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When ankle joint diseases progress to the end stage, patients typically experience persistent weight-bearing pain, skeletal deformities, functional limitations, and loss of work capacity . At present, ankle arthrodesis remains a well-established, widely accepted intervention for end-stage ankle diseases—and has long been regarded as a clinical gold standard for this condition. It achieves therapeutic efficacy by effectively halting progressive joint lesions, correcting deformities, alleviating pain, stabilizing the tibiotalar joint, and restoring functional capacity ^,,, . Currently, it exists alongside total ankle replacement as a core treatment option for end-stage ankle diseases, with each approach offering distinct advantages tailored to different patient profiles.

Proper positioning of ankle arthrodesis is an important surgical principle . Residual malpositioning after ankle arthrodesis can lead to functional impairments . While mild deformities may be amenable to conservative management, severe cases often require secondary revision surgery ^, . Current literature predominantly focuses on nonunion complications ^, , arthroscopic methods ^, , and comparative outcomes with ankle replacement ^, . Limited research has specifically addressed malpositioning during ankle arthrodesis. Notably, clinical observations indicate that such flaws are not uncommon in clinical practice ^, .

Malpositioning in ankle arthrodesis is inherently a technical issue in surgical practice, occurring in the sagittal, coronal, or transverse plane, or as a combination of multiple planes. Given the subtalar joint’s compensatory effect on the tibiotalar joint in the coronal plane, analyzing post-arthrodesis hindfoot varus or valgus in this plane necessitates integration with concurrent management strategies for the subtalar joint. Furthermore, due to the paucity of weight-bearing computed tomography (CT) data, assessing rotational malalignment in the transverse plane using radiographs alone remains challenging. For these reasons, the present study focuses specifically on sagittal plane deformities. We conducted a retrospective analysis of patients with end stage ankle joint diseases who underwent primary arthrodesis, aiming to explore the specific risk factors for sagittal plane malpositioning. We hypothesized that the most frequent problem is the ineffective correction of preoperative deformities. The selection of surgical approaches and internal fixation systems may also have an impact, and the surgical experience of the operating surgeons is likely to be an influencing factor. Through our research, we hope to guide clinical practice in paying sufficient attention to patients with these high-risk factors and adopting reasonable treatment plans.

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This study was a retrospective cohort analysis involving primary ankle joint arthrodesis cases performed at our hospital. The study received ethical clearance from the ethics committee of our hospital, with all protocols strictly conforming to established ethical standards.

The following inclusion criteria were applied: (1) Patients who underwent primary ankle joint arthrodesis for end-stage ankle joint diseases at our institution between January 2010 and December 2019. (2) Primary ankle joint arthrodesis was defined as the first fusion of tibiotalar joints, regardless of the concomitant procedures of adjacent joints (e.g., subtalar joint). (3) Cases with complete clinical data and surgical details, including preoperative and postoperative radiological assessments and surgical records.

The following exclusion criteria were applied: (1) Patients with incomplete clinical or radiological data. (2) Cases involving revision ankle arthrodesis. (3) Patients in subgroups with insufficient sample sizes for statistical analysis (n ≤ 5) were excluded from the study.

There are two main types of sagittal plane malpositioning after ankle arthrodesis: translational ones and angular ones. Translational malpositioning refers to the shift of the talus relative to the tibial plafond. Angular malpositioning refers to the postoperative pes equinus or pes calcaneus deformities. These two subtypes often coexist in the same patient.

In this study, the following were considered sagittal plane malpositioning of primary ankle arthrodesis: talar translation > 5 mm, or sagittal plane angulation > 10° postoperatively.

Talar translation is defined as the displacement of the talus relative to the tibial axis in the sagittal plane. The tibial axis is the longitudinal axis of the tibia formed by connecting the midpoints of the shaft and distal diaphysis of the tibia. For the detailed measurement method, first, regarding the determination of reference points, the posterior talar point is defined as the most posterior end of the subtalar joint contact surface, which is the preferred reference point for measuring talar translation; if the posterior talar point cannot be clearly identified due to issues such as image clarity, the anterior talar point (the most dorsal point of the talonavicular joint) is used as an alternative reference point. Second, in terms of the measurement and calculation method, the vertical distance between the above-mentioned reference point (either the posterior or anterior talar point) and the tibial axis is measured, and the talar translation distance is obtained as the difference between the measured value on the affected side and that on the unaffected (normal) side ( Fig. 1 ).

Measurement of talar translation in the ankle joint. A, Lateral weight-bearing radiograph of the unaffected (normal) ankle joint. Line a represents the tibial axis, defined as the longitudinal line connecting the midpoints of the shaft and distal diaphysis of the tibia. Point b indicates the posterior talar point (the most posterior end of the subtalar joint contact surface), and the vertical distance from point b to line a reflects the position of the talus in the unaffected side. B, Postoperative lateral radiograph of the affected ankle joint. The measurement method is consistent with that in (A): line a denotes the tibial axis, and the vertical distance from the posterior talar point ( b ) to line a indicates the talar position in the affected side. Talar translation is calculated as the difference between the vertical distance measured in the affected side (B) and the unaffected side (A). A talar translation exceeding 5 mm is considered malposition.

The talar axis is a straight line drawn from the inferior edge of the posterior talar tubercle to the inferior edge of the talar neck, serving as the axis of the talus. The angle between the tibial axis and the talar axis is the sagittal tibio-talar angle. Sagittal angulation is defined as the difference between the sagittal tibio-talar angle of the affected side after fusion and that of the unaffected side in the neutral position ( Fig. 2 ).

Measurement of the sagittal tibio-talar angle in the ankle joint. A, Radiograph of the unaffected (normal) ankle joint in neutral position, showing the measurement of the sagittal tibio-talar angle. The tibial axis is defined as the longitudinal line connecting the midpoints of the shaft and distal diaphysis of the tibia; the talar axis is a straight line drawn from the inferior edge of the posterior talar tubercle to the inferior edge of the talar neck. The sagittal tibio-talar angle refers to the angle formed between these two axes. B, Postoperative radiograph of the affected ankle joint after arthrodesis, with the sagittal tibio-talar angle measured using the same method as in (A). Note that a screw in (B) is suspiciously positioned within the talonavicular joint, which is not within the scope of this study. Sagittal angulation is calculated as the difference between the sagittal tibio-talar angle of the affected side after fusion and that of the unaffected side in neutral position. A sagittal angulation exceeding 10° is considered malposition.

Patients with normal ankle alignment after primary arthrodesis but subsequent displacement due to other causes such as nonunion, bone resorption, or internal fixation failure; such cases were not classified as malpositioning in this study.

We analyzed age, gender, affected side, primary disease, preoperative anteroposterior (AP) alignment, preoperative lateral (LA) alignment, surgical approach, fixation system, concomitant procedures, and stratification of the primary surgeon as potential risk factors.

To facilitate statistical evaluation, we categorized the primary diseases into three groups. Osteoarthritis, Charcot’s disease, hemophilia arthritis, rheumatoid arthritis, gouty arthritis and infection patients with intra-articular inflammation and degeneration of joints were classified into the inflammatory arthritis group (abbreviated as the Arthritis Group). Those with a history of fractures or sprains as the initial factor were classified into the Injury Group. Those with structural abnormalities caused by congenital factors or chronic biomechanical imbalances were classified into the Deformity Group.

The alignment status of the tibiotalar joint was determined via standardized analysis of preoperative weight-bearing radiographs. Key parameters, including the tibial articular surface angle, tibial lateral surface angle, talar tilt angle, tibiotalar surface angle, talar translation, and sagittal angulation, were measured using PACS-integrated digital measurement tools ^, . The preoperative weight-bearing mechanical axis was evaluated on anteroposterior (AP) ankle radiographs to assess varus and non-varus deformities. Lateral ankle radiographs were analyzed to determine the presence of preoperative pes equinus/anterior talar subluxation or their absence. Two attending physicians (A and B) with extensive expertise in foot and ankle surgery, who were blinded to patients’ surgical approach, surgeon experience, and other intraoperative details, performed qualitative assessments on study materials based on pre-specified thresholds, including preoperative AP alignment, preoperative LA alignment, and postoperative malposition. In case of disagreement, a third chief physician (C) conducted an independent reassessment. Inter-rater agreement was analyzed using Cohen’s kappa: unweighted kappa for binary variables (2 ×2 contingency tables, asymptotic 95 % CIs, Landis & Koch criteria).

The surgical approaches were categorized as anterior, medial, lateral, posterior, and minimally invasive (including small-incision and arthroscopic ones). The fixation systems included dorsal plate plus cannulated screws, lateral plate plus cannulated screws, posterior plate plus cannulated screws, isolated cannulated screws, isolated plate, intramedullary nail. Given the close association between surgical approaches and fixation methods- for example, dorsal plate is typically utilized with anterior approach, posterior plate with posterior approach, and lateral plate with lateral approach- the two variables exhibit multicollinearity. Therefore, they were merged into a single variable, with the anterior part indicating the surgical approach and the posterior part denoting the fixation system, such as “anterior approach + dorsal plate plus cannulated screws”. This consolidation addresses the issue of multicollinearity while retaining the essential relationship between the surgical access and fixation device, ensuring the robustness of the analytical model.

In the present study, among the concomitant procedures—including subtalar arthrodesis, talonavicular joint fusion, calcaneal osteotomy, fibular osteotomy, soft tissue release (encompassing Achilles tendon lengthening), and foot correction- only the most prevalent one, subtalar arthrodesis, was subjected to statistical analysis, with the remaining concomitant procedures classified as “non-subtalar arthrodesis”.

The primary surgeon was stratified by experience level, with senior surgeons defined as those possessing over a decade of specialized experience in ankle surgery and having accumulated at least 100 ankle arthrodesis cases, while mid-senior surgeons were classified as practitioners with fewer than ten years of operative experience in this specialty and having accumulated at least 30 ankle arthrodesis cases. Given the long-time span of the study and the professional growth of physicians over time, the stratification of primary surgeons was assessed based on the specific time point when each patient’s surgery was performed. This classification aligns with the standardized local medical training pathway: After completing standardized residency training, physicians undergo a 3-year subspecialty fellowship. Following this, they engage in another 2–5 years of clinical practice to attain full surgical autonomy for ankle arthrodesis. This milestone authorizes them to lead surgical teams and assume corresponding responsibilities, with supervising surgeons overseeing pre-surgical evaluation and post-operative assessment. With an additional 5–10 years of clinical practice, practitioners may advance to senior career stages based on cumulative years of specialized experience. Data was sourced from the hospital’s surgical credentialing system, which systematically tracks case volume, procedure complexity, and years of dedicated ankle surgery practice.

Data analysis was performed using SPSS software (version 25.0). Binary logistic regression was employed to evaluate the association between postoperative deformities (dependent variable) and covariates, including age, gender, affected side, primary disease, preoperative anteroposterior (AP) alignment, preoperative lateral (LA) alignment, merge variable of surgical approach and fixation system, concomitant procedures, and stratification of the primary surgeon. The latter eight variables were treated as categorical covariates, with the first category serving as the reference group. Adjusted odds ratios (ORs) with 95 % confidence intervals (CIs) were calculated to quantify risk factors. A p -value < 0.05 was defined as statistically significant.

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Among the 189 enrolled patients, 13 with incomplete data were excluded. The breakdown of surgical approaches combined with fixation systems was as follows: 68 cases using anterior approach + dorsal plate plus cannulated screws, 64 cases using anterior approach + cannulated screws, 34 cases using lateral approach + lateral plate plus cannulated screws, 5 cases using anterior approach + plate, 3 cases using minimally invasive approach + intramedullary nail, and 2 cases using posterior approach + posterior plate plus cannulated screws. Subgroups with insufficient sample sizes for statistical analysis (n ≤ 5) were excluded from the study. After enrollment and application of exclusion criteria, a total of 166 cases remained.

The average age of these patients was 51.68 years, with 78 males (46.99 %) and 88 females (53.01 %), 86 cases (51.81 %) are left-sided and 80 (48.19 %) are right-sided. The primary diseases vary, with 74 cases of Arthritis Group (44.58 %), 38 cases of Injury Group (22.89 %), and 54 cases of Deformity Group (32.53 %).

Preoperative AP alignment shows 91 varus cases (54.82 %) and 75 cases in the non-varus category (45.18 %). For preoperative LA alignment, 100 cases are pes equinus and/or anterior subluxation of the talus (60.24 %) and 66 are in the non-subtalar arthrodesis category (39.76 %).

In terms of concomitant procedures, 58 cases (34.94 %) underwent subtalar arthrodesis, while 108 cases (65.06 %) did not. Additionally, 79 cases (47.59 %) were performed by senior doctors, and 87 cases (52.41 %) by mid-senior doctors. ( Table 1 ).

Table 1

Distribution of variables in 166 patients undergoing primary ankle arthrodesis.

Variables Table
Variables	Specific Variable	Classification/Definition	Counts (n)	Percentage (%)	Reference Group
Outcome Variable	Sagittal plane malpositioning	Postoperative talar translation > 5 mm or sagittal angulation > 10°	27	16.3	No sagittal malpositioning
		No sagittal malpositioning	139	83.7
Demographic Variables	Age	Continuous variable (mean age: 51.68 years)	/	/	/
	Gender	Male	78	46.99	Female
		Female	88	53.01
	Affected side	Left-side	86	51.81	Left-side
		Right-side	80	48.19
Clinical Variables	Primary disease	Arthritis Group (inflammatory/degenerative joint diseases)	74	44.58	Arthritis Group
		Injury Group (post-traumatic)	38	22.89
		Deformity Group (congenital/biomechanical abnormalities)	54	32.53
	Preoperative AP alignment	Varus	91	54.82	Non-varus
		Non-varus	75	45.18
	Preoperative LA alignment	Pes equinus and/or anterior talar subluxation	100	60.24	Absence of pes equinus and/or anterior talar subluxation
		Absence of above deformities	66	39.76
Surgical Variables	Surgical approach + fixation system	Anterior approach + dorsal plate plus cannulated screws	68	40.96	Anterior approach + cannulated screws alone
		Anterior approach + cannulated screws alone	64	38.55
		Lateral approach + lateral plate plus cannulated screws	34	20.48
	Concomitant procedures	Subtalar arthrodesis	58	34.94	Non-subtalar arthrodesis
		Non-subtalar arthrodesis	108	65.06
	Surgeon experience	Senior surgeons (≥10 years of specialized ankle surgery experience)	79	47.59	Senior surgeons
		Mid-senior surgeons (<10 years of specialized ankle surgery experience)	87	52.41

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