Comparative efficacy of double and triple arthrodesis in adult-acquired flatfoot deformity: a retrospective analysis

Abstract

Background

Rigid adult-acquired flatfoot deformity (AAFD) often requires arthrodesis. While triple arthrodesis is standard, double arthrodesis has been proposed as an alternative. However, comparative evidence remains limited. This study compared their clinical efficacy, radiographic correction, and plantar pressure distribution.

Methods

Patients who underwent double or triple arthrodesis for rigid AAFD in our department from April 2013 to December 2019 were retrospectively reviewed. Outcomes included AOFAS scores, Foot Function Index (FFI), radiographic parameters (Meary’s angle [MA], talonavicular coverage angle [TCA], talus-first metatarsal angle [T1MA]), and plantar pressure measured via wireless insoles. Inter-group and intra-group comparisons were performed.

Results

Twenty-two patients were included (12 double, 10 triple arthrodesis). Baseline characteristics were comparable (all P > 0.05). Double arthrodesis had significantly shorter operative time (59.42 ± 6.05 vs. 85.80 ± 6.32 min, P < 0.001). Complication rates (16.67% vs. 10.00%, P = 1.0) and fusion time were similar, with 100% fusion in both groups. Both procedures significantly improved all functional and radiographic parameters (P < 0.05). AOFAS midfoot scores improved from 19.82 ± 6.97 to 73.83 ± 12.56 (double) and 23.80 ± 18.47 to 66.70 ± 16.65 (triple); hindfoot scores from 15.55 ± 11.57 to 68.75 ± 17.50 and 19.00 ± 17.83 to 69.60 ± 9.57; FFI decreased from 59.55 ± 13.77% to 22.58 ± 18.60% and 60.00 ± 16.26% to 33.50 ± 12.98%. Postoperative radiographic improvements included MA (23.53 ± 14.13° to 10.51 ± 6.90° double; 21.79 ± 9.24° to 10.32 ± 7.75° triple), TCA (13.20 ± 7.65° to 4.84 ± 4.72°; 9.80 ± 6.98° to 4.84 ± 4.88°), and T1MA (22.83 ± 12.00° to 11.49 ± 8.39°; 24.66 ± 9.41° to 10.26 ± 5.20°), with no significant inter-group differences. Plantar pressure showed postoperative symmetry between operated and healthy feet in both groups, with inter-group differences only in the lateral plantar region (P = 0.037) and entire sole (P = 0.048) before correction for multiple comparisons; neither remained significant after correction.

Conclusions

In this small cohort, no statistically significant differences were detected between the two procedures in short- to mid-term functional, radiographic, or plantar pressure outcomes, although operative time was shorter for double arthrodesis. Double arthrodesis may be considered a reasonable alternative in appropriately selected patients without significant CCJ involvement. However, these findings are exploratory and require confirmation in larger prospective studies.

Level of evidence

Level Ⅲ.

Introduction

Adult acquired flatfoot deformity (AAFD), now more accurately termed progressive collapsing foot deformity, is a progressive condition characterized by a progressive loss of the medial longitudinal arch, hindfoot valgus, and forefoot abduction [1–3]. This disease predominantly affects women and typically develops around the age of 55 years [3, 4]. The pathogenesis of AAFD is primarily associated with posterior tibial tendon dysfunction [5], although additional contributing factors such as ligamentous laxity and muscular insufficiency have been identified [6]. As the deformity progresses, patients frequently develop significant gait abnormalities, chronic pain, and functional limitations in daily activities, leading to severe loss of quality of life [7]. Initial treatment typically involves conservative measures, including custom orthotics, physical therapy programs, and nonsteroidal anti-inflammatory drugs [8]. However, for cases of advanced deformity where conservative treatment fails, particularly during the rigid or late stages of the disease when deformity has become fixed, surgical intervention is necessary. Surgical options vary based on the severity of the deformity, the joints involved, and the surgeons’ preference [9]. Common surgical procedures focus on medial arch reconstruction and symptom relief, incorporating techniques such as tendon transfers, corrective osteotomies, and hindfoot arthrodesis.

Historically, triple arthrodesis, which is defined as the fusion of the talonavicular, calcaneocuboid, and subtalar joints, has been the standard surgical procedure for addressing rigid AAFD [10–13]. This procedure achieves predictable deformity correction and provides long-term stability. However, in pursuit of preserving greater native foot mobility, minimizing surgical trauma, and potentially reducing postoperative complications (such as adjacent joint arthritis), double arthrodesis, which typically involves fusion of the talonavicular and subtalar joints while sparing the calcaneocuboid joint (CCJ), is increasingly becoming a viable alternative. Advocates argue that this approach can provide comparable deformity corrections while maintaining some hindfoot flexibility and offering more physiologically sound biomechanical properties [14–17].

Despite growing interest in double arthrodesis, the evidence base for direct comparisons between these two established techniques remains limited and often inconsistent. A comprehensive understanding of their relative efficacy in terms of patient-reported functional outcomes, the magnitude and sustainability of radiographic corrections, and their distinct impact on foot biomechanics, as reflected in plantar pressure distribution, is crucial for making informed surgical decisions. However, the absence of robust comparative data leaves surgeons without clear guidance on the potential trade-offs between these procedures. Therefore, this study was designed to conduct a retrospective comparative analysis of double versus triple arthrodesis for the management of rigid AAFD. Our primary objective is to perform a comprehensive assessment of the clinical efficacy of each procedure across three key domains: functional outcomes, radiographic parameters of deformity correction, and plantar pressure distribution patterns. Subsequently, we will conduct systematic inter-group comparisons between the two techniques in terms of these domains to explore comparative effectiveness. The findings from this investigation aim to provide substantive evidence to the existing literature, helping to clarify the comparative advantages and limitations of each technique, ultimately refining surgical strategies for this challenging condition.

Methods

The study has been approved by the institutional Human Subjects Review Board (Ethics approval number: EA4/150/21) and conducted in accordance with the Declaration of Helsinki. All participants signed informed consent form.

Data collection and patient selection

Following approval by the institutional ethics committee, a retrospective review was conducted on patients with AAFD who underwent either double or triple arthrodesis between April 2013 and December 2019 in our department. The following data were collected: demographic characteristics (age, gender, laterality, comorbidities, body mass index [BMI]), primary diagnosis, treatment details, functional foot scores, radiographic data obtained preoperatively, postoperatively, and during follow-up, total duration of follow-up, and plantar pressure distribution data at the final follow-up.

Inclusion criteria comprised patients with unilateral stage III AAFD that had failed prolonged conservative management and a contralateral asymptomatic foot. Staging was based on the Johnson–Strom classification [18] as modified by Myerson [19], in which stage III is defined as a fixed, rigid deformity with fixed hindfoot valgus and forefoot abduction that is not correctable to a neutral position on manual manipulation. Patients were excluded if they had a history of prior midfoot or hindfoot surgery, midfoot or hindfoot trauma, congenital foot deformities, or foot deformities secondary to rheumatoid or neurological diseases.

The choice between double and triple arthrodesis was made based on a combination of clinical factors rather than a single criterion. The primary determinant was the severity of CCJ degeneration, assessed preoperatively using the four-stage grading system proposed by Graves et al. [20] based on weight-bearing X-ray and computed tomography (CT): stage 0, arthritic change not appreciable; stage 1, narrowing of the joint space; stage 2, moderate subchondral sclerosis with osteophytes; and stage 3, severe sclerosis with significant narrowing and osteophyte formation. In general, patients with Graves grade 0–1 were considered candidates for double arthrodesis, while those with Graves grade 2–3 were considered for triple arthrodesis. However, the final surgical decision was not based solely on radiographic findings. Additional factors considered included patient-reported symptoms, patient preference, surgeon preference, and intraoperative findings. The distribution of CCJ degeneration for both groups is presented in Table 1.

Table 1.

Demographic characteristics and follow-up duration of patients undergoing double and triple arthrodesis

	Double arthrodesis (n = 12)	Triple arthrodesis (n = 10)	P-value
Age (years)	59.17 ± 11.57	60.10 ± 20.47	0.354
Gender			1.0
Male	4 (33.33%)	3 (30.00%)
Female	8 (66.67%)	7 (70.00%)
Laterality			0.666
Left	4 (33.33%)	5 (50.00%)
Right	8 (66.67%)	5 (50.00%)
Body Mass Index	28.62 ± 7.93	31.71 ± 9.44	0.222
Comorbidities
Osteoporosis	4 (33.33%)	3 (30.00%)	1.0
Hypertension	4 (33.33%)	4 (40.00%)	1.0
Diabetes	2 (16.67%)	2 (20.00%)	1.0
Smoking	7 (58.33%)	5 (50.00%)	1.0
CCJ degeneration			-
Stage 0	1 (8.33%)	0 (0%)
Stage 1	7 (58.33%)	1 (10.00%)
Stage 2	3 (25.00%)	3 (30.00%)
Stage 3	1 (8.33%)	6 (60.00%)
Follow-up (months)	36.50 ± 21.27	48.30 ± 23.41	0.230

*: CCJ, calcaneocuboid joint. CCJ status was assessed on the basis of the four-stage score proposed by Graves et al. [20]: stage 0, arthritic change not appreciable; stage 1, narrowing of the joint space; stage 2, moderate subchondral sclerosis with osteophytes; and stage 3, severe sclerosis with significant narrowing and osteophyte formation. Data are presented descriptively; no statistical comparison was performed, as CCJ degeneration was a primary determinant of surgical allocation

Surgical procedures

All patients underwent hindfoot arthrodesis under general or spinal anesthesia, administered according to standardized institutional protocols. Following meticulous skin preparation and sterile draping in the supine position, a pneumatic tourniquet was applied to the operative limb. The surgical approach was adapted to the planned procedure. For triple arthrodesis, a combination of a curved lateral incision along the peroneal tendons (extended distally toward the CCJ when necessary) and a separate medial incision over the talonavicular joint was used. For double arthrodesis, a lateral inframalleolar incision targeting the subtalar joint, combined with a medial approach to the talonavicular joint, was employed. Care was taken to protect neurovascular structures, notably the lateral dorsal cutaneous nerve (the continuation of the sural nerve). Arthrotomy was performed under direct visualization. The articular cartilage of the involved joints was denuded completely using osteotomes and curettes, and the subchondral bone was prepared by perforation or microfracture to promote vascular ingrowth. Autologous or allogeneic cancellous bone graft was placed into the prepared joint spaces prior to fixation in all cases. Reduction was performed sequentially, beginning with the subtalar joint to establish a neutral hindfoot axis, followed by correction of the forefoot. Temporary fixation with Kirschner wires was made to maintain the reduced position under fluoroscopic guidance. Definitive internal fixation was achieved using cannulated screws across the subtalar and talonavicular joints for both procedures. In triple arthrodesis, the CCJ was additionally stabilized, typically with screws or a small plate. For cases requiring enhanced stability, supplementary fixation with a dorsal plate across the talonavicular joint was employed optionally. Intraoperative fluoroscopy was used in multiple planes to confirm satisfactory joint apposition, hindfoot alignment, and hardware placement. The tourniquet was released for complete hemostasis prior to layer-by-layer wound closure. Additional procedures, when performed, were carried out during the same operative session. Details are presented in Table 2.

Table 2.

Comparison of perioperative and postoperative outcomes between double and triple arthrodesis

	Double arthrodesis (n = 12)	Triple arthrodesis (n = 10)	P-value
Operation time (minutes)	59.42 ± 6.05	85.80 ± 6.32	< 0.001*
Associated Surgery
Achilles lengthening	5 (41.67%)	5 (50.00%)	1.0
Peroneus tenotomy	3 (25.00%)	2 (20.00%)	1.0
Bone grafting			0.646
Autologous	8 (66.67%)	8 (80.00%)
Allogeneic	4 (33.33%)	2 (20.00%)
Talonavicular plate	2 (16.67%)	1 (10.00%)	1.0
Fusion rate
Overall	12 (100%)	10 (100%)	1.0
Subtalar	12 (100%)	10 (100%)	1.0
Talonavicular	12 (100%)	10 (100%)	1.0
Calcaneocuboid	-	10 (100%)	-
Fusion time (months)	4.67 ± 0.65	4.95 ± 0.80	0.370
Complications	2 (16.67%)	1 (10.00%)	1.0

*: Statistical significance at P < 0.05

Rehabilitation

A standardized rehabilitation protocol was followed. All patients received thromboembolism prophylaxis and standardized analgesia. Sutures were removed around 2 weeks post-surgery. The operated limb was immobilized in a Vacoped^® walking boot (OPED GmbH, Valley / Oberlaindern, Germany) with partial weight-bearing restricted to 15 kg for 6–8 weeks. Weight-bearing was then gradually increased, with full weight-bearing typically permitted 10–12 weeks postoperatively, depending on radiographic evidence of bony union. Progressive rehabilitation was initiated upon transition to full weight-bearing.

Clinical evaluation

Clinical outcomes were assessed through a retrospective analysis of patient-reported and functional measures obtained preoperatively and at the final follow-up. The American Orthopaedic Foot and Ankle Society (AOFAS) midfoot and hindfoot scoring systems were utilized to evaluate pain, function, hindfoot and midfoot motion, and alignment, with a maximum score of 100 points indicating optimal outcome [21]. The two scores were analyzed as separate outcome measures without combining overlapping items. Additionally, the Foot Function Index (FFI) was also employed, which comprises 23 items across three subscales, including pain, disability, and activity limitation, based on patient self-report [22, 23]. Patients rated each item on a scale from 0 (no pain / difficulty) to 10 (most severe pain / difficulty requiring assistance) to reflect their foot condition over the preceding week. The total FFI score was expressed as a percentage (total score divided by 230), where a higher percentage indicates poorer functional status.

Radiographic evaluation

Anteroposterior and lateral weight-bearing radiographs were routinely acquired during clinical follow-up visits until both radiographic and clinical union were confirmed. Radiographic union was defined as the presence of bridging trabeculae across more than half of the joint space without a discernible radiolucent line on two orthogonal views, in conjunction with complete resolution of pain under weight-bearing. Nonunion was determined at six months postoperatively through combined evaluation of clinical symptoms, plain radiographs, and CT. Notably, CT was not performed routinely during the first six months postoperatively. Instead, it was used selectively in cases where plain radiographs suggested fusion. At the six-month postoperative time point, CT was performed for patients whose plain radiographs had not clearly demonstrated fusion, to definitively confirm or rule out nonunion. To minimize detection bias, the two independent orthopaedists who were not involved in the patients’ clinical care performed the fusion assessment and were blinded to the patients’ functional outcomes (AOFAS, FFI) and plantar pressure data.

Angular measurements included Meary’s angle (MA) on lateral views, as well as the talonavicular coverage angle (TCA) and talus-first metatarsal angle (T1MA) on anteroposterior views. Preoperative and postoperative values of these angles were documented for comparative analysis.

Plantar pressure distribution analysis

Gait analysis was conducted at the final follow-up using wireless pressure-sensing insoles (medilogic^® WLAN insole 10.6.4) that were placed inside the shoes according to the manufacturer’s guidelines. All patients wore standardized, neutral-cushioned hospital socks and were fitted with appropriate insoles based on their shoe size during testing to minimize variability related to footwear. The insoles were calibrated according to the manufacturer’s protocol using a dedicated calibration station prior to each measurement session. Patients walked along a 10-meter level walkway at their self-selected comfortable walking speed, which was recorded for each trial using a stopwatch. Before formal data collection, each patient was instructed to walk along the walkway twice to familiarize themselves with the insole sensors and the experimental setup. A minimum of five valid gait cycles were recorded for each foot. Invalid steps, which were defined as those with visible gait initiation or termination, turning, or hesitation, were excluded from the analysis.

The plantar footprint was enclosed within a rectangular bounding box aligned with the long axis of the foot. Two horizontal lines were drawn to divide the box into three equal longitudinal sections, corresponding to the forefoot, midfoot, and hindfoot; a vertical midline was used to separate the medial and lateral columns. This approach yielded five plantar regions of interest for analysis: forefoot, midfoot, hindfoot, medial sole, and lateral sole (Fig. 1). Additionally, the entire sole, representing the whole footprint, was also included in the analysis as a separate region.

Fig. 1.

Schematic diagram of plantar regions.The sole is divided into five regions of interest for plantar pressure distribution analysis: forefoot, midfoot, hindfoot, medial sole, and lateral sole

While previous studies often relied on peak pressure or force-time integrals [24–26], the present analysis employed pressure-time integrals (PTIs) to assess postoperative plantar loading. PTIs offer a distinct advantage by quantifying cumulative pressure exposure over time within specific foot regions, thus providing a holistic view of load distribution throughout the gait cycle [27]. The assessor performing the data extraction and analysis was blinded to the surgical procedure.

The unaffected contralateral foot served as an internal control rather than referencing normative population data. This approach, supported by Kyung et al. [28] and Kizkapan et al. [29], helps control for individual variations in gait mechanics, weight distribution, and anatomy, thereby reducing inter-subject variability and enabling a more patient-specific evaluation of surgical outcomes on plantar pressure patterns.

Statistical analysis

SPSS Statistics version 27.0 for Windows (IBM Corp., Armonk, NY, USA) was employed for data analyses. Continuous variables were presented as mean ± standard deviation, while categorical data were expressed as frequency and percentage. Normality of data distribution was assessed using the Shapiro–Wilk test, and homogeneity of variances was evaluated with Levene’s test. For comparisons between the double and triple arthrodesis groups, independent samples t-test or Mann–Whitney U test was applied for continuous variables, and chi-square test or Fisher’s exact test was used for categorical variables. Within-group comparisons of preoperative and postoperative values were analyzed using paired samples t-test or Wilcoxon signed-rank test. This included functional scores, radiographic parameters, and PTIs. Notably, between-group comparisons of PTI values (for healthy and operated feet separately) and PTI inter-limb differences (ΔPTI) were performed using independent samples t-test or Mann–Whitney U test, as appropriate. To account for multiple comparisons, the Benjamini-Hochberg false discovery rate (FDR) method was applied separately within each domain for the between-group comparisons of change scores. The following families of tests were defined: functional score improvements (3 comparisons), radiographic angle corrections (3 comparisons), and inter-limb PTI differences (6 comparisons). Adjusted P values were calculated for each family, and an FDR threshold of q = 0.05 was used to determine statistical significance after correction. A p-value of less than 0.05 was considered statistically significant.

Results

Study population

A total of 51 patients with stage III AAFD who underwent either double or triple arthrodesis were initially identified. Of these, 10 patients were excluded due to loss to follow-up visit or incomplete postoperative imaging data, leaving 41 patients assessed for eligibility. After applying the exclusion criteria, 19 patients were further excluded: 9 due to bilateral involvement, 5 due to foot trauma or surgery history, 2 due to contralateral foot dysfunction, 1 due to congenital foot deformity, and 2 due to rheumatoid disease. The remaining 22 patients were included in the final analysis. Among them, 12 patients underwent double arthrodesis (4 males and 8 females), and the other 10 patients underwent triple arthrodesis (3 males and 7 females). A detailed patient flow diagram is presented in Fig. 2. The mean age of double and triple groups was 59.17 ± 11.57 and 60.10 ± 20.47 years, respectively, and the mean follow-up duration was 36.50 ± 21.27 (range, 11 to 90) and 48.30 ± 23.41 (range, 12 to 89) months, respectively. There were no statistically significant differences between the two groups in terms of age, gender, laterality, BMI, comorbidities, or duration of follow-up (all P > 0.05), confirming their comparability. Of note, the distribution of CCJ degeneration (Graves grades 0–3) was notably different between the two groups: in the double arthrodesis group, Graves grade distribution was 1, 7, 3, and 1 for grades 0, 1, 2, and 3, respectively; in the triple arthrodesis group, the distribution was 0, 1, 3, and 6. Detailed results are presented in Table 1.

Fig. 2.

Patient flow diagram

To assess whether the variable follow-up duration influenced the outcome comparisons, Spearman correlation analyses were performed between follow-up time and all primary outcome measures at final follow-up. No significant correlations were observed between follow-up duration and AOFAS midfoot score (r = -0.125, P = 0.579), AOFAS hindfoot score (r = -0.135, P = 0.549), FFI (r = 0.225, P = 0.314), MA (r = 0.010, P = 0.964), TCA (r = -0.252, P = 0.257), or T1MA (r = -0.320, P = 0.147). These findings suggest that the between-group outcome comparisons were not substantially confounded by differences in follow-up duration.

Perioperative and postoperative outcomes

The mean operative time was significantly longer in the triple arthrodesis group compared to the double arthrodesis group (85.80 ± 6.32 min vs. 59.42 ± 6.05 min, P < 0.001). Regarding postoperative complications, two patients in the double arthrodesis group experienced superficial infections at the medial incision, which were treated successfully with antibiotics and local wound care without the need for debridement. In the triple arthrodesis group, one patient presented with dehiscence of the lateral incision, which resolved following an extended course of antibiotics and local wound care. There was no statistically significant difference in complication rates between the two groups (16.67% vs. 10.00%, P = 1.0). No cases of delayed union or nonunion were observed in either group at the final follow-up. Joint-specific fusion rates were as follows: in the double arthrodesis group, the subtalar joint achieved fusion in all 12 patients (100%), and the talonavicular joint in all 12 patients (100%). In the triple arthrodesis group, the subtalar joint fused in all 10 patients (100%), the talonavicular joint in all 10 patients (100%), and the CCJ in all 10 patients (100%). Overall, all fused joints achieved bony union, yielding a global fusion rate of 100% in both groups. Moreover, the mean time to fusion was 4.67 ± 0.65 months in the double arthrodesis group and 4.95 ± 0.80 months in the triple arthrodesis group, with no statistically significant difference being reached between the two groups (P = 0.370). Details of perioperative outcomes, including additional procedures (Achilles lengthening and Peroneus tenotomy), bone graft type (autologous or allogeneic), and supplementary fixation for talonavicular joint, are summarized in Table 2.

Functional and radiographic results

Compared to preoperative data, both groups showed significant postoperative improvements in functional and radiographic outcomes. Specifically, in double arthrodesis group, AOFAS midfoot scores increased from 19.82 ± 6.97 to 73.83 ± 12.56 (mean difference [MD] = 54.02 ± 12.84, P < 0.001); AOFAS hindfoot scores from 15.55 ± 11.57 to 68.75 ± 17.50 (MD = 53.20 ± 14.20, P < 0.001); FFI decreased from (59.55 ± 13.77)% to (22.58 ± 18.60)% (MD = [36.96 ± 11.37]%, P < 0.001); MA reduced from 23.53 ± 14.13° to 10.51 ± 6.90° (MD = 13.02 ± 11.58°, P = 0.003); TCA from 13.20 ± 7.65° to 4.84 ± 4.72° (MD = 8.37 ± 9.25°, P = 0.010); T1MA from 22.83 ± 12.00° to 11.49 ± 8.39° (MD = 11.34 ± 10.46°, P = 0.003). Similarly, for triple arthrodesis group, AOFAS midfoot scores improved from 23.80 ± 18.47 to 66.70 ± 16.65 (MD = 42.90 ± 26.31, P < 0.001); AOFAS hindfoot scores from 19.00 ± 17.83 to 69.60 ± 9.57 (MD = 50.60 ± 23.79, P < 0.001); FFI decreased from (60.00 ± 16.26)% to (33.50 ± 12.98)% (MD = [26.50 ± 25.62]%, P = 0.010); MA from 21.79 ± 9.24° to 10.32 ± 7.75° (MD = 11.48 ± 10.97°, P = 0.009); TCA from 9.80 ± 6.98° to 4.84 ± 4.88° (MD = 4.95 ± 6.11°, P = 0.030); T1MA from 24.66 ± 9.41° to 10.26 ± 5.20° (MD = 14.40 ± 10.06°, P = 0.001). Representative preoperative and postoperative weight-bearing radiographs for patients undergoing double and triple arthrodesis are presented in Figs. 3 and 4, respectively.

Fig. 3.

Representative weight-bearing radiographs of a patient who underwent double arthrodesis. A Preoperative anteroposterior view. B Preoperative lateral view. C Postoperative anteroposterior view at final follow-up. D Postoperative lateral view at final follow-up

Fig. 4.

Representative weight-bearing radiographs of a patient who underwent triple arthrodesis. A Preoperative anteroposterior view. B Preoperative lateral view. C Postoperative anteroposterior view at final follow-up. D Postoperative lateral view at final follow-up

However, no statistically significant differences were observed between the two groups either in preoperative or postoperative values for any of these parameters (all P > 0.05; Table 3). Likewise, the postoperative functional improvement and radiographic corrections, regarding all parameters mentioned above, did not differ significantly between the two cohorts (all P > 0.05; Table 5).

Table 3.

Preoperative and postoperative functional and radiographic outcomes of double and triple arthrodesis

	Double arthrodesis (n = 12)	Triple arthrodesis (n = 10)	P-valuea
AOFAS Midfoot Score
Preoperative	19.82 ± 6.97	23.80 ± 18.47	0.532
Postoperative	73.83 ± 12.56	66.70 ± 16.65	0.266
P-valueb	< 0.001*	< 0.001*
AOFAS Hindfoot Score
Preoperative	15.55 ± 11.57	19.00 ± 17.83	0.590
Postoperative	68.75 ± 17.50	69.60 ± 9.57	0.892
P-valueb	< 0.001*	< 0.001*
FFI
Preoperative	(59.55 ± 13.77) %	(60.00 ± 16.26) %	0.944
Postoperative	(22.58 ± 18.60) %	(33.50 ± 12.98) %	0.105#
P-valueb	< 0.001*	0.010*
MA (°)
Preoperative	23.53 ± 14.13	21.79 ± 9.24	0.742
Postoperative	10.51 ± 6.90	10.32 ± 7.75	0.950
P-valueb	0.003*	0.009*
TCA (°)
Preoperative	13.20 ± 7.65	9.80 ± 6.98	0.292
Postoperative	4.84 ± 4.72	4.84 ± 4.88	0.895#
P-valueb	0.010*	0.030*
T1MA (°)
Preoperative	22.83 ± 12.00	24.66 ± 9.41	0.700
Postoperative	11.49 ± 8.39	10.26 ± 5.20	0.689
P-valueb	0.003*	0.001*

Data are presented as mean ± standard deviation

AOFAS American Orthopaedic Foot and Ankle Society, FFI Foot Function Index, MA Meary’s Angle, TCA Talonavicular Coverage Angle, T1MA Talus-first Metatarsal Angle

^a: Double vs. Triple arthrodesis

^b: Preoperative vs. Postoperative

 *: Statistical significance at P < 0.05

^#: Non-parametric tests were used instead of t-tests

Table 5.

Comparison of metric changes between double and triple arthrodesis

	Double (n = 12)	Triple (n = 10)	Mean Difference (95% CI)	Cohen’s d	Raw P-value	Adjusted P-value
Δ AOFAS Midfoot	54.02 ± 12.84	42.90 ± 26.31	11.12 [-6.80, 29.03]	0.554	0.210	0.630
Δ AOFAS Hindfoot	53.20 ± 14.20	50.60 ± 23.79	2.60 [-14.47, 19.68]	0.136	0.754	0.754
Δ FFI	(36.96 ± 11.37) %	(26.50 ± 25.62) %	10.46% [-6.64%, 27.56%]	0.546	0.255	0.383
Δ MA (°)	13.02 ± 11.58	11.48 ± 10.97	1.54 [-8.56, 11.65]	0.137	0.753	0.753
Δ TCA (°)	8.37 ± 9.25	4.95 ± 6.11	3.41 [-3.72, 10.55]	0.427	0.330	0.990
Δ T1MA (°)	11.34 ± 10.46	14.40 ± 10.06	-3.07 [-12.25, 6.12]	0.298	0.494	0.741
Δ Forefoot (N·s/cm²)	0.63 ± 1.85	0.90 ± 1.47	-0.27 [-1.77, 1.24]	0.157	0.718	0.862
Δ Midfoot (N·s/cm²)	0.03 ± 1.30	-0.63 ± 1.66	0.66 [-0.65, 1.98]	0.451	0.304	0.456
Δ Hindfoot (N·s/cm²)	0.34 ± 2.02	-1.10 ± 2.35	1.44 [-0.50, 3.38]	0.662	0.138	0.276
Δ Lateral sole (N·s/cm²)	0.56 ± 1.04	-0.60 ± 1.40	1.16 [0.08, 2.24]	0.958	0.037	0.222
Δ Medial sole (N·s/cm²)	0.32 ± 1.32	0.45 ± 1.42	-0.13 [-1.34, 1.09]	0.093	0.831	0.831
Δ Entire sole (N·s/cm²)	0.44 ± 0.82	-0.09 ± 0.62	0.53 [-0.11, 1.17]*	0.718	0.048#	0.144

Δ was presented as mean ± standard deviation; Δ = Postoperative – Preoperative (for AOFAS midfoot and hindfoot score); Δ = Preoperative – Postoperative (for FFI, MA, TCA, T1MA); Δ = Unaffected side – Operated side (for plantar pressure). Mean Difference = Double – Triple

AOFAS American Orthopaedic Foot and Ankle Society, FFI Foot Function Index, MA Meary’s Angle, TCA Talonavicular Coverage Angle, T1MA Talus-first Metatarsal Angle

* Mean Difference (95% CI) for Δ Entire sole was based on parametric estimation

^# Raw P-value for Δ Entire sole was derived from the Mann–Whitney U test. Adjusted P-values were calculated using the Benjamini-Hochberg false discovery rate (FDR) method, applied separately within each domain: functional scores (m = 3), radiographic parameters (m = 3), and plantar pressure regions (m = 6). An FDR threshold of q = 0.05 was used

Plantar pressure distributions

Regarding PTIs at the final follow-up, in the double arthrodesis group, the PTI values on the healthy side for the entire sole and for each of the five specific plantar regions were higher than those on the affected side. In the triple arthrodesis group, except for the midfoot and medial sole regions, all other PTI values were higher on the affected side than on the healthy side. However, no significant differences in terms of PTIs for entire sole as well as the five regions were observed between the affected and healthy sides within either group (all P > 0.05; Table 4). Furthermore, no significant differences were observed between the double and triple arthrodesis groups when comparing either the healthy sides or the affected sides for entire sole PTI or regional PTIs (all P > 0.05; Table 4).

Table 4.

Plantar pressure distribution in the unaffected and operated feet following double and triple arthrodesis

	Double arthrodesis (n = 12)	Triple arthrodesis (n = 10)	P-valuea
Forefoot
Unaffected foot	4.81 ± 1.58	4.91 ± 1.61	0.717#
Operated foot	4.18 ± 1.98	4.02 ± 1.62	0.839
P-valueb	0.263	0.087
Midfoot
Unaffected foot	3.54 ± 1.91	4.31 ± 2.89	0.467
Operated foot	3.51 ± 2.06	4.94 ± 3.42	0.262#
P-valueb	0.931	0.259
Hindfoot
Unaffected foot	6.47 ± 2.53	6.16 ± 2.39	0.772
Operated foot	6.13 ± 2.54	7.26 ± 2.71	0.326
P-valueb	0.572	0.172
Lateral sole
Unaffected foot	5.65 ± 2.2	5.58 ± 2.30	0.741#
Operated foot	5.09 ± 1.78	6.18 ± 2.21	0.262#
P-valueb	0.089	0.206
Medial sole
Unaffected foot	4.34 ± 1.40	4.72 ± 1.59	0.553
Operated foot	4.02 ± 1.72	4.28 ± 2.36	0.769
P-valueb	0.416	0.092#
Entire sole
Unaffected foot	5.00 ± 1.65	5.13 ± 1.76	0.863
Operated foot	4.56 ± 1.60	5.22 ± 2.07	0.411
P-valueb	0.090	0.663

Unit: N·s/cm²

^a: Double vs. Triple arthrodesis

^b: Unaffected vs. Operated foot

^#: Non-parametric tests were used instead of t-tests

Moreover, when the difference in PTI (healthy side minus affected side) for each plantar region was calculated and compared between the two groups, nominally significant differences were observed for the lateral sole (mean difference: 1.16 N·s/cm², 95% CI: 0.08 to 2.24, Cohen’s d = 0.958) and entire sole (mean difference: 0.53 N·s/cm², 95% CI: -0.11 to 1.17, Cohen’s d = 0.718) before correction for multiple comparisons (P = 0.037 and P = 0.048, respectively; Table 5; Fig. 5). However, after applying the Benjamini-Hochberg FDR correction for multiple comparisons, neither of these differences remained statistically significant (adjusted P > 0.05). No significant differences were observed for the remaining plantar regions, despite some numerical variations (all P > 0.05; Table 5; Fig. 5).

Fig. 5.

Comparison of regional pressure-time integrals between the operated foot and non-operated foot under double arthrodesis and triple arthrodesis surgical approaches, respectively

Discussion

Studies comparing the clinical outcomes of double versus triple arthrodesis are relatively scarce [14, 30–35], and few have incorporated postoperative plantar stress analysis in addition to functional and radiographic evaluations, as conducted in this study. Our findings indicate that both double and triple arthrodesis can effectively improve functional scores and radiographic parameters in AAFD patients, suggesting reduced pain, enhanced function, and satisfactory correction of deformity postoperatively. Furthermore, plantar pressure distribution showed no significant difference between the affected and healthy sides after surgery, suggesting that no detectable asymmetry was present at final follow-up (Table 4; Fig. 2). However, no significant differences were observed between the two groups in terms of functional, radiographic, or pedobarographic outcomes (Tables 3 and 4). Notably, the operative time for double arthrodesis was significantly shorter than that for triple arthrodesis (Table 2).

Fusion rate is closely related to surgical technique and serves as a direct and important indicator for evaluating the efficacy of surgical interventions. In our study, all patients achieved complete fusion within 4–5 months postoperatively, regardless of whether they underwent double or triple arthrodesis (Table 2). Our findings are consistent with the conclusions reported by Fadle et al. [14]. However, previous literature has also reported inconsistent results. In the study by Walsh et al. [31], both the double and triple arthrodesis groups achieved a 100% fusion rate in the subtalar joint, but the fusion rate for the talonavicular joint was 87.3% in the double arthrodesis group and 82.1% in the triple arthrodesis group. Additionally, the double arthrodesis group showed a 7.1% nonunion rate in the CCJ. In the study by Burrus et al. [34], the double arthrodesis group had a 100% fusion rate in the subtalar joint, but a 44% nonunion rate and a 33% incomplete fusion rate in the talonavicular joint, whereas the triple arthrodesis group achieved a 100% fusion rate. In the case series by Jagodzinski et al. [35], which employed arthroscopic techniques for hindfoot arthrodesis, all four patients who underwent triple arthrodesis achieved complete fusion, whereas three out of fourteen patients who received double arthrodesis experienced nonunion of the subtalar joint. The differences between these studies and ours may be attributed to heterogeneity in patient populations, variations in surgical techniques, and differences in surgeon experience. Nevertheless, we must acknowledge that our relatively small sample size could have led to an overestimation of the fusion rate.

Notably, compared with the double arthrodesis group, the triple arthrodesis required a significantly longer average operative time and showed a tendency toward a longer period to achieve complete fusion, although the latter difference did not reach statistical significance (Table 2). These findings are consistent with the results reported by Walsh et al. [31] and Jagodzinski et al. [35], respectively. This is likely due to the additional CCJ procedure in triple arthrodesis, which not only extends the surgery duration but also results in extra surgical trauma that potentially prolongs the postoperative recovery period. Moreover, from a theoretical perspective, achieving bony fusion across three joints may naturally take longer time than across two joints in patients with comparable baseline characteristics.

Regarding postoperative complications, only incision-related adverse events were observed in both groups. Due to long-term valgus deformity, the lateral soft tissues of the foot often develop contracture. After correcting the valgus deformity, these lateral tissues are placed under tension. This condition is further exacerbated by the extended lateral incision used in triple arthrodesis, making the lateral wound more susceptible to soft tissue necrosis and subsequent infection. In contrast, double arthrodesis employs a much shorter lateral incision in an area with relatively relaxed soft tissues, which is generally considered safer, though it may still suffer from incision-related complications due to factors such as improper or excessive intraoperative tissue retraction, vascular compromise due to local dissection, and use of electrocautery. In our study, two cases of superficial infection at the medial incision occurred in the double arthrodesis group, and one case of lateral wound dehiscence was observed in the triple arthrodesis group. Nevertheless, no statistically significant difference was found between the two groups (16.67% vs. 10.00%, P = 1.0), and fortunately, all complications resolved with conservative treatment. In the study by Fadle et al. [14], one incision-related complication was reported in each group (13 double arthrodesis vs. 10 triple arthrodesis patients), with no significant difference between the surgical groups, consistent with our findings. Furthermore, the arthroscopic case series by Jagodzinski et al. [35] reported no perioperative complications. Interestingly, larger studies by Walsh et al. [31] (86 double arthrodesis vs. 28 triple arthrodesis patients) and Gauthier et al. [30] also found no statistically significant difference in postoperative complication rates between the double and triple arthrodesis groups (2/67 vs. 5/118, P > 0.05). This suggests that, with advancements in surgical techniques and implant materials, both double and triple arthrodesis have developed into established and safe surgical procedures.

Our study compared preoperative functional scores and radiographic angular measurements of deformity between patients undergoing double arthrodesis and those undergoing triple arthrodesis. The results showed no significant differences in preoperative functional status or severity of deformity, indicating good baseline comparability between the two groups. Postoperatively, both groups achieved satisfactory functional scores that represented statistically significant improvement from preoperative levels. Between the two groups, however, only numerical but not statistically significant differences were observed (Table 3). This finding aligns with the results reported by Fadle et al. [14], although their study used only the AOFAS hindfoot score as the sole functional assessment tool. Furthermore, considering potential differences in preoperative baseline values, we also compared the pre-to-postoperative score changes between the two groups. Again, no statistically significant difference in functional improvement was detected between the two groups in this limited cohort (Table 5). Notably, the mean improvements in all three functional parameters were numerically greater in the double arthrodesis group than in the triple arthrodesis group, although these differences did not reach statistical significance. However, in the study by Burrus et al. [34], patients who underwent double arthrodesis demonstrated significantly lower postoperative scores in the Foot and Ankle Ability Measure (FAAM) Activities of Daily Living (ADL) subscale, the Foot and Ankle Outcome Score (FAOS) ADL subscale, and the FAOS Quality of Life subscale compared to those in the triple arthrodesis group. Nevertheless, their study did not assess whether there were significant preoperative differences in these metrics between the two groups, making it unclear whether patients receiving double arthrodesis already had significantly lower baseline scores. Additionally, they did not compare the magnitude of increases from preoperative to postoperative scores between the two surgical approaches, leaving the difference in functional improvement unexplored.

To determine whether the observed within-group improvements are clinically meaningful, we interpreted our findings against the minimal clinically important difference (MCID) thresholds reported in the literature. Although disease-specific MCIDs for the AOFAS midfoot or hindfoot score and the FFI have not been established specifically for hindfoot arthrodesis, published values for foot and ankle surgery provide useful references. For the AOFAS scale, MCID values have been reported to range from approximately 8 to 12 points in foot and ankle populations [36–38]. The observed improvements in our study in both double (54.0 points) and triple arthrodesis group (42.9 points) substantially exceed this range. Similarly, for the FFI, a total score improvement of approximately 19 points has been reported as the MCID for foot and ankle surgery [39], whereas our study demonstrated improvements of 36.96% points (double) and 26.50% points (triple), far exceeding this threshold. These findings confirm that the statistically significant improvements achieved by both procedures are also clinically meaningful from the patients’ perspective.

Similarly, in the present study, all three radiographic angles improved significantly postoperatively in each group compared to preoperative values (Table 3). No statistically significant differences were detected between the two groups in any of the three radiographic angles, whether assessed as preoperative values, postoperative values, or the degree of deformity correction (Table 3). Our findings are consistent in part with those of DeVries et al. [33], who reported similar outcomes using six radiographic parameters: anteroposterior and lateral talocalcaneal angle, T1MA, MA, calcaneal inclination angle, and talar declination angle. In their study, both procedures significantly improved all six parameters postoperatively, with no statistically significant differences between the two groups in postoperative values. However, unlike our study, they did not further calculate or compare the mean differences from preoperative to postoperative values for each parameter between the groups. In another study by Fadle et al. [14], in addition to the three angles used in our study, three other radiographic parameters were assessed: the Calcaneo-MT1 (Hibb’s) angle, calcaneal pitch angle, and cuneiform-MT5 height. Interestingly, their results showed that neither double nor triple arthrodesis significantly improved T1MA, while the other five radiographic parameters improved significantly postoperatively, with no statistically significant difference between the two procedures regarding pre-to-postoperative changes of any of the six radiographic parameters. Clearly, our findings differ from theirs regarding T1MA correction. The authors did not discuss this negative finding in detail, possibly because the significant improvements in the other five parameters were deemed sufficient to demonstrate the corrective effect of both procedures. We believe the discrepancy may result from differences in the baseline deformity severity between the two study populations. In their study, the preoperative T1MA ranged from 11° to 14°, with postoperative changes of only 0.30°–0.48°. In contrast, our patients had a substantially higher preoperative T1MA (22°–24°). Although postoperative values improved to approximately 10°–11°, which is close to the preoperative levels in their cohort, the greater preoperative abnormality in our series likely allowed more noticeable correction. On the other hand, since preoperative surgical planning prioritizes the correction of major deformities, a mild T1MA abnormality that was reported by Fadle et al. [14] may not be actively addressed, whereas an obvious deformity, as seen in our patients, would naturally be targeted during surgery.

As one of the methods for gait analysis, plantar stress distribution analysis has been widely used in clinical orthopaedic researches [40–44]. However, to our knowledge, no previous study has compared plantar pressure distributions after double versus triple arthrodesis prior to our investigation. Most researches involving pedobarographic analysis have focused on comparing preoperative and postoperative values in the affected limb [25, 45–48]. In contrast, much fewer studies have compared the differences between the affected and unaffected sides within the same individual [28, 29, 49]. In a recently published retrospective study in 2025 examining plantar pressure distribution after isolated talonavicular arthrodesis [50], the healthy foot was used as a control, as it was considered to help minimize inter-individual variability and allow for a more accurate and individualized assessment of surgical impact on plantar pressure distribution. By adopting a similar methodology, our present study showed no significant differences regarding PTIs between the affected and healthy sides within either surgical group at final follow-up, suggesting the absence of detectable postoperative asymmetry. Between-group comparisons similarly showed no significant differences in any region for either the healthy or operated side (Table 4).

However, it is noteworthy that in the double arthrodesis group, PTI values across the entire sole and in each specific plantar region were numerically higher on the healthy side than on the affected side, whereas in the triple arthrodesis group, this pattern was observed only in the midfoot and medial sole, with all other plantar regions showing higher values on the affected side. These numerical differences did not reach statistical significance (all P > 0.05). Moreover, when comparing the inter-limb differences (healthy minus affected sides) between the two surgical groups, nominally significant differences were observed for the entire sole and the lateral sole before correction for multiple comparisons (P = 0.048 and P = 0.037, respectively; Table 5). However, after applying the Benjamini-Hochberg FDR correction, neither remained statistically significant. Whether these exploratory observations suggest distinct patterns of load redistribution between the two procedures remains unclear and warrants further investigation in larger, prospective studies with comprehensive biomechanical and gait analyses.

Several limitations should be considered when interpreting the results of this study. First, the sample size was relatively small, which may limit the statistical power to detect subtle differences between the double and triple arthrodesis groups, particularly in secondary outcomes such as regional plantar pressure patterns or complication rates. Additionally, 10 patients were excluded from the initial cohort because of loss to follow-up or incomplete postoperative imaging. While all 22 included patients completed the final assessment, the excluded cases may have been more likely to represent poorer outcomes, which could introduce selection bias and limit the generalizability of our findings. Second, the non-randomized allocation of patients based on CCJ status and other clinical factors introduces potential selection bias. As shown in Table 1, the two groups had markedly different baseline CCJ degeneration, reflecting the clinical selection process: patients with more severe CCJ involvement received triple arthrodesis, while those with less severe CCJ involvement received double arthrodesis. Therefore, these groups should not be interpreted as interchangeable treatment arms; rather, this study compares outcomes in patients selected for each procedure according to clinical and radiographic features. This baseline imbalance limits direct procedural comparisons. Third, the follow-up period was variable and, while adequate for assessing fusion and early functional recovery, is insufficient to assess long-term outcomes such as adjacent joint degeneration, implant-related symptoms, or late functional decline. The wide follow-up range (11 to 90 months) and small sample size further limit our ability to evaluate the durability of the observed outcomes or the incidence of late complications. Fourth, the study was conducted at a single center, and surgical techniques, although standardized, were not performed by the same surgeon, which may introduce variability in operative execution and postoperative management. Fifth, fusion assessment was based primarily on plain weight-bearing radiographs throughout the follow-up period. CT was used selectively: before six months, to confirm fusion suggested by plain radiographs; and at six-month time point, to confirm nonunion in patients whose radiographs had not clearly demonstrated fusion. Therefore, CT was not performed uniformly for all patients, which may have led to underestimation of nonunion rates, particularly at the talonavicular joint where overlapping anatomy can obscure the fusion site. Sixth, pedobarographic assessment was performed only at final follow-up without preoperative data, so we cannot demonstrate changes in plantar pressure from baseline; we can only compare postoperative symmetry between the operated and contralateral feet. Furthermore, the contralateral asymptomatic foot, while serving as a practical internal control, may itself be affected by compensatory loading patterns or early asymptomatic deformity in patients with long-standing unilateral flatfoot. Seventh, pedobarographic assessment was performed under strictly controlled walking conditions and may not fully represent the dynamic and varied loading patterns during daily or high-demand activities. Finally, while we compared preoperative and postoperative radiographic angles, the analysis did not include all possible radiographic parameters such as Hibb’s angle or calcaneal pitch that are sometimes used in comprehensive deformity assessment, which may have provided additional insight into correction mechanics.

Despite these limitations, this study offers a direct comparative analysis of double versus triple arthrodesis in AAFD, incorporating functional, radiographic, and novel plantar pressure data. The findings highlight areas for further investigation in larger, prospective, and longer-term studies and may offer preliminary information to inform surgical decision-making in appropriately selected patients.

Conclusion

In this limited retrospective cohort on treatment of AAFD, no statistically significant differences were detected between double and triple arthrodesis in functional outcomes (AOFAS midfoot and hindfoot scores, FFI), radiographic parameters (MA, TCA, T1MA), or plantar pressure symmetry. Furthermore, no significant differences were observed in fusion rate, time to complete fusion, or postoperative complications. Nevertheless, double arthrodesis may be considered a reasonable alternative in appropriately selected patients without significant CCJ involvement, given its shorter operative time. However, these findings are exploratory. Larger prospective studies with adequate power are required before definitive conclusions can be drawn.

Abbreviations

AAFD

Adult acquired flatfoot deformity

BMI

Body mass index

CCJ

Calcaneocuboid joint

AOFAS

American Orthopaedic Foot and Ankle Society

FFI

Foot Function Index

MA

Meary’s angle

TCA

Talonavicular coverage angle

T1MA

Talus-first metatarsal angle

PTI

Pressure-time integral

FDR

False discovery rate

MD

Mean difference

FAAM

Foot and Ankle Ability Measure

ADL

Activities of Daily Living

FAOS

Foot and Ankle Outcome Score

MCID

Minimal clinically important difference

Authors’ contributions

Conceptualization: Chaoqun Wang, Khalil Alqiq, Tobias Gehlen. Project administration: Xugui Li, Zexi Ling, Serafeim Tsitsilonis, Tobias Gehlen. Resources: Chaoqun Wang, Shengnan Dong, Frank Graef, Khalil Alqiq, Tobias Gehlen. Supervision: Xugui Li, Zexi Ling, Serafeim Tsitsilonis, Tobias Gehlen. Visualization: Chaoqun Wang, Shengnan Dong, Frank Graef, Khalil Alqiq. Writing – original draft: Chaoqun Wang, Shengnan Dong, Zexi Ling, Khalil Alqiq. Writing – review & editing: Chaoqun Wang, Xugui Li, Shengnan Dong, Zexi Ling, Serafeim Tsitsilonis, Frank Graef, Khalil Alqiq, Tobias Gehlen.

Funding

No funding was received for conducting this study.

Data availability

All data in this study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the Ethics Committee of Charité—Universitätsmedizin Berlin (EA4/150/21) and conducted in compliance with the Declaration of Helsinki. Informed consent was obtained from all participants.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.