Accuracy of Patient-Specific Instruments for Supramalleolar Osteotomies

Abstract

Background:

Supramalleolar osteotomy (SMO) enables deformity correction of the distal tibia, but the procedure remains technically demanding. Patient-specific instruments (PSIs) have the potential to mitigate the technical drawbacks associated with SMO that are performed free-hand, but their accuracy has not been investigated. Therefore, we aimed to perform a pre- vs post-operative comparison to assess the accuracy of PSI in the setting of SMO correction.

Methods:

Eighteen patients (mean age = 47 ± 13.5 years) who underwent SMO with a PSI were prospectively recruited in a pre-post comparative study design. Inclusion criteria were correction of supramalleolar ankle varus or valgus deformity by a closing wedge SMO. Exclusion criteria consisted of biplanar SMO that required associated free-hand osteotomies. Clinical outcomes were collected by the American Orthopaedic Foot & Ankle Society (AOFAS), European Foot and Ankle Society (EFAS), and visual analogue scale (VAS) scores. Apart from the standard weightbearing radiographs, a weightbearing CT was performed to generate corresponding 3-dimensional (3D) bone models and measure the lateral distal tibia angle (LDTA) as main radiographic parameter.

Results:

The pre-operative radiographic parameters of the tibia joint alignment in patients with ankle varus (n = 12) deformity (LDTA_var = 96.5° ± 4.5°) and valgus (n = 6) deformity (LDTA_valg = 82.4° ± 2.5°) improved significantly relative to their post-operative equivalents (LDTA_var = 90.2° ± 3.2°); LDTA_valg = 90.9° ± 0.8°; P < .05). The pre-operative clinical outcome scores (AOFAS = 52.7 ± 22.9, EFAS = 15.1° ± 7.91°, VAS = 5 [2-8]) improved significantly relative to their post-operative equivalents (AOFAS = 75.5 ± 19.6; EFAS = 19° ± 7.6°; VAS = 3 [0-8]; P < .05). The mean simulated correction differed from the mean post-operative achieved correction within 1° (mean = 0.4°; range 0.1°-0.8°).

Conclusion:

This study demonstrated an accurate correction of distal tibia deformities by SMO using PSIs. The achieved post-operative correction differed within the range of 1° from the pre-operatively simulated correction. This indicates that PSIs provide a precise execution of the pre-operative planning. Future studies should assess the added value of performing an SMO with PSI compared with former free-hand techniques towards clinical and radiographical outcomes.

Graphical Abstract

This is a visual representation of the abstract.

Keywords

supramalleolar osteotomy patient-specific instrument weightbearing CT 3D measurement

Level of Evidence: Level II, prospective comparative study.

Introduction

Intra- or extra-articular deformities of the distal tibia can be effectively corrected by a supramalleolar osteotomy (SMO).^1
-11 The post-operative outcome is associated with relief of ankle pain and improvement of function in the short and long term.^12
-14 Despite these beneficial results, the amount of surgical correction is challenging to titrate and the procedure remains technically demanding.^15,16 At present, the amount of deformity correction is determined on plain radiographs using mathematical calculations.^17,18 However, there might occur a mis-match between the pre-operative radiographic planning and the pre-operative free-hand execution of an SMO. This could be attributed to a different position of the osteotomy on the distal tibia or to inconsistencies in the osteotomy wedge size, which can result in an over- or undercorrection in the coronal plane and can even cause secondary deformity in the sagittal plane through alteration of the distal tibial slope. Similar challenges have been reported across other osteotomy procedures within orthopaedic surgery, which has led to the development and implementation of patient-specific instruments (PSIs).^19
-22 This technology involves the production of customized surgical instruments through 3D printing, guided by pre-operative imaging and planning based on the patient’s specific anatomy.²³ Several studies have shown that PSIs are both accurate and safe during the execution of corrective osteotomies.^21,24,25 More specifically, in the ankle joint, PSIs have mainly been applied in the setting of total ankle replacement, where they demonstrated precise and reproducible results.^26,27 Despite these beneficial results, their usage in the setting of SMO has only been reported in small case series or out of the standard orthopaedic literature.^28,29 The limited number of SMO studies could be attributed to the technically demanding process of PSI generation, requiring deformity correction to be planned on weight-bearing radiographs and subsequently translated to 3-dimensional (3D) models derived from supine CT scans.³⁰ The introduction of weight-bearing CT (WBCT) has allowed for 3D bilateral foot and ankle imaging during physiological stance, which has the potential to streamline this workflow.^31
-33 Moreover, several studies have demonstrated a high reliability of translating standard 2D ankle and hindfoot alignment measurements to their 3D equivalents.^34,35 By virtue of these technical advancements, the former 3D SMO planning procedure that required 2 imaging modalities can now be performed in a 1-step process, where both the deformity correction and PSI acquisition on the bone model of the distal tibia require only a single imaging modality.³⁰ However, this stepwise process of a 3D WBCT-based pre-operative planning and PSI manufacturing has only been investigated in a pilot study limited to dome-shaped SMO.²⁸ Therefore, we aimed (1) to investigate the accuracy of a post-operative 3D distal alignment correction by comparing the achieved to the planned correction in a larger cohort of patients who underwent several types of SMO by a PSI and (2) to evaluate the functional outcomes by foot and ankle–specific scoring scales. The hypothesis of this study was that performing an SMO with PSI results in an accurate and precise correction of the distal tibia alignment with good or satisfactory patient-reported functional outcomes

Material and Methods

Study Population and Design

This prospective observational study was conducted in accordance with the Declaration of Helsinki and the Guidelines for Good Clinical Practice at Ghent University Hospital after approval from the institutional review board (no. B6702022000639). All participants provided written informed consent prior to inclusion. Patients were enrolled between January 2023 and July 2025 according to the following inclusion criteria: adults aged 18-70 years, ankle varus deformity (LDTA >92°-94°) or valgus (LDTA <85°-87°), scheduled for an anterolateral or medial closing wedge SMO with a correction of ≤10° and WBCT imaging pre- as well as post-operatively. Exclusion criteria consisted of inflammatory arthritis, insufficient imaging quality, biplanar SMOs, intra-articular SMOs (plafond plasty) and deformity proximal to the distal one-third of the tibial length (Figure 1). In total, 18 patients with a mean age of 47 ± 13.5 years were confirmed eligible and analyzed in a prospective pre-post study design before and after supramalleolar osteotomy (Table 1). Of those, 12 patients were corrected by a closing wedge osteotomy for distal tibia varus and 6 for valgus deformity. Clinical assessment of this cohort was based on the ankle range of motion (ROM) measured by a goniometer and pain, rated using a visual analogue scale (VAS) ranging from 0 (no pain) to 10 points (maximal pain). In addition, the European Foot and Ankle Society (EFAS) score ranging from 0 (maximal functional impairment) to 24 points (no functional impairment) and the American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot score ranging from 0 (maximal functional impairment) to 100 points (no functional impairment) and was assessed at each visit.^36,37 The VAS and EFAS scores were used as primary clinical outcome measures, and the AOFAS score as a comparative outcome measure. The clinical examination was done by research associates who were otherwise not involved in the treatment. Radiographic assessment involved plain weightbearing radiography as first-line imaging (Figure 2). An anteroposterior (AP), posterior-anterior (PA, Saltzman), lateral and dorsal-plantar (DP) view of the foot and ankle were obtained. Ankle OA was classified by a fellowship trained foot and ankle surgeon (A.B.) according to the Takakura classification on AP weightbearing radiographs of the ankle (Table 1).² Additional WBCT imaging was obtained pre-operatively and post-operatively between 3 and 6 months, as part of the routine imaging protocol for supramalleolar osteotomy correction at our institution.

Figure 1.

Flowchart of the study enrollment process.

Table 1.

Baseline Demographic, Radiographic Information and Associated Procedure.

Characteristic	Prevalence
SMO closing wedge: varus/valgus, n	12/6
Age, y, mean ± SD (range)	47 ± 13.5 (22-64)
Gender: male/female, %	71.4 / 28.6
Etiology: post-traumatic/constitutional, %	78.6 / 21.3
BMI, mean (range)	27.7 (22.0-35.0)
Takakura stage of ankle osteoarthritis, n/n (%)
Stage 0	0/18 (0)
Stage 1	7/18 (39)
Stage 2	8/18 (44)
Stage 3a	3/18 (16)
Stage 3b	0/18 (0)
Stage 4	0/18 (0)
Fibula osteotomy	13
Calcaneus osteotomy	1
Osteotomy first cuneiform base	1
Subtalar fusion	0
Ligament reconstruction	2
Peroneus longus to brevis transfer	0
Tibialis posterior tendon revision	0
OCD treatment	4

Abbreviations: BMI, body mass index; OCD, osteochondral dissecans; SMO, supramalleolar osteotomy.

Figure 2.

Overview of the 3D measurements. (A) Selection of the landmarks on the proximal tibia to determine the center of the lateral and medial tibial plateau (left). The center of the tibial plateau was determined as the middle between the center of the lateral and medial tibial plateau (center) and projection of the bimalleolar axis on the tibial plafond to determine the center of the ankle joint middle (right). (B) Quantification of the lateral distal tibial angle (LDTA) by intersecting the mechanical tibia axis in the coronal plane (connection between center of the tibial plateau with the center of the ankle) and the coronal distal tibia joint line axis (left). Calculation of the anterior distal tibia angle (ADTA) by intersecting the mechanical tibial axis in the sagittal plane (connecting the middle of the tibial plateau with the middle of the articular surface of the distal tibia) and the sagittal distal tibia joint line axis (middle). Computation of the tibial torsion (TT) by intersecting the central axis of the tibial plateau with the bimalleolar axis of the ankle.

Pre-operative planning and PSI manufacturing

WBCT imaging was performed using a HiRise scanner (Curvebeam) in a fully upright weightbearing position with both feet at the natural resting stance and positioned at the same height on the circular weightbearing platform of the imaging device. Following image acquisition protocol: 0.2-mm slice thickness, 1-mm slice, and 1.5-mSv effective radiation dose per scan. Corresponding 3D bone models were reconstructed after selecting an image stack in DICOM format using D2P software (Octon). Once the image stack is loaded, the software automatically renders a 3D isosurface of the bone. Anatomical landmarks on the proximal tibia and distal tibia and fibula were selected by the third author (A.B., biomedical engineer). Based on these axes following measurements were acquired by the software: lateral distal tibia angle (LDTA), anterior distal tibial angle (ADTA), tibial torsion (TT) angle to determine the tibia alignment (Figure 2A and B). The LDTA was defined by intersecting the mechanical tibia axis with the axis of the tibial plafond in the coronal plane (LDTA; normal values, 89° ± 3°).³⁸ The ADTA was determined by measuring the angle between the mechanical axis of the tibia and the sagittal axis of the tibial plafond (ADTA; normal values, 83° ± 3.6°).³⁹ The tibial torsion was calculated by intersecting the central axis of the tibial plateau and the intermalleolar axis (TT, normal range, 24°-30°).⁴⁰ Previous studies reporting these computed 3D measurements using the same or other software have demonstrated high intra- and inter-observer reliability for angular measurements used in this study.^34,35,41
-44 Specifically, for the tibial alignment, the reported reliability coefficients were ICC_inter = 0.86 and ICC_intra = 0.89, which corresponded to a near perfect agreement.⁴⁵ The ADTA and TT were used to rule out any additional sagittal or axial plane deformity. The LDTA served as a primary reference parameter for 3D deformity planning and the planned correction aimed to normalize it according to established physiological values. The PSIs were designed based on the pre-operative 3D deformity planning from the engineering team (Newclip Technics). The pre-operative deformity planning was primarily performed using the center of rotation of angulation (CORA) as the reference point.^38,46 However, when the CORA was too close to the tibiotalar articulation in the epiphyseal area (defined within 2 cm from the joint line)⁴⁷ or above the metaphyseal area (defined as more than 4-6 cm measured from the joint line),⁴⁸ the osteotomy would be located in the metaphyseal are approximately 5 cm from the tip of the medial malleolus.⁴ Additionally, the pre-operative planning was also designed to have the osteotomy as close as possible to the suprasyndesmotic area or “safe zone.”⁴⁹ As the WBCT scan was able to assess the entire lower limb alignment, the pre-operative deformity alignment analysis report was also able to quantify the hip-knee-ankle. This radiographic parameter is used at our institution to have an initial lower limb alignment analysis. In general, patients were referred to the orthopaedic knee service when SMO was being considered and the hip-knee-ankle angle exceeded 5° of varus or valgus. However, in case of post-traumatic distal tibia deformity, we would restore the original alignment first and then refer the patient to the knee surgeon in case symptomatic residual knee malalignment was observed. The PSI consisted of a personalized cutting block and was made of Fine Polyamide PA 2200 (EOS GmbH–Electro Optical Systems) using 3D printing and were steam sterilized (270 °F; exposure time, 4 minutes; drying time, 20 minutes).⁵⁰

On the post-operative WBCT scans, the same 3D measurements were performed and compared to their equivalents calculated in the pre-operative planning report.

Surgical Technique

Medial and lateral closing wedge supramalleolar osteotomies in this cohort were performed by the senior author (A.B., fellowship-trained foot ankle surgeon) in accordance with previously published protocols (Table 1).^28,51

Surgery was performed under combined anesthesia containing a popliteal nerve block and subsequent general anesthesia. The patient was positioned supine, with a sandbag placed beneath the thigh to align the foot in a straight position, ensuring that the longitudinal axis of the foot was perpendicular to the floor. A direct anterior approach was performed using the interval between the tibialis anterior and extensor hallucis tendon to expose the tibia for the lateral closing wedge and a longitudinal medial incision for the medial supramalleolar closing wedge osteotomy. The PSI consisted of a customized cutting guide block, which incorporates the preoperatively calculated wedge size required for correction during the SMO. After exposure of the distal tibia, the PSI was applied and positioned according to the native bony contours (Figure 3). K-wires of 2 mm were applied in dedicated sleeves of the PSI to maintain its correct position on the distal tibia, which was verified using fluoroscopy. In an anterolateral closing SMO to correct ankle varus deformity, 2 osteotomies are performed as part of the standard procedure, 1 on the tibia and 1 on the fibula. Once the tibial wedge is completed, it is left in situ to leave some stability before performing the fibula osteotomy. The addition of a fibular osteotomy is necessary to avoid difficulties in reducing the tibia. As a rule of thumb, the size of the wedge on the fibula was approximately half of that on the tibia, except for posttraumatic deformities of the fibula. In this situation, the correction depended on the amount and type of fibular malalignment. In case of a medial closing wedge SMO for ankle valgus deformity, a fibular osteotomy was not part of the standard procedure. However, in 1 patient with ankle valgus deformity, it was required because of a post-traumatic shortening of the fibula. Following removal of the wedge in both anterolateral or medial closing wedge SMOs, two 2-mm crossed K-wires are being positioned in place before the closing of the tibial osteotomy. This step is performed manually by applying a lateral or medial force on the heel or assisted using a Hintermann compressor (Integra LifeSciences) when needed to allow for a gradual compression/closing of the osteotomy. After closing of the osteotomy, the 2 K-wires are drilled through the cortex to preliminary fixate the osteotomy. Afterward, a definite fixation is performed using a lateral or medial distal tibia osteotomy plate (Newclip Technics). Postoperatively, all patients were immobilized in a non–weight-bearing cast for the first 6 weeks. A wound check and plaster exchange were performed at 2 weeks, followed by a subsequent plaster exchange at 4 weeks. At 6 weeks postoperatively, patients underwent clinical and weight-bearing radiographic evaluation. When early signs of callus formation were evident on imaging, patients were allowed to initiate a supervised progressive weight-bearing protocol using a walker boot, under guidance of a physiotherapist. Weight-bearing was gradually increased over a 6-week period, progressing from 25% to 50%, 75%, and ultimately full body weight. At 3 months postoperatively, radiographic assessment included weight-bearing CT to evaluate both correction and bone union, defined as callus bridging across at least 3 of 4 cortices. Once radiographic union was confirmed, the walker boot was discontinued.⁵²

Figure 3.

(A) Overview of the peri-operative placement of the patient-specific instrument. (B) Dissection of the distal tibia in a patient with ankle varus deformity. (C) Positioning of the patient-specific guide. (D) Pre-operative planning of the patient-specific instrument (PSI) 12 mm from the articular surface. (E) Fixation of the patient-specific guide with Kirschner (K) wires. (F) Dissection of the distal tibia in a patient with ankle valgus deformity. (G) Positioning of the patient-specific guide. (H) Pre-operative planning of the patient-specific guide 26 mm from the tip of the medial malleolus. Fixation of the PSI with k-wires.

Statistical analysis

An a priori power analysis was performed using R-package pwr based on effect size (Cohen d) calculated using previously reported pre- and postoperative data (TAS, TTS, Tilt) in varus patients treated by a supramalleolar osteotomy.⁸ A total sample size of 12 (6 per group) needs to be achieved when comparing 2 groups for the calculated effect size (f = 1.5) with a power level of 0.80 and a level of significance set at .05.¹² Shapiro-Wilk tests were used to assess whether the data were normally distributed.

The Mann-Whitney U test for 2 independent samples with 95% CI was used to evaluate the differences between 2 variables, 1-way analysis of variance between more than 2 variables, and multiple linear regressions for relationships. The paired Student t test was used to estimate evolution of functional outcomes during follow-up. The differences in proportions between 2 samples were estimated with the z test with 95% CI.

Results

Radiographic Outcomes

Tibia Alignment

In patients with ankle varus deformity, the pre-operative coronal alignment (LDTA = 96.5° ± 4.5°) improved significantly post-operatively (LDTA = 90.2° ± 3.2°) after supramalleolar osteotomy (P < .05; Table 3). The pre-operative sagittal and axial alignment (ADTA = 82.9° ± 3.9°; TT = 28.8 ± 9.8°) did not improve significantly post-operatively (ADTA = 83.8 ± 3.8; TT = 29.2 ± 9.8°) after supramalleolar osteotomy (P < .05; Table 2; Figure 4).

Table 2.

Preoperative and Postoperative Radiographic Outcome.

Deformity	Radiographic Angle,degrees (Mean ± SD)	Pre-operative(95% CI)	Post-operative(95% CI)	Difference in Planned vs Achieved Correction		AdjustedP Value ^a
Deformity	Radiographic Angle,degrees (Mean ± SD)	Pre-operative(95% CI)	Post-operative(95% CI)	Mean	Range	AdjustedP Value ^a
Varus	LDTA	96.5 ± 4.5 (94.0-99.0)	90.2 ± 3.2 (88.4-92.0)	0.4	0.1-0.8	<.01
	ADTA	82.9 ± 3.9 (79.8-86.0)	83.8 ± 3.8 (80.8-86.8)			.014
	TT	28.8 ± 9.8 (21.0-36.6)	29.2 ± 9.8 (21.4-37.0)			.4
Valgus	LDTA	82.4 ± 2.5 (80.4-84.4)	90.9 ± 0.8 (90.4-91.4)	0.5	0.4-0.8	<.01
	ADTA	84.5 ± 6.6 (79.2-89.8)	85.0 ± 7.4 (79.1-90.9)			.015
	TT	28.5 ± 9.3 (21.1-35.9)	26.8 ± 7.3 (21.0-32.6)			.25

Abbreviations: ADTA, anterior distal tibia angle; LDTA, lateral distal tibia ankle; TT, tibial torsion.

Significant values are marked in bold.

Figure 4.

Radiographic overview of a patient with ankle varus deformity corrected by a lateral closing wedge SMO. (A) Pre-operative deformity from left to right: AP view demonstrating varus deformity of the distal tibia and medial joint space degeneration,posterior-anterior (PA, Saltzman) view depicting varus deformity of the distal tibia, lateral view demonstrating no sagittal plane deformity and Weightbearing CT demonstrating varus deformity of the distal tibia and medial joint space degeneration. (B) Post-operative correction from left to right: AP view demonstrating correction of varus deformity by SMO of the distal tibia, Saltzman view demonstrating correction of varus deformity by SMO, Lateral view demonstrating no sagittal plane deviations after SMO and weightbearing CT demonstrating correction of varus deformity by SMO. AP, anterior-posterior; SMO, supramalleolar osteotomy.

In patients with ankle valgus deformity, the pre-operative coronal alignment (LDTA = 82.4° ± 2.5°) improved significantly post-operatively (LDTA = 90.9° ± 0.8°) after supramalleolar osteotomy (P < .05; Table 3; Figure 5). The pre-operative sagittal and axial alignment (ADTA = 84.5° ± 6.6°; TT = 28.5° ± 9.3°) did not improve significantly post-operatively (ADTA = 85.0° ± 7.4°; TT = 26.8° ± 7.3°) after supramalleolar osteotomy (P < .05; Table 3). The mean simulated correction differed from the mean post-operative achieved correction within 1° (mean = 0.4°; range 0.1°-0.8°; Table 2; Figure 6). At 3 months, all patients demonstrated radiographic union on WBCT, defined by the presence of bridging callus across ≥3 cortices on coronal and sagittal slices.

Table 3.

Preoperative and Postoperative Clinical Outcome.

Variable	Pre-operative	Post-operative	Difference		Adjusted P Value^a
Variable	Pre-operative	Post-operative	Estimate	95% CI	Adjusted P Value^a
AOFAS score, mean ± SD	52.7 ± 22.9	75.5 ± 19.6	16	9 to 23	<.05
EFAS score, mean ± SD	15.1 ± 7.9	19 ± 7.6	16	9 to 23	<.05
Pain on VAS, median (range)	5 (2-8)	3 (0-7)	–1.5	–0.6 to −2.4	<.01
ROM, degrees, mean ± SD	44 ± 15	45 ± 17	–0.5	4.1 to −5.0	.80

Abbreviations: AOFAS, American Orthopaedic Foot & Ankle Society; EFAS, European Foot and Ankle Society; ROM, range of motion; VAS, visual analogue scale.

Significant values are marked in bold.

Figure 5.

Radiographic overview of a patient with ankle valgus deformity a medial closing wedge SMO. (A) Pre-operative deformity from left to right: AP view demonstrating valgus deformity of the distal tibia and medial joint space degeneration, Saltzman view depicting valgus deformity of the distal tibia, Lateral view demonstrating no sagittal plane deformity and Weightbearing CT demonstrating varus deformity of the distal tibia and medial joint space degeneration. (B) Pos-operative correction from left to right: AP view demonstrating correction of valgus deformity by SMO of the distal tibia, Saltzman view demonstrating correction of valgus deformity by SMO, Lateral view demonstrating no sagittal plane deviations after SMO and weightbearing CT demonstrating correction of valgus deformity by SMO. AP, anterior-posterior; SMO, supramalleolar osteotomy.

Figure 6.

Overview of the planned vs achieved correction of the distal tibia by SMO using a PSI. (A) Patient with a pre-operative varus deformity of the distal tibia and sequential depiction of the virtual planned correction, post-operative achieved correction and overlay between the virtual planned correction (green) and post-operative achieved correction (white). (B) Patient with a pre-operative valgus deformity of the distal tibia with sequential depiction of the virtual planned correction, post-operative achieved correction and overlay between the virtual planned correction (green) and post-operative achieved correction (white). PSI, patient-specific instrument; SMO, supramalleolar osteotomy.

Clinical Outcomes

The pre-operative pain (VAS = 5, range: 2-8) and function scores (EFAS = 15.1° ± 7.91°; AOFAS = 52.7 ± 22.9) improved significantly compared to the post-operative pain (VAS = 3; range: 0-7) and function (EFAS = 19° ± 7.6°; AOFAS = 75.5 ± 19.6) after supramalleolar osteotomy (P < .05; Table 3). No significant differences could be found for motion of the ankle joint pre-operatively (ROM = 44° ± 15°) compared with post-operatively (ROM = 45° ± 17°; P > .05; Table 3). Regarding the post-operative complications, we had 2 superficial wound complications, 1 hematoma, and 3 neuropathies (Table 4). Despite overall improvement in clinical outcomes across the cohort, 2 patients underwent ankle arthrodesis, because of a post-operative arthrofibrosis (n = 1) and pain relief that was insufficient (n = 1).

Table 4.

Summary of Complications and Revision Surgery.

Complication / Revision Procedure	Count
Delayed union	1
Deep infection	0
Re-osteotomy	0
Implant removal	1
Hinge fracture	1
Superficial wound complication	2
Hematoma	1
Neuropathy	3
Total ankle replacement	0
Ankle arthrodesis	2

Discussion

This study investigated the pre-operatively planned vs post-operatively achieved alignment correction after PSI-assisted SMO and reported its associated clinical outcome. The principal findings demonstrated that the difference between the pre-operatively planned and post-operatively achieved radiographic alignment was within the range of 1° and that the clinical outcomes were good to excellent.

Regarding the radiographic outcome, our results demonstrated an accurate correction of the distal tibia alignment measurements toward normal values reported in the literature.^38,53,54 These findings parallel 3 previously published reports that examined the use of PSI in SMO procedures.^28,29,55 In these studies, the authors could also demonstrate an accurate correction of the pre-operative relative to the post-operative alignment in a cohort of tibia plafond plasties,⁵⁵ opening wedge,²⁹ and dome-shaped²⁸ osteotomies in distal tibia varus deformity in retrospective study designs. Our study contributes to these former reports by prospectively investigating a cohort of closing wedge SMO in both distal tibia varus and valgus deformities. These types of SMO are also frequently used in clinical practice for both distal tibia varus and valgus deformities,^56,57 but we could not identify studies using PSI during these types of corrections. This study is also the first to provide pre-operative planning on the entire 3D tibia axis derived frow weightbearing CT imaging. Stufkens et al⁵³ previously demonstrated that using the full tibial axis in radiographic planning provides a more accurate representation of tibial alignment, whereas short tibial views produced significantly deviating values.

The study from Faict et al²⁸ was the only study to report the deviation from the planned vs the achieved correction and found that the predicted radiologic outcome was achieved with a maximum error of 2°. Our study found that the targeted outcome was achieved within a variance of 1°. This improved precision could potentially be attributed to the PSI system, which consisted in their system of 2 distinct parts, one part served as drilling guide and the second part was used as a reduction guide.²⁸ In this study, the PSI consisted of one block containing both the cutting and reduction of the osteotomy, which could potentially leave less variation in the osseous correction after the SMO. However, the obtained accuracy should be interpreted in light of the reported measurement variability that fell within an ICC_inter of 0.86 and an ICC_intra of 0.89, during the computed analysis. In larger cohort series, this could potentially create more variance. Overall, these results are within the accuracy range of other orthopaedic osteotomy procedures such as the knee (high tibial osteotomies) or wrist (distal radius osteotomies), in which postoperative correction is typically within 1° to 2° of the planned correction.^25,58 Of note, this study used the mechanical tibia alignment, defined by the lateral distal tibia angle to perform the pre-operative planning. However, several studies have demonstrated the importance of taken in to account the lower-limb axis when planning SMOs.⁵⁹ For this reason, future studies could further improve pre-operative planning by incorporating the full lower-limb alignment and compare the pre-operative planning of a PSI based on mechanical tibia alignment to give guidelines regarding which method would be preferable for which type of deformities. Post-operatively, this approach may also provide further insight into how translational at the osteotomy site would influence the overall lower-limb alignment when the SMO is performed away from the CORA.

Regarding the clinical outcome, all patients obtained significant improvement in VAS, AOFAS, and EFAS scores at a mean follow-up period of 13.2 months. These results are in line with previous studies reporting the short-term outcome of SMO surgery.^12,29,60 In this light, the reported short-term clinical outcome do not present superiority over supramalleolar osteotomies performed without PSI. However, the radiologic outcome data demonstrated less variability toward achieving the obtained normal alignment of the ankle joint. In the long term, this could potentially be beneficial for the cartilage loading and improve the survival rate of supramalleolar osteotomies. However, this aspect needs to be confirmed in subsequent studies with long-term follow-up using both clinical and radiological outcome data. It should also be taken into account that the AOFAS score was not used as a primary outcome measure, but rather as a comparative measure to place the clinical outcomes of this study into perspective with other SMO studies, as advised by the AOFAS position statement.⁶¹ However, a recent study in patients with ankle OA demonstrated that the patient-reported component of the AOFAS score represents a valid and reliable measurement construct, which could potentially be used in future ankle OA studies.⁶² Despite overall improvement in clinical outcomes across the cohort, 2 patients underwent ankle arthrodesis, The first patient developed a postoperative ankle arthrofibrosis. The second patient presented with associated iatrogenic cartilage damage following multiple prior surgical procedures performed at another institution. Both patients were corrected by an anterolateral closing wedge SMO and demonstrated postoperative pain improvement, but this remained insufficient for the patient. Therefore, it was decided after repeated clinical follow-up visits to perform an ankle arthrodesis. Of note, despite improving accuracy, one of the main concerns of patient-specific guides is related to wound complications.⁶³ However, we had only one wound complication, which was in the same range as in the literature and could be attributed to the compactness of newer-generation guides.^60,64

This study encountered several limitations. First, we report on a relatively small study population, which could impair the generalizability of the findings. However, we could demonstrate effective outcomes of the performed corrections, and the patient number of this cohort exceeds those from previous SMO studies using PSI systems. Second, the longest follow-up was only 29 months and therefore we cannot present any mid- or long-term results. Nonetheless, our short-term complications and obtained alignment are in the range of those of previous studies,⁶⁰ which may suggest that the long-term results would be in a comparable range.¹³ Third, the preoperative planning remains time-consuming and often necessitates specialized engineering support, with considerable costs associated with PSI production and weight-bearing CT imaging systems. The acquisition and maintenance of weight-bearing CT scanners represent a substantial financial investment, and PSI manufacturing further adds to procedural costs. However, weight-bearing CT systems are based on cone-beam CT technology, which is inherently less expensive than conventional multidetector CT scanners, and recent advances in automated segmentation and lower-limb deformity analysis facilitate efficient generation of 3D models. In parallel, the increasing availability of 3D printing services has progressively reduced PSI manufacturing costs.^65,66

In conclusion, supramalleolar osteotomies are effective procedures to correct distal tibia deformities.^1
-11 However, the surgery remains technically demanding and is often limited by a 2D radiographic planning of a 3D deformity. For this reason, we implemented weight-bearing CT imaging to plan a 3D deformity correction using PSIs. This approach contained both an accurate outcome by providing radiographic outcomes within those of normal values and precise results by demonstrating an achieved correction within the range of 1° from the planned correction. However, mid- to long-term and comparative prospective studies are required to confirm the initial promising findings. Additionally, it should be evaluated, preferably in a randomized trial, whether usage of PSI during SMO yields potential other benefits such as an improvement in surgery time, lower-limb axis, peri-operative radiation exposure, and patient-reported outcomes, which could outweigh the additional costs of the PSIs.

Supplemental Material

sj-pdf-1-fai-10.1177_10711007261434977 – Supplemental material for Accuracy of Patient-Specific Instruments for Supramalleolar Osteotomies

Supplemental material, sj-pdf-1-fai-10.1177_10711007261434977 for Accuracy of Patient-Specific Instruments for Supramalleolar Osteotomies by Cédric Bonte, Jules Rasschaert, Juliette L’Herroux, Ir, Matthias Peiffer, Nicola Krähenbühl, Kristian Buedts, Emmanuel Audenaert and Arne Burssens in Foot & Ankle International

Footnotes

Author Note

The investigation was performed at Ghent University Hospital, Ghent, Belgium.

ORCID iDs

Cédric Bonte, MD,

Matthias Peiffer, MD, PhD,

Nicola Krähenbühl, MD,

Kristian Buedts, MD,

Arne Burssens, MD, PhD,

Ethical Considerations

Ethical approval for this study was obtained from the Commission of Medical Ethics from the Ghent University Hospital, Ghent, Belgium (approval number/ID: B6702022000639).

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by a Mobility Research Grant from the Research Foundation–Flanders (V424118, FWO).

Declaration of Conflicting Interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Kristian Buedts, MD, reports disclosures relevant to manuscript of Stryker, Acumed, Newclip, Artrhex, Permedica, and general disclosures of consultancy for Newclip. Emmanuel Audenaert, MD, PhD, reports disclosures relevant to manuscript of Senior Clinical Investigator Fellowship Grant from the Research Foundation–Flanders (1842619N, FWO). Arne Burssens, MD, PhD, reports disclosures relevant to manuscript of CurvebeamAi, Newclip, and Surgebright and general disclosures of consultancy for CurvebeamAi and course lectures for Newclip. Disclosure forms for all authors are available online.

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