong Kong. Clinical outcomes were evaluated using the American Orthopaedic Foot & Ankle Society (AOFAS) score, Self-Reported Foot and Ankle Score (SEFAS), and visual analog scale (VAS) for pain. Radiographic parameters included the HVA, IMA, distal metatarsal articular angle (DMAA), first metatarsal pronation, and first metatarsal length.

Results:

Baseline characteristics were broadly comparable, with deformity severity trending higher in MICA. MICA had shorter total operative time and hospital stay (P = .002 and P < .001), although the SA group had a higher frequency of concomitant lesser-toe procedures (85% vs 61%, P = .056), and MICA showed greater improvements in AOFAS and SEFAS (P = .006 and P = .032). In exploratory 2-predictor sensitivity regression adjusting for concomitant lesser-toe procedure, MICA remained associated with shorter operative time (beta = −40.0 min, 95% CI −66.3 to −13.7; P = .003) and shorter length of stay (beta = −2.35 days, 95% CI −3.52 to −1.17; P < .001). After this adjustment, AOFAS improvement was greater in MICA (beta = +6.40, P = .008), whereas SEFAS and VAS improvements were not statistically different. For pronation, SA achieved superior apparent correction: severe postoperative pronation (Wagner 3) was 0% after SA vs 48% after MICA, and baseline-adjusted ordered logistic regression similarly favored SA (MICA vs SA OR 3.75, 95% CI 1.08-13.03; P = .037).

Conclusion:

Both procedures reliably corrected severe HV deformity. MICA was associated with shorter total operative time and reduced length of stay. In exploratory covariate-adjusted sensitivity models, MICA maintained advantages in operative time and AOFAS scores, whereas between-group differences in SEFAS and angular radiographic outcomes were attenuated or nonsignificant. In contrast, SA demonstrated stronger correction of apparent first-metatarsal pronation, with no apparent residual severe pronation at follow-up compared with MICA.

Level of Evidence:

Level III, retrospective cohort study.

Keywords

hallux valgus scarf osteotomy minimally invasive surgery chevron and Akin pronation correction

Introduction

Hallux valgus (HV) is a complex, progressive triplanar deformity of the first ray, characterized by lateral deviation of the hallux, medial deviation and pronation of the first metatarsal, and associated soft tissue imbalances.^1,2 The clinical presentation extends beyond the cosmetic appearance of a "bunion"; patients often experience pain, difficulty with footwear, and functional limitations that can significantly impair quality of life. The prevalence of HV is substantial, affecting up to 23% of adults, with a higher incidence in women and the elderly population.^3,4

The surgical management of HV has evolved considerably over the last century. Early procedures often focused on simple bunionectomy or soft tissue correction, which frequently led to high recurrence rates because of the failure to address the underlying bony deformity. The recognition of the first metatarsal’s primary role in the deformity led to the development of various osteotomies. The open scarf osteotomy, often combined with an Akin osteotomy (scarf-Akin [SA]), has been a gold standard for moderate to severe deformities for many years. It allows for multiplanar correction—addressing varus, elevation, and pronation—and provides a large surface area for bone healing, facilitating stable internal fixation and early weight-bearing.⁵

In recent years, a paradigm shift towards minimally invasive surgery (MIS) has gained momentum across many orthopaedic subspecialties, including foot and ankle surgery. The theoretical advantages of MIS—reduced soft tissue trauma, improved cosmesis, less postoperative pain, and faster recovery—are particularly appealing to patients. The minimally invasive chevron and Akin (MICA) osteotomy represents a third-generation MIS technique that has gained widespread popularity.^2,6,7 This percutaneous procedure, performed under fluoroscopic guidance, involves an extra-articular chevron osteotomy of the metatarsal neck and a closing wedge osteotomy of the proximal phalanx (Akin). The use of cannulated screw fixation provides robust stability, distinguishing it from earlier MIS techniques that often relied on K-wires or no fixation, which had higher rates of displacement and malunion.⁶

Although numerous studies have reported excellent outcomes for both SA and MICA, there is a paucity of high-quality comparative evidence, particularly for severe deformities (HVA ≥ 40° or IMA ≥ 16°) and pronation correction. Furthermore, the understanding of the HV deformity itself has evolved, with a growing appreciation for the role of first metatarsal pronation as a critical component and a significant predictor of recurrence.^8
-10 Inadequate correction of this rotational malalignment is believed to contribute to long-term failure. Similarly, iatrogenic shortening of the first metatarsal is a known concern with any distal osteotomy, as it can alter forefoot biomechanics and potentially lead to transfer metatarsalgia.

This study was therefore designed to address a critical gap in the literature by directly comparing the outcomes of open scarf-Akin osteotomy and MICA for the treatment of severe hallux valgus in a single center in Hong Kong. The primary objectives were to compare the clinical and radiographic outcomes at 12 months postoperatively. Specifically, we aimed to evaluate differences in operative efficiency (operative time, length of hospital stay), patient-reported functional outcomes, and the ability of each technique to correct the deformity in all 3 planes, with a particular focus on the corrective power for first metatarsal pronation and the degree of resultant first metatarsal shortening. We hypothesized that MICA would offer advantages in early recovery and operative efficiency, whereas the open scarf-Akin technique would provide more robust correction of the rotational deformity.

Methods

Study Design and Patient Selection

Following institutional review board approval (Ref. CIRB-2024-457-2), a retrospective cohort study was conducted. We reviewed the medical records of all patients who underwent surgical correction for severe hallux valgus between January 2019 and January 2023 at a single institution in Hong Kong. Severe hallux valgus was defined as HVA ≥40° or IMA ≥16° (either criterion) on preoperative weight-bearing radiographs. This manuscript is reported in accordance with the STROBE guidelines.¹¹

Patients were included if they were treated with either an open scarf-Akin osteotomy (SA group) or a minimally invasive chevron and Akin osteotomy (MICA group), were at least 18 years of age, and had a minimum of 12 months of clinical and radiographic follow-up. Patients with inflammatory arthritis, neuromuscular disorders, previous first-ray surgery, or incomplete records were excluded. A total of 56 consecutive feet in 56 patients met the inclusion criteria. Thirty-three feet underwent SA (Akin osteotomy performed in all SA cases), whereas 23 feet were treated with MICA. Data were extracted from the electronic medical record and radiology archives using a standardized abstraction sheet; no imputation was performed. Complications were captured from routine consultation and follow-up clinic notes and from records of any revision surgery during the study period. Baseline weight values were retrieved from anesthesia records, and no missing weight data were present in the analyzed cohort.

Surgical Techniques

All procedures were performed by 2 senior orthopaedic surgeons experienced in both techniques. Anesthesia type and use of regional blocks for postoperative analgesia were recorded from anesthesia charts; anesthetic techniques were not standardized across cases. Estimated blood loss was extracted from the anesthesia record as documented intraoperatively; for SA cases performed under tourniquet, estimated blood loss largely reflects bleeding after tourniquet deflation.

Open scarf-Akin osteotomy

The open scarf osteotomy was performed as described by Barouk.⁵ A standard dorsomedial approach to the first metatarsal was used. A tourniquet was inflated to ensure a bloodless field. After capsulotomy, a Z-shaped osteotomy was performed in the diaphysis of the first metatarsal. The metatarsal head fragment was then translated laterally, rotated to correct pronation, and adjusted to the desired position. Any residual medial eminence/prominence was resected as needed after translation. Fixation was achieved with two 2.6-mm fully threaded Foot Motion Set (FMS) screws.

Minimally invasive chevron and Akin osteotomy

The MICA procedure performed in this study represents a third-generation MIS technique, as described by Vernois and Redfern.⁷ This approach is defined by its use of rigid screw fixation, distinguishing it from earlier minimally invasive techniques. No tourniquet was used. Under fluoroscopic guidance, a small (3-5 mm) medial incision was made over the first metatarsal neck. A Wright sideburr was used to perform a percutaneous V-shaped chevron osteotomy. The metatarsal head was then manually displaced laterally to correct the IMA (Figure 1). Any residual medial prominence could be resected using a burr after translation.¹² Fixation was achieved with 2 percutaneously placed headless compression screws (Wright MICA screws). A percutaneous Akin osteotomy was then performed using a Wright sideburr and fixed with a 3.0-mm Fixos screw. For context, “fourth-generation” minimally invasive hallux valgus procedures reflect distinct technical principles (eg, transverse extra-articular osteotomy constructs) rather than a linear hierarchy of superiority.

Figure 1.

(A) Preoperative radiograph demonstrating a severe hallux valgus deformity. (B) Immediate postoperative appearance following the MICA procedure. (C) One-year postoperative radiograph confirming maintained correction and satisfactory bony union despite the severe initial deformity.

Postoperative Protocol

The postoperative care pathway followed technique-specific standardized protocols. For the SA group, patients were kept non-weight-bearing for 2 weeks, followed by progressive weight-bearing in a surgical shoe for 4 weeks. For the MICA group, patients were allowed immediate partial weight-bearing in a surgical shoe. All patients were transitioned to regular footwear at 6-8 weeks postoperatively.

Clinical and Radiographic Evaluation

Clinical and radiographic assessments were performed preoperatively and at a minimum of 12 months postoperatively. All radiographic measurements (including Wagner pronation score, HVA, and IMA) were performed independently by 2 fellowship-trained foot-and-ankle surgeons; discrepancies were resolved by consensus. Reviewers were not blinded to surgical technique because of the visibility of distinct hardware on radiographs.

Clinical Outcomes: Clinical outcomes were evaluated using the American Orthopaedic Foot & Ankle Society (AOFAS) Forefoot Score, the Self-Reported Foot and Ankle Score (SEFAS), and the visual analog scale (VAS) for pain (0 = no pain, 10 = worst imaginable pain).

Radiographic Outcomes: Standardized weight-bearing dorsoplantar and lateral radiographs were obtained. The following parameters were measured:

● Hallux valgus angle (HVA): The angle between the longitudinal axes of the first metatarsal and the proximal phalanx.

● Intermetatarsal angle (IMA): The angle between the longitudinal axes of the first and second metatarsals.

● Distal metatarsal articular angle (DMAA): The angle between a line perpendicular to the longitudinal axis of the first metatarsal and a line along the articular surface of the metatarsal head.

● First metatarsal shortening: The change in length of the first metatarsal, measured from the base to the center of the head on dorsoplantar radiographs.

● First metatarsal pronation: Pronation was assessed using the lateral metatarsal head shape (Wagner/Okuda) method on dorsoplantar radiographs, which scores the shape of the lateral metatarsal head from 1 (no pronation) to 3 (severe pronation).^8,9 (Figure 2).

Figure 2.

(A) The Wagner method depicting a score of 1 (angular, distance > 2 mm, indicating no pronation). (B) Intermediate Wagner score of 2 (1 mm < distance ≤ 2 mm, indicating moderate pronation). (C) Rounded contour corresponding to Wagner score 3 (distance ≤ 1 mm, indicating severe pronation). An imaginary circle is fitted to the articular surface of the first metatarsal head, and the score is defined by the maximum distance between this circle and the lateral cortical edge.

Statistical Analysis

Statistical analyses were performed using IBM SPSS Statistics (version 28.0; IBM Corp). Continuous variables are reported as median [Q1, Q3] for nonparametric distributions and mean (95% CI) for approximately normal distributions; group comparisons used independent t tests for approximately normal distributions and Mann-Whitney U tests otherwise. Categorical variables were presented as counts and percentages and were compared using χ² tests or Fisher exact tests when expected cell counts were small. Because the cohort was not powered for stable multivariable modeling across multiple outcomes, primary between-group comparisons are presented as unadjusted analyses. To address potential baseline deformity imbalance for angular endpoints, baseline-adjusted linear regression models were fitted for postoperative HVA, IMA, and DMAA using postoperative angle as the dependent variable and procedure group (MICA vs SA) plus the corresponding preoperative angle as covariates. As a limited sensitivity analysis for potential confounding by concomitant procedures, 2-predictor linear regression models were fitted for selected continuous outcomes with selected continuous outcomes as dependent variables and procedure group (MICA vs SA) plus concomitant lesser-toe procedure (yes/no) as covariates (Table 3). Procedure-group coefficients are reported as MICA minus SA for consistency with the logistic model (SA reference). Regression coefficients are reported as adjusted mean differences with 95% CIs and 2-sided P values derived from model-based SEs (Wald/t tests). Because Wagner pronation is an ordinal endpoint (1 to 3), it was summarized as category counts and percentages (not means or mean ± SD), and postoperative pronation was analyzed using baseline-adjusted ordered logistic regression (postoperative pronation ~ group + preoperative pronation), with Mann-Whitney U as a supportive nonparametric comparison. Severe pronation (Wagner 3 vs 1-2) was additionally summarized descriptively and compared using Fisher exact test. A P <.05 was considered statistically significant.

Results

Patient Characteristics

Fifty-six consecutive feet (SA, n = 33; MICA, n = 23) were analyzed. Baseline demographics were broadly comparable; preoperative HVA, IMA, and DMAA were numerically higher in MICA but not statistically different between groups (P = .072, P = .098, and P = .133, respectively; Table 1). Preoperative Wagner pronation category distribution was also numerically more severe in MICA but not significant (P = .094). Concomitant lesser-toe procedures were numerically more frequent in SA (85% vs 61%; P = .056), but this difference did not reach statistical significance. Complete baseline data are summarized in Table 1.

Table 1.

Baseline Patient Demographics and Preoperative Radiographic Measurements.^a

Metric	SA Group (n = 33)	MICA Group (n = 23)	P-value
Age, y	64.0 [52.0, 69.0]	68.0 [60.5, 71.5]	.279
Sex, female, n (%)	27 (82)	19 (83)	1.000
Weight, kg	58.4 [50.3, 62.6]	58.0 [49.3, 65.1]	.796
Diabetes mellitus, n (%)	3 (9.1)	2 (8.7)	.999
Pre-op HVA, degrees	38.5 (34.0-43.0)	47.4 (43.0-51.0)	.072
Pre-op IMA, degrees	15.9 (14.1-17.6)	18.1 (15.8-20.4)	.098
Pre-op DMAA, degrees	14.4 (12.4-16.4)	20.7 (14.7-26.8)	.133
1st MT length (mm)	62.4 [58.1, 65.3]	65.3 [59.0, 67.2]	.267
Pre-op pronation: Wagner 1/2/3, n (%)	6 (18) / 13 (39) / 14 (42)	2 (9) / 6 (26) / 15 (65)	.094
Lesser toe surgery, n (%)	28 (85)	14 (61)	.056

Abbreviations: DMAA, distal metatarsal articular angle; 1st MT, first metatarsal; HVA, hallux valgus angle; IMA, intermetatarsal angle; MICA, minimally invasive chevron and Akin; SA, scarf-Akin.

Values are reported as median [Q1, Q3] or mean (lower to upper 95% CI) as indicated by formatting. Wagner pronation categories are reported as n (%).

Primary Endpoints

Postoperative angular correction (HVA, IMA). Both procedures achieved substantial coronal correction with no between-group differences at 12 months on unadjusted comparisons (postoperative HVA: P = .502; postoperative IMA: P = .618; Table 2). To address baseline deformity imbalance, baseline-adjusted linear regression (post angle ~ group + pre angle) showed no between-group differences (HVA: beta = 0.84 deg, 95% CI −4.59 to 6.27; P = .761; IMA: beta = 0.01 deg, 95% CI −2.99 to 3.01; P = .994). Baseline-adjusted DMAA similarly showed no between-group difference (beta = −0.01 deg, 95% CI −2.81 to 2.79; P = .994).

Table 2.

Comparison of Operative, Clinical, and Radiographic Outcomes at 12 Months.^a

Metric	SA Group (n = 33)	MICA Group (n = 23)	P Value
Operative time, min	178.0 [145.0, 220.0]	141.0 [113.5, 170.0]	.002
Length of stay, d	4.1 [3.3, 5.0]	1.7 [0.9, 2.5]	<.001
Blood loss, mL	20.0 [0.0, 50.0]	50.0 [0.0, 50.0]	.175
AOFAS improvement	11.0 (8.8-13.2)	17.6 (13.5-21.7)	.006
SEFAS improvement	7.3 (5.4-9.1)	11.8 (10.7-13.0)	.032
VAS improvement	3.0 [3.0, 4.0]	3.0 [2.0, 4.0]	.822
Radiographic outcomes, degrees
Post-op HVA	14.0 (8.0-21.0)	16.0 (10.5-23.5)	.502
Post-op IMA	7.0 (5.0-9.0)	8.0 (4.0-11.0)	.618
Post-op DMAA	7.2 (5.8-8.7)	8.3 (5.4-11.1)	.513
Post-op pronation: Wagner 1/2/3, n (%)	5 (15%) / 28 (85%) / 0 (0%)	5 (22%) / 7 (30%) / 11 (48%)	.013
Severe pronation: Wagner 3, n (%)	0 (0%)	11 (48%)	<.001
Baseline-adjusted ordered logistic regression for postoperative pronation category: Wagner 1-3, OR for MICA vs SA (95% CI)	Reference	3.75 (1.08-13.03)	.037
1st MT shortening, mm	3.8 (2.0-5.6)	6.4 (4.4-8.5)	.049

Abbreviations: AOFAS, American Orthopaedic Foot & Ankle Society score; DMAA, distal metatarsal articular angle; HVA, hallux valgus angle; IMA, intermetatarsal angle; MICA, minimally invasive chevron and Akin; 1st MT, first metatarsal; SA, scarf-Akin; SEFAS, Self-Reported Foot and Ankle Score; VAS, visual analog scale.

Values are reported as median [Q1, Q3] or mean (lower to upper 95% CI) as indicated by formatting. Wagner pronation categories are reported as n (%). Unless otherwise specified, P values reflect unadjusted between-group comparisons. The ordered logistic regression row reports the baseline-adjusted odds ratio (OR) for being in a higher (worse) postoperative pronation category (Wagner 1-3) comparing MICA with SA (SA reference), adjusted for preoperative pronation.

Patient-reported clinical outcomes

Unadjusted improvements favored MICA for AOFAS and SEFAS (P = .006 and P = .032; Table 2), whereas unadjusted VAS pain improvement was similar (P = .822). In sensitivity regression models adjusting for concomitant lesser-toe procedures (Table 3), AOFAS improvement was higher in MICA (beta = +6.40 points, 95% CI 1.67 to 11.13; P = .008), whereas SEFAS and VAS improvements were not statistically different after adjustment (beta = +2.68, P = .064; and beta = +0.12, P = .713).

Table 3.

Exploratory 2-Predictor Linear Regression Models Adjusting for Concomitant Lesser-Toe Procedure (Yes/No), With Procedure Effect Expressed as MICA vs SA (SA Reference).^a

Outcome	Beta (MICA vs SA)	95% CI	P Value	Beta (Lesser-toe yes)	95% CI	P Value	R²
Operative time, min	−40.0	−66.3 to −13.7	.003	+37.1	2.5 to 71.7	.036	0.22
Length of stay, d	−2.35	−3.52 to −1.17	<.001	+0.99	−0.06 to 2.03	.064	0.26
AOFAS improvement	+6.40	1.67 to 11.13	.008	−2.55	−7.48 to 2.38	.310	0.17
SEFAS improvement	+2.68	−0.15 to 5.51	.064	−1.11	−3.79 to 1.57	.418	0.07
VAS improvement	+0.12	−0.52 to 0.76	.713	−0.02	−0.65 to 0.62	.960	0.02
HVA correction (pre-post), degrees	+4.44	−2.23 to 11.11	.192	+6.75	−0.62 to 14.13	.073	0.10
IMA correction (pre-post), degrees	+1.62	−1.54 to 4.77	.315	−0.46	−3.12 to 2.20	.736	0.03
DMAA correction (pre-post), degrees	+6.22	1.01 to 11.42	.019	−0.02	−5.81 to 5.77	.994	0.12
1st MT shortening, mm	+2.91	0.20 to 5.62	.035	+2.32	−0.54 to 5.18	.112	0.12

Beta values represent adjusted mean differences. Sensitivity linear regression models included procedure group and concomitant lesser-toe procedure (yes/no). Procedure beta coefficients represent MICA minus SA, and lesser-toe coefficients represent yes minus no. These analyses are exploratory and intended as sensitivity analyses for potential confounding. R² represents the proportion of variability explained by included predictors.

First-metatarsal pronation (ordinal 1-3, Wagner) favored SA at follow-up. Postoperative categories for Wagner 1, 2, and 3, respectively, were 5, 28, and 0 for SA and 5, 7, and 11 for MICA (Mann-Whitney U, P = .013). Severe pronation (Wagner 3) was absent in SA and present in 48% of MICA cases (Fisher exact, P < .001). Baseline-adjusted ordered logistic regression favored SA for postoperative pronation category (MICA vs SA OR 3.75, 95% CI 1.08-13.03; P = .037; Table 2).

Secondary Endpoints

Operative metrics

In sensitivity regression models adjusting for concomitant lesser-toe procedures, MICA was associated with shorter operative time (beta = −40.0 min, 95% CI −66.3 to −13.7; P = .003) and shorter length of stay (beta = −2.35 days, 95% CI −3.52 to −1.17; P < .001) compared with SA (Table 3). Concomitant lesser-toe procedures were independently associated with longer operative time (+37.1 min, 95% CI 2.5-71.7; P = .036). Estimated blood loss was similar between groups (P = .175), although interpretation is limited because of tourniquet use in SA and none in MICA. Model fit is summarized by R²; for example, R² = 0.22 for operative time indicates that 22% of between-patient variation in operative time was explained by procedure group and concomitant lesser-toe status.

Radiographic outcomes

Radiographic outcomes in sensitivity models (Table 3) showed no between-group difference in HVA and IMA correction (P = .192 and P = .315). DMAA correction was greater in MICA (beta = +6.22 degrees, 95% CI 1.01-11.42; P = .019), and first-metatarsal shortening was greater in MICA (beta = +2.91 mm, 95% CI 0.20-5.62; P = .035). Postoperative DMAA remained not different in unadjusted analysis (P = .513) and on baseline-adjusted regression (post DMAA ~ group + pre DMAA; P = .994), which may reflect greater correction in MICA given its numerically higher baseline DMAA.

Complications and Follow-up

No recorded major complications including (screw irritation, delayed union, transfer metatarsalgia, numbness, wound issues) were identified in routine consultation and follow-up notes during the study period. No revision surgeries were required in either group. Detailed 12-month clinical and radiographic metrics are provided in Table 2.

A comprehensive comparison of operative metrics, patient-reported outcomes, and radiographic measurements at 12 months is presented in Table 2.

Discussion

Both techniques achieved excellent and comparable correction of HVA and IMA despite the severity of deformity treated, aligning with prospective, randomized, and matched comparative series across open scarf-Akin, distal chevron, and contemporary MIS constructs.^7,13
-20 These findings are consistent with the available comparative systematic review/meta-analysis of PECA/MICA vs scarf-Akin techniques.²¹ Guided percutaneous systems and patient-specific instrumentation may further improve technical accuracy and reproducibility in MIS hallux valgus surgery.²² Ongoing minimally invasive innovations continue to expand MIS applicability in severe cases while emphasizing multiplanar control.²³ Additionally, apparent pronation correction with PECA/MICA techniques is feasible and has been demonstrated radiographically.²⁴

Pronation analyses favored SA at follow-up: severe pronation (Wagner 3) appeared absent after SA but present in 48% after MICA. Unadjusted and baseline-adjusted ordinal analyses were consistent with superior postoperative pronation categories with SA; however, given the limited sample and event counts, these findings should be interpreted cautiously.

Interestingly, MICA demonstrated greater AOFAS improvement despite less robust radiographic pronation correction. This dissociation may reflect short-term advantages of a minimally invasive approach—reduced soft tissue disruption and facilitation of earlier rehabilitation—which can translate into better early patient- and surgeon-perceived function even when rotational radiographic endpoints are not fully normalized.^19,21 Conversely, residual first-metatarsal pronation has been associated with hallux valgus recurrence (including the lateral metatarsal head “round sign” as a recurrence risk factor), and 3D imaging studies suggest that greater pronation correction is associated with lower recurrence rates.^8,10 Given our 12-month follow-up, we cannot determine whether the observed pronation differences will translate into differential recurrence or later functional convergence/divergence; longer-term follow-up with weight-bearing CT-based rotational assessment is warranted.

Perioperative efficiency favored MICA, which reduced operative time and length of stay, mirroring the faster recovery profiles reported across minimally invasive series.^7,15
-18 In 2-predictor sensitivity models adjusting for concomitant lesser-toe procedures, MICA remained associated with shorter operative time and shorter length of stay (Table 3). Although concomitant lesser-toe surgery was more common in SA (P = .056), the difference did not reach conventional statistical significance; nevertheless, residual confounding in operative-time and length-of-stay comparisons cannot be excluded, and the current sample was not powered to rule out modest effects. Although MICA demonstrated higher estimated blood loss in our cohort, the absolute volumes remained low in both groups. Between-group blood-loss comparisons are limited by tourniquet use in SA and none in MICA; interpretation should therefore be cautious.

Another important differentiating factor was the degree of first metatarsal shortening. Our study found greater first metatarsal shortening after MICA than SA (beta = +2.91 mm; P = .035). Although no transfer metatarsalgia was reported at 12 months, continued follow-up is warranted to determine whether this difference translates into longer-term forefoot symptoms. The diaphyseal nature of SA allows for greater control over metatarsal length, whereas the geometry of the distal chevron osteotomy in MICA may lead to more shortening upon lateral translation of the capital fragment. This finding is consistent with other studies.¹⁵ As an open question for future research, the inclination of the MICA osteotomy and the burr kerf (approximately 2 mm) may influence net length change and could potentially mitigate shortening, but optimal parameters remain undefined.

This study has several strengths. It is one of the few studies to directly compare modern MICA techniques with the gold-standard scarf-Akin construct specifically in a population with severe deformities. We used multiple clinical outcome measures (AOFAS, SEFAS, and VAS), including patient-reported instruments, and performed a detailed radiographic analysis that included an assessment of pronation. However, the study is not without limitations. The retrospective design is the most significant limitation, introducing potential selection bias and temporal confounding. Baseline deformity (HVA, IMA, and DMAA) and pronation severity were numerically higher in MICA, although these differences were not statistically significant (HVA, P = .072; IMA, P = .098; DMAA, P = .133; pronation, P = .094). To address baseline deformity imbalance for angular endpoints, baseline-adjusted regression (post angle ~ group + pre angle) showed no between-group differences in postoperative HVA, IMA, and DMAA, supporting the robustness of the primary angular conclusions. Although cohort size and event counts were limited, pronation analyses (including severe pronation 0% in SA vs 48% in MICA) favored SA; these findings should be interpreted cautiously and validated in larger prospective cohorts. Although concomitant lesser-toe surgery was more common in SA (P = .056), this difference did not reach statistical significance; nevertheless, residual confounding in operative-time and length-of-stay comparisons cannot be excluded, and the current sample was not powered to rule out modest effects. A matched sensitivity analysis excluding lesser-toe procedures was not performed because subgroup sample size was insufficient for reliable inference; this was treated as a study limitation. Radiographic assessment of Wagner pronation scores was not blinded, creating potential observer bias. Additionally, no perioperative endpoints were captured (eg, immediate postoperative pain trajectory, analgesic use, early function, time to return to work), limiting conclusions regarding early recovery advantages of MIS beyond operative time and length of stay. Finally, the 12-month follow-up period is insufficient to draw definitive conclusions about long-term outcomes, particularly regarding recurrence and the clinical consequences of metatarsal shortening. The learning curve associated with MICA is well documented,²⁵ and although the surgeons were experienced, this could still be a confounding factor.

Selection between scarf-Akin (SA) and MICA for severe hallux valgus should be individualized. In this cohort, MICA showed shorter total operative time and hospital stay, but these findings should be interpreted in the context of a higher burden of concomitant lesser-toe procedures in the SA group. In exploratory covariate-adjusted sensitivity models, MICA maintained advantages in operative time and AOFAS scores, whereas between-group differences in SEFAS and angular radiographic outcomes were attenuated or nonsignificant. In contrast, SA provided superior correction of rotational deformity, with no residual severe pronation at follow-up (0% Wagner 3) compared with MICA (48%). Longer-term studies with weight-bearing CT and adequately powered designs are needed to determine whether these differences affect recurrence and forefoot symptoms over time.

Future research should focus on prospective, randomized controlled trials with larger patient cohorts and long-term follow-up to definitively compare the rates of recurrence, patient satisfaction, and the incidence of complications such as transfer metatarsalgia. The use of advanced imaging techniques, such as weight-bearing computed tomography, would also provide a more accurate and 3-dimensional assessment of bony correction, particularly for metatarsal pronation. Prospective collection of perioperative endpoints (pain, analgesic use, early function, time to return to work) and standardized complication reporting would further strengthen comparative effectiveness conclusions.

Conclusion

Both scarf-Akin (SA) and MICA achieved reliable correction of severe hallux valgus at 12 months. MICA was associated with shorter total operative time and reduced length of stay, and exploratory covariate-adjusted sensitivity models showed persistent advantages for MICA in operative time and AOFAS scores, whereas SEFAS and angular radiographic between-group differences were attenuated or nonsignificant. SA provided superior apparent pronation correction, with no apparent residual severe postoperative pronation (0% Wagner 3) compared with MICA (48%). Procedure selection should therefore weigh clinical recovery advantages of MICA against potential rotational-correction advantages of SA, and prospective adequately powered studies are warranted. Because perioperative endpoints (immediate pain trajectory, analgesic use, and return-to-work timing) were not collected, early-recovery advantages should be interpreted cautiously.

Supplemental Material

sj-pdf-1-fao-10.1177_24730114261436758 – Supplemental material for Comparison of Open Scarf-Akin Osteotomy and Minimally Invasive Chevron and Akin (MICA) Osteotomy for Severe Hallux Valgus Deformity: A Retrospective Study

Supplemental material, sj-pdf-1-fao-10.1177_24730114261436758 for Comparison of Open Scarf-Akin Osteotomy and Minimally Invasive Chevron and Akin (MICA) Osteotomy for Severe Hallux Valgus Deformity: A Retrospective Study by WaiLok Charlix Yeung, Ming Hong Chau and Ka Ki Stephanie Liu in Foot & Ankle Orthopaedics

Footnotes

ORCID iDs

WaiLok Charlix Yeung, MBBS, MRes Bioscience

Ming Hong Chau, M.B.Ch.B., F.H.K.C.O.S., F.H.K.A.M. (Ortho. Surg.), F.R.C.S.Ed. (Orth.), M.R.C.S.Ed

Ethical Considerations

Institutional review board approval: Ref. CIRB-2024-457-2

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Disclosure forms for all authors are available online.

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