Outcomes and Complications for Minimally Invasive Distal Transverse Metatarsal Osteotomy–Akin Osteotomy (MITA) for Hallux Valgus: 493 Cases

Abstract

Background

Hallux valgus is one of the most common forefoot deformity, leading to impaired mobility and reduced quality of life. Minimally invasive surgical techniques offer potential advantages, including reduced soft tissue disruption and accelerated postoperative recovery. The present study aimed to assess the clinical and radiographic outcomes of Minimally Invasive Distal Transverse Metatarsal Osteotomy combined with Akin Osteotomy (MITA) in a large patient cohort.

Methods

A retrospective review was performed on 493 feet treated with MITA between March 2020 and December 2021 at a single orthopedic center. Radiographic parameters—including hallux valgus angle (HVA), intermetatarsal angle (IMA), sesamoid position, and foot width—were evaluated preoperatively and at multiple postoperative points up to one year. Clinical outcomes were assessed by the Visual Analog Scale (VAS), the American Orthopaedic Foot & Ankle Society (AOFAS) score, and the Manchester-Oxford Foot Questionnaire (MOXFQ), including each domain. Complications were classified into three grades according to severity. Statistical analysis included paired t-tests and repeated measures using a general linear model.

Results

Significant improvements were demonstrated across all radiographic and clinical parameters. Mean HVA decreased from 34.24° to 8.38°, and IMA from 12.67° to 5.78° (p < 0.001). Cases with grade 3 sesamoid displacement decreased markedly, from 424 to 5. Clinical outcomes also improved substantially: VAS scores declined from 2.91 to 0.20, AOFAS scores increased from 82.20 to 99.11, and MOXFQ scores decreased from 36.02 to 4.39 (all p < 0.001). The majority of complications were minor (Grade 1), with transient neurapraxia being the most frequent (6.0%). Severe complications (Grade 3) were uncommon and manageable.

Conclusions

MITA provides effective correction of hallux valgus, achieving excellent radiographic alignment and favorable clinical outcomes. Its minimally invasive approach facilitates rapid postoperative recovery and is associated with a low complication profile, supporting its role as a viable alternative to conventional open procedures and previous generation MIS techniques.

Trial registration

This study was approved by the Korea National Institute for Bioethics Policy (KoNIBP) (Approval No. P01-202506–01-028). As participant data were anonymized, the study was retrospectively registered.

Background

Hallux valgus is one of the most common forefoot deformities [1]. It significantly impairs patients’ mobility and quality of life, often due to pain and difficulty wearing shoes [2, 3]. Characterized by lateral deviation of the great toe and medial displacement of the first metatarsal, the deformity can lead to pain, instability, progressive foot dysfunction, and aesthetic concerns [1, 2, 4]. Conservative treatments, including medication, orthotics, and physical therapy, provide only temporary relief and generally fail to correct the underlying structural deformity [5]. Surgical intervention therefore remains the definitive treatment for advanced cases [3, 6]. More than 150 surgical techniques have been described, differing in osteotomy site, fixation method, and soft tissue management [6–10]. Recently, minimally invasive surgery for hallux valgus has been introduced [11–13]. Several studies recommend this approach over conventional open surgery because reduced soft tissue disruption facilitates faster postoperative recovery [14, 15]. In addition, shorter operative times and earlier discharge may further benefit patients [16].

Among the minimally invasive surgeries, the Minimally Invasive Distal Transverse Metatarsal Osteotomy–Akin Osteotomy (MITA) has emerged as a promising option for hallux valgus correction. MITA is designed to realign the first metatarsal, correct the deformity, and restore foot function, while minimizing soft tissue injuries during surgery.

Introduction

Distal chevron osteotomy has been proven effective in open surgical procedures and continues to be widely performed [17]. Moreover, this technique has also been adopted in third-generation minimally invasive surgery. The third generation of minimally invasive surgery for hallux valgus correction involves a Chevron osteotomy for metatarsal realignment and internal fixation using two parallel screws, as implemented in techniques such as MICA (Minimally Invasive Chevron and Akin osteotomies) and PECA (Percutaneous Chevron and Akin). The fourth generation employs a transverse osteotomy at the extra-articular site of the metatarsal bone, fixed with two fully threaded screws. Owing to differences in osteotomy and fixation methods, the fourth generation provides improved efficacy in rotational deformity correction and biomechanical stability compared with the third generation [18].

Previous studies on the advancement of minimally invasive surgery (MIS) for hallux valgus have advanced to the fourth generation [19]. However, they are limited by short follow-up durations and relatively small sample sizes. Since 2020, our institution has been performing MITA surgery. This study retrospectively analyzed the radiographic and clinical outcomes of cases who underwent MITA surgery with a minimum follow-up over one year in order to evaluate its effectiveness with regard to radiological correction, pain relief, functional and social improvement, and postoperative complications.

Materials and Methods

Materials: Inclusion& Exclusion (Fig. 1)

Fig. 1.

Flowchart of foot selection for the study. Of the 995 feet undergoing primary MITA surgery in patients older than 16 years between March 2020 and December 2021, 502 feet were excluded (follow-up < 1 year, n = 489; additional surgery, n = 13), resulting in 493 feet included in the analysis

This retrospective study included data from one institution, SNU Seoul Hospital. Initially, 995 feet that underwent primary hallux valgus correction using MITA surgery between March 2020 and December 2021 were considered. Patients were included if they experienced bunion pain with a moderate or greater hallux valgus angle and Intermetatarsal angle or if they reported functional or social discomfort due to hallux valgus deformity despite the absence of pain and sought surgical correction. In addition, only patients older than 16 years old were included. A total of 489 feet were excluded because the follow-up period was less than one year, and 13feet were excluded due to concomitant procedures such as midfoot fusion, flatfoot correction, or ankle surgery. Finally, 493 feet were included in the analysis.

Surgical Method and Postoperative Management

Under C-arm fluoroscopic guidance, a 2-mm stab incision was created at the proximal one-third of the medial aspect of the first metatarsal. The periosteum was carefully elevated using a freer elevator. A distal transverse osteotomy was then performed with a Shannon burr. The proximal fragment of the metatarsal was displaced medially by inserting a sharp freer elevator into the intramedullary space of the proximal fragment of the first metatarsal bone. The rotational deformity was subsequently corrected manually. After confirming the correction under C-arm fluoroscopy, fixation was achieved percutaneously using two 3.5-mm headless cannulated screws (Montblanc Screw System, manufactured by River Field Medical Co., Ltd.). A medial eminence resection (bumpectomy) was performed on the medial aspect of the first metatarsal using a wedge burr and an SSG bunion rasp. The SSG Bunion Rasp, developed by Dr. Seo, is a device connected to Styker TPX system (Fig. 2) It has a raspatory head with automatically oscillation, allowing for a more efficient and aggressive bumpectomy.

Fig. 2.

SSG bunion rasp developed by Dr. Seo for effective bumpectomy

Subsequently, a second 2-mm stab incision was created at the medial base of the first proximal phalanx. After subperiosteal dissection with a freer elevator, an osteotomy was performed using a Shannon burr. The osteotomy site was then manually closed to achieve the desired alignment and fixed with a single 3.0-mm headless cannulated screw (Montblanc Screw System, manufactured by River Field Medical Co., Ltd.).

Postoperatively, patients wore a postoperative shoe with an inflexible outsole that functions as a splint for the first four weeks, and they were allowed to ambulate as tolerated during this period. Once the wound had healed, typically around two weeks, patients began using a postoperative corrective soft orthosis, Hallu Care (Fig. 3) which is made of elastic fabric and applies varus-directed traction to the big toe; use of the orthosis was continued until six weeks postoperatively.

Fig. 3.

Hallu Care orthotic device worn for 6 weeks postoperatively. A medial band on the first toe applies a varus-directed pull to main tain corrected alignment

Postoperatively, screw removal was routinely performed between three and four months after surgery to prevent irritation and to facilitate any potential additional surgical procedures that might be required, such as in cases of subsequent trauma (Fig. 4).

Fig. 4.

Serial foot X-rays of a patient. A Preoperative weight-bearing anteroposterior (AP) view, B Immediate postoperative weight-bearing AP view, and C Weight-bearing AP view four month after surgery, following screw removal

Observation indicators

Data used to evaluate the outcomes of MITA surgery included both radiographic parameters and subjective assessment scales. Radiographic parameters included hallux valgus angle (HVA), intermetatarsal angle (IMA), sesamoid bone position, and bone foot width. The HVA was defined as the angle between the long axis of the first metatarsal bone and that of the first proximal phalanx. The IMA was defined as the angle between the long axis of the first and second metatarsal bones (Fig. 5).

Fig. 5.

Radiographic measurements of the foot: A Hallux valgus angle, B intermetatarsal angle, and C bony foot width

Traditionally, the sesamoid position was evaluated by the Hardy and Clapham classification [20]. In this study, the classification was modified and grouped as follows: I and II as Grade 0, III and IV as Grade 1, V and VI as Grade 3, and VII as Grade 4.(Fig. 6) This reclassification facilitated a simplified and more flexible statistical comparison. Specifically, it was classified as Grade 0 when the sesamoid remained on the medial side to the axis; Grade 1 when less than 50% of the sesamoid extended laterally beyond the axis; Grade 2 when more than 50% extended laterally beyond the axis; and Grade 3 when the entire sesamoid was located lateral to the axis.

Fig. 6.

Radiographic grading of sesamoid bone position. Blue ovals indicate the medial sesamoid bone, and red lines denote the axis of the first metatarsal bone. A Grade 0, B Grade 1, C Grade 2, and D Grade 3

Bone foot width was measured as the distance between the most medial point of the first metatarsal head and the most lateral point of the fifth metatarsal head. All of the radiographic measurements were collected serially; HVA and IMA were measured preoperatively, and at 1 month, 2 months, and 1 year postoperatively; Sesamoid bone position and bony foot width were assessed preoperatively, and at 6 months, and 1 year postoperatively.

The assessment scales included the Visual Analog Scale (VAS) for pain, the American Orthopedic Foot and Ankle Society (AOFAS) score for function, and the Manchester-Oxford Foot Questionnaire (MOXFQ). The MOXFQ consists of three separate domains, the pain domain, the walking and standing domain, and the social domain. Each domain scale was analyzed independently to assess improvements following MITA surgery.

Postoperative complications were categorized into three severity grades based on their clinical significance [21–23]. Grade 1 complications were defined as adverse events with minimal clinical relevance that did not cause any deviation from routine postoperative follow-up. Grade 2 complications were defined as events that were treatable but did not require additional surgical intervention or unplanned hospital admission. Grade 3 complications were defined as events that were treatable but require surgical intervention or an unplanned hospital admission.

Statistical Analysis

Statistical analysis was performed using SPSS software (version 27.0; IBM Corp., Armonk, NY, USA). Continuous data on each foot were collected and analyzed using a paired t-test and repeated measures using the general linear model.

Results

A total of 493 feet were included in this study, comprising 243 right feet and 250 left feet. Female patients’ feet accounted for 429(87.01%). The mean age at the time of MITA surgery was 56.32 years, ranging from 17 to 84 years. The mean body mass index (BMI) was 23.32 kg/m2. The mean follow-up duration was 17.96 months, with the longest follow-up extending to 54 months (Table 1).

Table 1.

Demographic and clinical characteristics of the study population (n = 493)

n = 493	Average (range)	Standard Deviation
Age(year)	56.32 (17–84)	13.17
BMI(kg/m2)	23.32 (15.62–44.96)	3.41
Follow up(months)	17.96 (12–54)	9.41

	Number	Rate
Sex
Male	64	12.98%
Female	429	87.01%
Side
Right	243	49.29%
Left	250	50.70%

Continuous variables (age, body mass index [BMI], and follow-up duration) are presented as mean ± standard deviation (range). Categorical variables (sex and affected side) are presented as number and rate (percentage)

Radiographic improvements following MITA surgery (Fig. 7)

Fig. 7.

Serial change in key radiographic parameters following surgery. Four line graphs depict measurements at defined time points: A Hallux Valgus Angle, B Inter-Metatarsal Angle (IMA), C Sesamoid Position Grade, D Foot Bone Width

The results demonstrated statistically significant improvements in radiographic parameters. Themean hallux valgus angle(HVA) decreased from 34.24° preoperatively to 8.38° at one year postoperatively(Standard Deviation 7.17, p-value < 0.001). Similarly, the mean intermetatarsal angle(IMA) decreased from 12.67° preoperatively to 5.78° at one year postoperatively(Standard Deviation 4.17, p-value < 0.001) (Table 2).

Table 2.

Radiographic parameters and sesamoid position before and after surgery (n = 493)

	PreOperative	PostOperative 1 month	Post Operative 2 months	PostOperative 1 year	p-value
Hallux Valgus Angle	34.24°	9.58°	8.84°	8.38°	< 0.001
InterMetatarsal Angle	12.67°	6.14°	6.20°	5.78°	< 0.001

	PreOperative	PostOperative 6 months	PostOperative 1 year	p-value
Foot Bone Width	98.49 mm	87.71 mm	88.58 mm	< 0.001
Sesamoid position	Grade 3 424 patients	11 patients	5patients
	Grade 2 60 patients	171 patients	73 patients	< 0.05
	Grade 1 7 patients	133 patients	159 patients
	Grade 0 2 patients	178 patients	256 patients

Continuous variables (hallus valgus angle, intermetatarsal angle and foot bone width) are presented as mean ± standard deviation. Sesamoid position is presented as number of patients in each grade

For both HVA and IMA, the values showed a progressive decrease across the measured periods, with the exception of IMA between 1 and 2 months. In HVA, the most pronounced decrease occurred between the preoperative and 1-month postoperative. (p-value < 0.001). Additional but smaller decreases were observed between 1 and 2 months (p-value = 0.011) and between 2 months and 1 year (p-value < 0.001). For IMA, the most significant decrease was noted between preoperative to 1-month postoperative(p-value < 0.001). Also, the difference between 2 months and 1 year remained statistically decreasing (p-value < 0.001). However, a slight increase in IMA was observed between 1 and 2 months(p-value = 0.008), albeit a minor increase,0.06° (Table 3).

Table 3.

Differences in hallux valgus angle and intermetatarsal angle between consecutive measurement intervals

	PreOperative—PostOperative 1 months	p-value	PostOperative 1 month—PostOperative 2 months	p-value	Post Operative 2 months—PostOperative 1 year	p-value
Hallux Valgus Angle	24.66	< 0.001	0.74	< 0.001	0.45	< 0.001
InterMetatarsal Angle	6.53	< 0.001	-0.06	< 0.001	0.42	< 0.001

Mean angular changes are shown for preoperatives versus 1-moth postoperative, 1-month versus 2-month postoperative, and 2-month postoperative versus 1-years postoperative periods

Foot width was assessed preoperatively, at 6 months postoperatively, and 1 year postoperatively. At the first follow-up, 6 months postoperatively, a statistically significant decrease was observed. However, between 6 months and 1 year, foot width increased slightly from 87.71 mm to 88.58 mm. (p-value < 0.001)(Table 1). Quantitative analysis demonstrated a mean decrease of 10.78 mm from the preoperative baseline to 6 months postoperatively (p-value < 0.001). In contrast, a modest but statistically significant increase of 0.87 mm was observed between 6 months and 1 year postoperatively (-value < 0.001) (Table 4).

Table 4.

Differences in foot bone width and sesamoid position grade between consecutive measurement intervals

Foot width	PreOperative—PostOperative 6 months	p-value	PostOperative 6 months—PostOperative 1 year	p-value
Sesamoid Position Grade	10.78	< 0.001	-0.87	< 0.001
	1.81	< 0.001	0.38	< 0.001

Mean differences are presented for preoperative versus 6-month postoperative, and 6-month versus 1-year postoperative intervals

The position of the sesamoid bone significantly improved following MITA surgery. Preoperatively, 424 cases were classified as grade 3, 60 as Grade 2, 7 as Grade 1, and 2 cases as Grade 0. At 1 year postoperatively, only 5 cases remained in Grade 3, while 73 were classified as Grade 2, 159 as grade 1, and 256 as grade 0. These serial changes were statistically significant (p-value < 0.05). These findings suggest that MITA surgery may facilitate sesamoid bone realignment, although further studies are needed to determine its isolated effect. (Table 1) With respect to changes in sesamoid position grade, the mean improvement from preoperative baseline to 6 months postoperatively was 1.81(p-value < 0.001), with an additional improvement of 0.38 observed between 6 months and 1 year (p-value < 0.001) (Table 4).

Score improvements following MITA Surgery (Fig. 8)

Fig. 8.

Serial changes in key clinical parameters following bunion surgery. Six line graphs depict measurements at defined time points: A Visual Analogue Sclae (VAS), B American Orthopaedic foot Ankle Society Score (AOFAS), C Manchester-Oxford Foot Questionnaire (MOXFQ) Total Score, D MOXFQ Pain Domain, E MOXFQ Walking & Stading Domain, F MOXFQ Social Domain

Postoperative scales showed statistically significant improvements, indicating meaningful clinical benefit. The mean Visual Analogue Scale (VAS) score decreased from 2.91 preoperatively to 0.20 at 1 year postoperatively (Standard Deviation 1.49, p-value < 0.001). The mean American Orthopedic Foot and Ankle Society (AOFAS) score increased from 82.20 preoperatively to 99.11 at 1 year postoperatively (Standard Deviation 10.04, p-value < 0.001). (Table 5).

Table 5.

Changes in painent-reposted outcome scores between preoperative, 1-month, 2-month, and 1-year postoperative evaluations

	PreOperative	PostOperative 1 month	PostOperative 2 months	PostOperative 1 year	p-value
Visual Analogue Scale(VSA) Score	2.91	2.78	0.84	0.2	< 0.001
the American Orthopaedic Foot & Ankle Society (AOFAS) score	82.2	83.01	96.67	99.1	< 0.001
Manchester-Oxford Foot Questionnaire (MOXFQ) score	36.02	30.84	8.53	4.39	< 0.001
MOXFQ pain domain score	44.61	43.86	17.72	11.79	< 0.001
MOXFQ walking&standing domain score	35.5	25.55	6.92	4.4	< 0.001
MOXFQ social domain score	41.02	36.94	11.05	7.32	< 0.001

Mean Visual analogue scale (VAS) pain score, American Orthopaedic Foot & Ankle Society (AOFAS) score, Manchester-Oxfored Foot Questionnaire (MOXFQ) over score, and MOXFQ pain, walking & standing, and social domain score are presented

There was no significant change in the VAS score between the preoperative period and 1 month postoperatively (mean difference = 0.13, p-value = 0.118). However, significant decreases were observed between 1 and 2 months (mean difference = 1.94, p-value < 0.001) and between 2 months and 1 year (mean difference = 0.64, p-value < 0.001). Similarly, the AOFAS score did not differ significantly between the preoperative period and 1 month postoperatively (mean difference = –0.81, p-value = 0.13), but significant improvements were observed between 1 and 2 months (mean difference = 13.66, p-value < 0.001) and between 2 months and 1 year (mean difference = 2.43, p-value < 0.001). (Table 6).

Table 6.

Differences in patient reported outcome scores between preoperative to 1 month, 1-month to 2 month, and 2 month to 1-year postoperative intervals. Mean changes in Visual Analogue Scale (VAS) pain score, American Orthopaedic Foot & Ankle Society (AOIAS) score, Manchester Oxford Foot Questionnaire (MOXQ) overall score, and MOXIQ pain, walking & standing, and social domain scores are presermind

	PreOperative—PostOperative 1 month	p-value	PostOperative 1 months—PostOperative 2 months	p-value	PostOperative 2 months—PostOperative 1 year	p-value
VAS score	0.13	0.118	1.94	< 0.001	0.64	< 0.001
AOFAS score	-0.81	0.13	-13.66	< 0.001	-2.43	< 0.001
MOXFQ score	5.18	< 0.001	22.31	< 0.001	4.14	< 0.001
MOXFQ-pain	0.75	0.521	26.14	< 0.001	5.93	< 0.001
MOXFQ-walking&standing	9.95	< 0.001	18.63	< 0.001	2.52	< 0.001
MOXFQ-social	4.08	0.002	25.89	< 0.001	3.73	< 0.001

Additionally, the Manchester-Oxford Foot Questionnaire (MOXFQ) score demonstrated an overall reduction from 36.02 preoperatively to 4.39 at 1 year postoperatively. (Standard Deviation 18.55, p-value < 0.001) Within the MOXFQ domains, the pain domain improved from 44.61 to 11.79(Standard Deviation 21.99, p-value < 0.001), the walking and standing domain from 35.50 to 4.40(Standard Deviation 16.79, p-value < 0.001), and the social domain from 41.02 to 7.32(Standard Deviation 23.77, p-value < 0.001), all demonstrating statistically significant improvements (p-value < 0.001). (Table 5).

The total MOXFQ score showed sequential reductions between the preoperative and 1-month postoperative periods (mean difference = 5.18, p-value < 0.001), between 1and 2 months(mean difference = 22.31, p-value < 0.001), and between 2months and 1 year periods (mean difference = 4.14, p-value < 0.001). In the each domain analysis, pain improved significantly between 1 and 2 months (mean difference = 26.14, p-value < 0.001) and again between 2 months and 1 year (mean difference = 5.93, p-value < 0.001), whereas no significant change was observed in the initial interval (p-value = 0.521). The walking and standing domain showed statistically significant improvements across all intervals (mean differences = 9.95, 18.63, and 2.52; all p-values < 0.001). Likewise, the social interaction domain improved significantly during all evaluated periods (mean differences of 4.08, 25.89, and 3.73; all p-values ≤ 0.002). (Table 6).

Complications observed following MITA Surgery (Table 7)

Table 7.

Postoperative complications stratified by severity grade

	Number of cases (foot)	Rate of cases (%)
Grade 1 complications
Delayed Wound healing	13	2.60%
Superficial cellulitis	7	1.40%
Transient neurapraxia	30	6.00%
FHL tendon injury	0	0.00%
Grade 2 complications
Additional intraoperative fixation	2	0.40%
Symptomatic osteotomy site displacement	8	1.60%
Symptomatic delayed Union	3	0.60%
Transfer metatarsalgia	28	5.60%
Intraoperative conversion to open surgery	0	0.00%
Symptomatic recurrence of HV deformity	3	0.60%
Grade 3 complications
Screw failure (fracture/screwcutout/prominent)	3	0.60%
Prominent bone	12	2.40%
Scar revision	2	0.40%
Deep infection requiring surgery	0	0.00%
Hallux varus	13	2.60%
1st MTP OA	1	0.20%
Stiffness	7	1.40%
All screw-removal rate	456	92.30%

Postoperative complications stratified by severity grade. Number of cases and rate (%) are provided for each complication type within Grade 1 (minor), Grade 2 (moderate), and Grade 3 (severe) categories. The grading of complications followed the Clavien-Dindo-Sink complication classification [21–23]

Among Grade 1 complications, the most frequent was transient neurapraxia, which occurred in 30 cases (6.0%). Delayed wound healing was observed in 13 cases (2.6%), and superficial cellulitis was observed in 7 cases (1.4%). No cases of flexor hallucis longus (FHL) tendon injury were reported. Most Grade 1 complications were successfully managed with conservative treatment, including oral medications.

Among Grade 2 complications, transfer metatarsalgia was the most common, occurring in 28 cases (5.6%). Most of these patients were managed effectively with analgesic medication and insoles; however, 7 cases (1.4%) required additional surgical intervention, such as a Weil osteotomy. Other complications included the need for additional intraoperative fixation in 2 cases (0.4%), symptomatic osteotomy site displacement in 8 cases (1.6%), symptomatic delayed union in 3 cases (0.6%), and symptomatic recurrence of hallux valgus in 3 cases (0.6%). Importantly, no cases required conversion to open surgery.

In terms of Grade 3 complications, prominent bone formation was observed in 12 cases (2.4%), scar revision was required in 2 cases (0.4%), and first metatarsophalangeal (MTP) joint stiffness occurred in 7 cases (1.4%). Screw failure, including fracture, cutout, or prominence was identified in 3 cases (0.6%). Only 1 case (0.2%) developed first metatarsophalangeal osteoarthritis (MTP OA), and no cases of deep infection were reported. Hallux varus occurred in 13 cases (2.6%), all of which required corrective surgery with an Akin procedure. Screw removal was routinely performed in most cases, except for 38 cases (7.7%).

Discussion

Minimally invasive surgery has progressively evolved, with hallux valgus correction procedures now classified as the fourth generation techniques [11–15, 18, 19, 24–26]. The MITA technique performed in our institution is derived from this latest generation and has demonstrated favorable radiographic and clinical outcomes.

According to prior systematic reviews about MICA surgery, the average postoperative reduction of the hallux valgus angle (HVA) has been reported as 20.1° ± 4.2° and the intermetatarsal angle (IMA) shows a decrease of 7.8° ± 2.1° [24]. In this study, the mean HVA reduction was 25.86°, yielding outcomes comparable to or exceeding those reported in previous MICA studies. Similarly, the IMA decreased by 6.89°, demonstrating consistent and stable correction in line with earlier reports. Notably, the extent of HVA correction surpassed that described in some prior studies, suggesting that MITA provides adequate deformity correction and maintains postoperative alignment.

The ability to simultaneously correct metatarsal rotational deformity through a transverse osteotomy appeared to contribute to significant improvement in sesamoid position. Not only was substantial realignment observed immediately postoperatively, but additional improvement was documented at the 1 year postoperatively compared with the 6 months postoperatively. These progressive changes suggest that sesamoid repositioning is not solely a byproduct of angular correction but also reflects biomechanical restoration of alignment. Given that sesamoid malposition has been identified as a key factor associated with recurrence, this continued improvement may be attributed to the enhanced rotational control and pressure redistribution afforded by the MITA surgery [27]. Importantly, such sequential enhancement between 6 months and 1 year supports the potential for long-term structural stability with this procedure.

According to a recent study, a reduction in bony foot width has also been reported [28]. In this study, bony foot width decreased by 10.06% between preoperative baseline and 1 year postoperatively. Although a significant reduction was observed following surgery, a slight increase was noted between 6 months and 1 year, rising from 87.71 mm to 88.58 mm. This minor difference—approximately 0.87 mm—was not considered clinically relevant. It is attributable not to relapse of alignment but rather to the functional restoration of weight-bearing and plantar pressure distribution. Furthermore, the initial decrease in bony foot width may reflect mechanical narrowing secondary to osteotomy, normalization of joint alignment, and subsequent soft tissues remodeling. The slight increase between 6 months and 1 year postoperatively may indicate a return to physiological weight-bearing loads on the postoperative foot, facilitated by pain relief and compensation of correction. These finding suggests that postoperative foot architecture undergoes dynamic refinement as patients progressively regain function.

Regarding scale improvements, a notable inflection point occurred between 1 and 2 months postoperatively. During this interval, the VAS score decreased by an average of 1.94 (p-value < 0.001), the total MOXFQ score improved by 22.31 (p-value < 0.001), and the pain domain alone demonstrated a 26.14 point reduction (p-value < 0.001). At the same time, the AOFAS score increased by 13.66 (p-value < 0.001). Although only limited progress was observed at the 1-month follow-up, rapid improvements in pain and function became evident from 2 months postoperatively, highlighting this period as a pivotal stage in the postoperative course.

These patterns coincide with ongoing recovery and the stabilization of corrected bony alignment. During this period, the walking and standing domain and the social domain of the MOXFQ also demonstrated significant improvement. Collectively, MITA surgery represents a viable surgical option for correction of hallux valgus, facilitating accelerated functional recovery, enhancing patient-reported satisfaction, and improving overall quality of life.

According to a recent study, MICA surgeries have demonstrated significant functional improvement, with AOFAS scores increasing from 48.2 to 95.6 and MOXFQ scores decreasing from 57.6 to 6.7 [25]. Another prospective study reported reductions in MOXFQ domain scores, with pain domain decreasing from 44.5 to 9.4, walking and standing domain from 38.7 to 6.5, and social domain from 48.0 to 6.6 [26]. The present study, which included a larger cohort than prior reports, revealed statistically significant improvements across all scales. These findings demonstrate comparable or superior outcomes, particularly with respect to pain reduction and near-maximal functional restoration. The substantial reduction in MOXFQ score—exceeding 30 points within 1 year—further reinforces the clinical value of MITA in achieving both rapid and durable postoperative recovery.

The overall complication rate following MITA surgery was low, and the most adverse events were minor and self-limiting. Grade 1 complications, such as transient neurapraxia (6.0%) and delayed wound healing (2.6%), were successfully managed conservatively without the need for surgical intervention. These rates are consistent with previously published reports regarding to MICA surgery, in which minor complications such as paresthesia and wound-related issues ranged from 5 to 10% [25]. The relatively low incidence of complications requiring reoperation—1.4% for surgical management of metatarsalgia, 2.6% for hallux varus correction—underscores the technical reproducibility and safety of the MITA procedure when performed in a controlled and experienced surgical setting. Importantly, because the second metatarsal bone was already relatively long in patients who lateral underwent surgical management for metatarsalgia, these reoperations cannot be attributed solely to the MITA surgery.

Furthermore, when compared with a prospective cohort study reporting screw-related complications in 3.9% of cases and joint stiffness in 2.1% after MICA, the present study demonstrated comparable or lower rates, with screw failure observed in only 0.6% and MTP joint stiffness in 1.4% [29]. Collectively, these findings suggest that the MITA surgery can achieve low morbidity rates while maintaining the benefits of minimally invasive surgery, including reduced surgical soft tissue trauma and accelerated recovery.

Additionally, routine screw removal was performed in most patients, primarily to prevent hardware irritation. This practice reflects, in part, cultural preferences in Korea, where many patients are reluctant to retain implants and often request their removal, a pattern that has also been common following conventional open hallux valgus correction surgeries. While implant removal was routinely performed, patients who preferred to retain the screws were allowed to do so. Additionally, in our surgical technique, bunion resection was performed, which may contribute to some degree of immediate postoperative stiffness; screw removal and subsequent brisement can therefore be beneficial. Moreover, routine implant removal provides the opportunity to address other minor procedures, such as Weil osteotomy or bunionette correction, if needed during follow-up.

Some cases of recurrence deformity or failed correction of hallux valgus may require necessary revision surgeries. The open technique for the correction of hallux valgus can be the solution for such cases [30]. Further research is warranted to evaluate the effectiveness of revision surgery using the MITA technique in such cases.

Limitations

This study has some limitations. First, its retrospective design inherently carries risks of selection bias and limits the ability to establish causal relationships. Second the study cohort was relatively homogeneous with respect to ethnicity, age, and body mass index(BMI), all of which may restrict the generalizability of our findings. Because nearly all patients were of East Asian descent and had BMIs within a narrow range, it remains unclear whether similar radiographic and clinical outcomes would be observed in Western populations or patients with obesity. Future multicenter studies including more diverse demographic groups are warranted to confirm the external validity of MITA across border patient populations.

As most hallux valgus surgeries at our institution are performed using minimally invasive techniques, it was not feasible to establish a direct comparison group of open procedures performed by the same surgeon and under comparable institutional protocols. This limitation restricted our ability to directly contrast outcomes between surgical modalities within a controlled setting.

All surgical procedures in this series were performed by a single surgeon over two years (2020–2021), and cases were not stratified chronologically to assess potential learning curve effects. As the surgeon’s proficiency with the MITA technique likely evolved, early cases may have had different outcomes or complication rates compared to later cases. Prospective analyses that compare early, intermediate, and late cohorts would be valuable in determining whether surgeon experience influences the safety and efficacy of the procedure. Furthermore, because this study included only cases performed by a single surgeon at a single institution, the reproducibility of these findings in different clinical settings or among surgeons with varying levels of experience remains uncertain.

Another limitation of this study is the loss to follow-up among patients. Although most patients were initially scheduled for outpatient follow-up beyond one year, many discontinued visits due to symptom resolution and satisfaction with the surgical outcome. Consequently, the number of cases with a complete over one-year follow-up was smaller than the initial inclusion. To address this issue, the following studies should consider expanding the data collection period to include a broader patient population with longer follow-up availability. Our institution continues to perform MITA procedures and has now accumulated data on more than 4,000 feet. This growing dataset is being systematically organized and will serve as a valuable resource for addressing current limitations in future research.

Radiographic parameters—including hallux valgus angle, intermetatarsal angle, and sesamoid position—were measured by a single investigator without formal inter-rater reliability testing. This approach introduces the risk of measurement bias, as subtle variations in landmark identification or angle calculation may have influenced the reported degree of deformity correction. Incorporating blinded, independent reviewers or automated measurement tools in future studies would enhance the objectivity and reliability of radiographic assessments.

Unfortunately, the Manchester-Oxford Foot Questionnaire (MOXFQ) used in this study was administered using an unofficial Korean translation that has not been formally validated. Therefore, while the MOXFQ results are informative for within-study comparisons, their external generalizability may be limited. Validation of a standardized Korean MOXFQ instrument is essential to ensure the accuracy, reliability, and reproducibility of patient-reported outcomes in hallux valgus research.

Conclusion

This study demonstrates that MITA surgery is a feasible and effective approach for correcting hallux valgus, yielding improvements in radiographic parameters, functional outcomes, and pain relief. The postoperative complications were generally mild and transient, and cases of severe complications were also manageable. While these findings support MITA as a promising minimally invasive alternative to conventional procedures, they should be interpreted with caution given the certain limitations.

Notably, loss to follow-up occurred among some patients, resulting in a reduced number of cases with complete 1-year follow-up. To address this issue, the future studies should incorporate more extended data collection periods and include a larger number of cohorts. Our institution continues to perform MITA procedures and has accumulated data on over 4,000 feet, which will provide a more comprehensive basis for future research.

The inclusion of a larger number of cases in this study compared with previous reports enhances the statistical power. Nonetheless, further prospective, multicenter studies with extended follow-up are warranted to validate these outcomes and refine the technique.

Authors’ contributions

S.G.S. proposed the research topic, designed the study protocol, and oversaw all aspects of study execution as the attending physician and lead surgeon. J.H.L. contributed to study design, drafted the manuscript, prepared all figures and tables, explored key research questions, and provided critical orthopedic expertise. T.B.K. analyzed and organized clinical data, offered orthopedic insights, and participated in manuscript discussions. T.W.Y. analyzed and organized clinical data, offered orthopedic insights, and participated in manuscript discussions. D.L. analyzed and organized clinical data, offered orthopedic insights, and participated in manuscript discussions. All authors reviewed and approved the final manuscript.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study was approved by the Institutional Review Board of the Korea National Institute for Bioethics Policy (KoNIBP) (Approval No. P01-202506-01-028). As this was a retrospective study using anonymized data, the need for informed consent was waived.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.