Abstract
Background
Obesity contributes to the accelerated progression of knee osteoarthritis. Medial open-wedge high tibial osteotomy (MOWHTO) is a joint-preserving surgical intervention for unicompartmental knee osteoarthritis; however, its efficacy in patients with obesity remains controversial. This study aimed to evaluate the 5-year clinical and radiographic outcomes of MOWHTO with lateral supplemental lag screw fixation in patients with obesity.
Materials and methods
This retrospective cohort study included patients with obesity who underwent MOWHTO between 2017 and 2020, with a minimum follow-up of 5 years. All procedures were performed by a single surgeon using three-dimensional printed, patient-specific instrumentation, locking plates, and a lateral supplemental lag screw. Clinical outcomes were assessed using the visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Radiographic parameters, including the weight-bearing line percentage (WBL%) and medial proximal tibial angle (MPTA), were evaluated.
Results
Significant improvements in VAS and WOMAC scores were observed at all postoperative time points (p < 0.001) and were accompanied by improved radiographic alignment, with WBL% shifting toward the Fujisawa point and increased MPTA values. At 5 years, mild regression in alignment was noted; however, the overall correction was maintained. The 5-year conversion rate of TKA was 3.8%. Lateral hinge fractures occurred in 3.8% of cases and healed without loss of correction.
Conclusions
Medial open-wedge high tibial osteotomy is associated with satisfactory 5-year clinical and radiographic outcomes in patients with obesity. Obesity is not necessarily a contraindication for HTO, although appropriate patient selection and long-term follow-up are essential for this procedure.
Level of evidence: III, Retrospective cohort study.
Keywords: High tibial osteotomy, Obesity, Medial compartment osteoarthritis, Knee alignment, Patient-specific instrumentation, Total knee arthroplasty
Introduction
Obesity is a global public health concern. It not only increases the risk of chronic conditions such as cardiovascular disease and diabetes but also imposes a substantial burden on the musculoskeletal system [1]. As in other systemic diseases, obesity has been shown to lead to a faster progression of osteoarthritis [2]. In individuals with obesity, excessive body weight increases the mechanical load on the knee joints, leading to an acceleration of cartilage wear and degeneration over time [3]. Furthermore, adipose tissue releases pro-inflammatory cytokines that contribute to the progression and worsening of osteoarthritis [4–6]. For young patients with obesity aged < 65 years with isolated medial compartment knee osteoarthritis on a stable knee with a full range of motion, medial open-wedge high tibial osteotomy (MOWHTO) may serve as an acceptable joint-preserving option [7]. The role of obesity as a potential contraindication for high tibial osteotomy (HTO) has long been controversial [8–13]. However, there is a relative paucity of literature evaluating the clinical impact of modern fixation techniques, such as locking plate systems, in the setting of HTO [14]. With advancements in surgical techniques and the increasing use of contemporary fixation methods, including rigid locking plate systems and supplemental fixation, the outcomes of patients with obesity undergoing high tibial osteotomy warrant reevaluation [15–17].
Based on the above findings, the primary aim of this study was to evaluate changes in functional outcomes and radiographic parameters before and after surgery in patients with obesity (body mass index [BMI] > 30 kg/m2) undergoing MOWHTO, as well as to assess the 5-year survivorship of the procedure, defined as the absence of conversion to total knee arthroplasty (TKA). The secondary aim was to assess procedure-related complications, including infection, implant failure, and lateral hinge fractures. We hypothesized that MOWHTO, performed with accurate correction, specialized locking plates, and a lateral supplemental lag screw, would be a safe and effective treatment option for patients with obesity.
Materials and methods
Data collection
This study was approved by the Institutional Review Board, and written informed consent was obtained from all participants before enrollment.
The study enrolled patients with isolated medial-compartment knee osteoarthritis who underwent MOWHTO between 2017 and 2020. All surgeries were performed by the same senior surgeon (C.S.Y.) at a tertiary referral medical center. A single-surgeon study design was selected to ensure consistency in surgical techniques, standardization of clinical decision-making, and uniformity in patient selection criteria. The inclusion criteria were as follows: (1) patients aged < 75 years with a history of isolated medial compartment knee osteoarthritis with varus deformity, and (2) patients who underwent MOWHTO with a minimum follow-up of 5 years. The exclusion criteria were concomitant knee injuries such as ligamentous injuries and periarticular fractures, infection, previous tumors, knee instability, knee stiffness with a range of motion of less than 100°, any prior injury or surgery of the ipsilateral lower extremity, and insufficient follow-up of less than 5 years. Patients older than 75 years were also excluded because HTO is rarely performed in this age group at our institution, and TKA is generally preferred because of considerations related to postoperative rehabilitation and implant longevity.
All patients were diagnosed preoperatively by physical examination and imaging. Routine preoperative and postoperative standing anteroposterior (AP) radiographs of the entire lower extremity and standing knee AP and lateral views were obtained. The 1-mm slice separation lower limb computer tomography scans were routinely arranged to customize the three-dimensional (3D)-printed patient-specific instrument (PSI) guide. Patient demographic data were obtained from medical records, and postoperative functional outcomes were assessed during outpatient follow-up using the visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaires [18, 19]. The radiographic angles were measured using preoperative and postoperative standing AP radiographs of the whole lower extremities. The measured parameters included the Kellgren–Lawrence grade, weight-bearing line ratio (WBL%), hip–knee–ankle angle (HKA), medial proximal tibial angle (MPTA), anatomical lateral distal femoral angle (aLDFA), and joint line convergence angle (JLCA) [20]. Except for the HKA, all other angular measurements were obtained from standing AP and lateral knee radiographs, as full-length lower-limb radiographs are more susceptible to errors related to patient positioning and radiographic magnification [21]. WBL% is defined as the percentage of the tibial plateau width through which the mechanical axis passes relative to the medial edge of the tibial plateau [22]. The HKA was defined as the angle formed by the mechanical axis of the femur and tibia, with 180° representing neutral alignment, values greater than 180° indicating valgus alignment, and values less than 180° indicating varus alignment. The MPTA was defined as the medial angle between the tibial plateau and the anatomical axis of the tibia. aLDFA was defined as the lateral angle between the distal femoral joint line and the anatomical axis of the femur. The JLCA was defined as the angle between the femoral and tibial joint lines, reflecting the intra-articular alignment. All radiographic measurements were independently performed by two orthopedic residents (Y.H.T. and K.H.L.), and the average of the measurements was used for the analysis. The reliability of radiographic measurements was assessed using intraclass correlation coefficients (ICCs). Interobserver reliability was determined based on measurements obtained by the two independent observers, whereas intraobserver reliability was evaluated using repeated measurements. The interobserver and intraobserver ICC values ranged from 0.84 to 0.91, indicating good to excellent reliability. Implant failure was defined as mechanical or biological failure of the fixation construct, including loss of correction, hardware breakage (plate or screw), or nonunion, as identified on follow-up radiographs or clinical evaluation. The lateral hinge fractures were classified according to the Takeuchi classification system [23, 24]. All demographic data were collected and organized.
The patients were divided into two groups for the analysis based on the World Health Organization definition: patients with a BMI between 30 and 40 kg/m2, and patients with morbid obesity (BMI > 40 kg/m2) for descriptive stratification of outcomes across different degrees of obesity [25]. Comprehensive evaluations, including functional scores and radiological parameters, were conducted 1, 3, and 5 years after the surgical procedure.
Preoperative planning
The preoperative plan was divided into two parts: two-dimensional (2D) and 3D. In the 2D component, the preoperative HKA angle, MPTA, and tibial slope were measured to determine the correction angle, opening wedge thickness, hinge point location, osteotomy direction, and depth. The lateral hinge was located superiorly to the fibular head. The cutting point was set at the most concave corner of the proximal tibia on the medial side. The postoperative goal was to shift WBL to pass through Fujisawa’s point (approximately 62.5% of the tibial plateau width) [26, 27]. MATLAB software (MathWorks Inc., Natick, MA, USA) was used to perform the necessary calculations. In the 3D planning component, a commercial 3D printer (Formlabs, Cambridge, MA, USA) was used with biocompatible resin (Dental SG, compliant with EN ISO 10993–1:2009/AC:2010 and USP Class VI standards). The printing process was based on calculations performed using the Amira v.4.0 software (Mercury Computer Systems, Inc., Berlin, Germany) [28]. The PSI cutting jig used intraoperatively and the lateral supplemental lag screw used for these patients are shown in Fig. 1.
Fig. 1.
Intraoperative and postoperative demonstration of medial open-wedge high tibial osteotomy using A, B a patient-specific instrumentation cutting jig, and C a lateral supplemental lag screw as seen on postoperative radiographs
Surgical technique and postoperative care
Surgeries were conducted under either general or spinal anesthesia, with the patients in a supine position. A longitudinal incision of approximately 7 cm was made over the anteromedial side of the proximal tibia to accommodate the PSI cutting jig. The soft tissue was carefully dissected to avoid damage to the deep medial collateral ligament. Selective release of the superficial medial collateral ligament was performed only when excessive medial tightness was encountered, which interfered with adequate correction. Adequate exposure of the anteromedial tibial surface and meticulous removal of the periosteum and surrounding soft tissues were essential to ensure proper seating of the jig. The PSI cutting jig was positioned under direct visualization and temporarily fixed with pins to ensure accurate fitting before osteotomy.
MOWHTO using a biplanar osteotomy technique was performed after verifying that the PSI cutting jig conformed precisely to the tibial surface and was secured with a specialized locking plate (TomoFix, Synthes GmbH, Switzerland, or Aplus High Tibial Osteotomy anatomical plate, Taiwan). In addition, a percutaneous 6.5-mm supplemental lag cannulated screw was inserted from the lateral side of the tibia to enhance implant stability in all cases (Fig. 1). The technique associated with the lateral supplemental lag screws has been described in detail in previous studies [29–31]. An adequate allograft was used to fill the bone defects. A 1/8 Hemovac drain was positioned postoperatively and removed on the second postoperative day. The position of the implants and the presence of any lateral hinge fracture were confirmed on immediate postoperative radiographs obtained in the recovery room.
On the day after surgery, patients began partial weight bearing, which was continued for 6 weeks. The patients were also instructed to perform quadriceps and hamstring strengthening exercises during rehabilitation. All patients were scheduled for follow-up visits at 2 weeks, 6 weeks, 3 months, and 6 months postoperatively. Annual follow-up visits were recommended in the absence of any specific discomfort or complications. Six weeks postoperatively, upon confirmation by radiographs obtained during the outpatient visits, the patients could ambulate with full weight bearing on the affected limb. If postoperative radiographs obtained in the recovery room revealed a lateral hinge fracture, patients were advised to refrain from weight bearing on the affected limb for another month. Follow-up radiographs were obtained to confirm callus formation in the fracture gap before initiating partial weight-bearing rehabilitation.
Statistical analysis
Statistical analyses were performed using SPSS software (v.25.0; IBM Corp., Armonk, NY, USA). Descriptive statistics, including medians, means, and standard deviations, were used to evaluate the data. Continuous variables were analyzed using paired t-tests. Statistical significance was set at p < 0.05. No imputation was performed for missing data, and all analyses were conducted using complete-case analysis.
Results
Demographics
From 2017 to 2020, the mean follow-up duration was 6.5 ± 1.0 years (range, 5.0–8.0 years). Four patients did not complete the minimum postoperative follow-up of 5 years and were therefore excluded from the final analysis. A total of 36 patients with a BMI between 30 and 40 kg/m2 (group A) and 12 patients with a BMI above 40 kg/m2 who completed a 5-year follow-up (group B) were included in the study. Of the 78 operated knees, 40 were fixed using TomoFix plates and 38 using Aplus plates. According to the radiographic assessment, 52 knees were classified as Kellgren–Lawrence grade II and 26 knees as grade III. Groups A and B included 63 and 15 MOWHTO cases, respectively. Apart from group A patients being relatively older (58.1 ± 7.9 years compared with 52.7 ± 11.8 years in group B) and having a higher proportion of bilateral surgeries (75% compared with 25% in group B), the baseline functional scores and preoperative radiographic alignment were generally comparable between the two groups. Detailed demographic data are presented in Table 1.
Table 1.
Patient demographic data
| Group A | Group B | |
|---|---|---|
| Patient number | 36 | 12 |
| Bilateral HTO N (%) | 27 (75.0%) | 3 (25.0%) |
| Female N (%) | 27 (75.0%) | 6 (50.0%) |
| Age (years) | 58.1 ± 7.9 (42-–74) | 52.7 ± 11.8 (35–70) |
| KL grade (II/III) | 41 (65.1%)/22 (34.9%) | 11 (73.3%)/4 (26.7%) |
| Preoperative VAS | 7.4 ± 0.9 (6–9) | 7.9 ± 1.2 (6–9) |
| Preoperative WOMAC | ||
| Pain | 17.6 ± 1.6 (14–20) | 18.9 ± 2.5 (14–20) |
| Stiffness | 6.1 ± 1.8 (3–8) | 6.1 ± 0.9 (4–8) |
| Physical function | 51.5 ± 3.5 (45–59) | 51.1 ± 4.5 (42–60) |
| Preoperative alignment | ||
| HKA |
173.7° ± 2.4° (169.6°–177.8°) |
172.2° ± 1.8° (169.6°–175.8°) |
| WBL% |
22.8 ± 7.8 (10.0–35.0) |
24.5 ± 6.9 (10.0–36.0) |
| MPTA |
85.3° ± 2.2° (81.7°–88.7°) |
84.4° ± 2.4° (81.6°–88.0°) |
| LDFA |
81.7° ± 2.3° (77.7°–85.7°) |
81.7° ± 2.8° (78.0°–85.5°) |
| JCLA |
5.0° ± 2.9° (0.4°–10.3°) |
4.6° ± 3.4° (0.7°–9.9°) |
HTO high tibial osteotomy, KL grade Kellgren–Lawrence grading scale, VAS visual analog scale, WOMAC Western Ontario and McMaster Universities Osteoarthritis Index, HKA Hip–knee–ankle angle, WBL weight-bearing line ratio, MPTA medial proximal tibial angle, LDFA lateral distal femoral angle, JLCA joint line convergence angle
Clinical improvement and radiographic outcomes
Compared with the preoperative values, there were significant improvements in the VAS and WOMAC scores at years 1, 3, and 5 postoperatively (Table 2). In group A, the HKA angle was 173.7° ± 2.4° (range, 169.6°–177.8°) preoperatively and was maintained at 183.8° ± 2.3° (range, 180.3°–187.9°) at the 5-year follow-up after HTO. The WBL% shifted significantly from 22.8% ± 7.9% (range, 10.0%–35.0%) preoperatively to 61.3% ± 14.8% (range, 38.0%–86.0%) postoperatively, aligning near the Fujisawa point. The MPTA increased from a mean of 85.3° ± 2.2° (range, 81.7°–88.7°) preoperatively to 89.3° ± 1.3° (range, 87.0°–91.3°) postoperatively following MOWHTO. No significant changes were observed in aLDFA between preoperative and postoperative measurements, whereas JLCA demonstrated a measurable improvement. In group B, the preoperative HKA angle was 172.3° ± 1.8° (range, 169.6°–175.8°), which improved to 185.0° ± 2.4° (range, 180.6°–187.5°) at the 5-year postoperative follow-up. The WBL% shifted from 24.5% ± 6.9% (range, 10.0%–36.0%) preoperatively to 54.2% ± 9.4% (range, 38.0%–68.0%) at 5 years postoperatively. The MPTA was maintained at 90.9° ± 1.4° (range, 89.4°–93.2°) at the 5-year follow-up. Similar to group A, no significant differences were observed in aLDFA before and after surgery, suggesting that the femoral alignment remained stable throughout the follow-up period and that the small variations observed were most likely attributable to measurement variability. Notably, in both groups, the WBL% and MPTA showed a slightly decreasing trend over the 5-year follow-up period. Detailed annual changes in radiological parameters are presented in Table 3. Figure 2 illustrates representative radiographic changes in a patient from the preoperative to the 5-year follow-up.
Table 2.
Postoperative functional outcome
| Preoperative | Post-HTO 1 year | Post-HTO 3 years | Post-HTO 5 years | |||
|---|---|---|---|---|---|---|
| Group A (N = 63) | ||||||
| VAS |
7.4 ± 0.9 (6–9) |
1.2 ± 0.9* (0–3) |
1.1 ± 1.1* (0–3) |
1.6 ± 1.1* (0–4) |
||
| WOMAC | ||||||
| Pain |
17.6 ± 1.6 (14–20) |
1.6 ± 1.1* (0–4) |
1.7 ± 1.1* (0–4) |
1.5 ± 1.1* (0–4) |
||
| Stiffness |
6.1 ± 1.8 (3–8) |
1.6 ± 1.2* (0–4) |
1.5 ± 1.1* (0–4) |
1.5 ± 1.2* (0–4) |
||
| Physical function |
51.5 ± 3.5 (45–59) |
5.6 ± 1.8* (2–9) |
5.4 ± 1.8* (2–9) |
6.2 ± 2.2* (2–11) |
||
| Group B (N = 15) | ||||||
| VAS |
7.9 ± 1.2 (6–9) |
0.9 ± 0.8* (0–3) |
1.7 ± 1.2* (0–4) |
1.5 ± 1.0* (0–4) |
||
| WOMAC | ||||||
| Pain |
18.9 ± 2.5 (14–20) |
1.1 ± 0.9* (0–3) |
1.5 ± 1.1* (0–4) |
1.9 ± 1.2* (0–4) |
||
| Stiffness |
6.1 ± 0.9 (4–8) |
1.4 ± 0.8* (0–3) |
1.1 ± 1.1* (0–3) |
1.5 ± 1.0* (0–4) |
||
| Physical function |
51.1 ± 4.5 (42–60) |
5.9 ± 2.1* (2–10) |
5.9 ± 2.4* (1–11) |
6.9 ± 1.5* (4–10) |
||
*P value < 0.001 compared with the preoperative values
HTO high tibial osteotomy, BMI body mass index, VAS visual analog scale, WOMAC Western Ontario and McMaster Universities Osteoarthritis Index
Table 3.
Radiographic evaluation of alignment following HTO
| Preoperative | Post-HTO 1 year | Post-HTO 3 years | Post-HTO 5 years | ||||
|---|---|---|---|---|---|---|---|
| Group A (N = 63) | P value | P value | P value | ||||
| HKA |
173.7 ± 2.4 (169.6°–177.8°) |
183.9 ± 2.2 (180.2°–187.7°) |
< 0.001 |
184.0 ± 2.1 (180.4°–188.0°) |
< 0.001 |
183.8 ± 2.3 (180.2°–187.9°) |
< 0.001 |
| WBL% |
22.8 ± 7.8 (10.0–35.0) |
64.6 ± 13.8 (39.0–86.0) |
< 0.001 |
65.7 ± 14.2 (39.0–86.0) |
< 0.001 |
61.3 ± 14.8 (38.0–86.0) |
< 0.001 |
| MPTA |
85.3 ± 2.2 (81.7°–88.7°) |
91.3 ± 2.0 (88.1°–95.0°) |
< 0.001 |
91.1 ± 1.9 (87.6°– 94.4°) |
< 0.001 |
89.3 ± 1.3 (87.0°–91.3°) |
< 0.001 |
| LDFA |
81.7 ± 2.3 (77.7°–85.7°) |
82.5 ± 3.6 (77.3°–88.2°) |
0.205 |
82.0 ± 3.32 (77.2°–87.7°) |
0.550 |
81.8 ± 3.2 (77.3°–87.9°) |
0.860 |
| JCLA |
5.0 ± 2.9 (0.4°–10.3°) |
3.8 ± 2.5 (0.2°–8.0°) |
0.039 |
4.1 ± 2.3 (0.2°–8.0°) |
0.042 |
3.6 ± 2.8 (0.3°–8.1°) |
0.002 |
| Group B (N = 15) | P value | P value | P value | ||||
|---|---|---|---|---|---|---|---|
| HKA |
172.2 ± 1.8 (169.6°–175.8°) |
184.2 ± 2.4 (180.2°–187.6°) |
< 0.001 |
183.9 ± 2.0 (180.1°–186.7°) |
< 0.001 |
185.0 ± 2.4 (180.6°–187.4°) |
0.001 |
| WBL% |
24.5 ± 6.9 (10.0–36.0) |
59.4 ± 29.0 (40.0–86.0) |
< 0.001 |
58.4 ± 11.9 (40.0–72.0) |
< 0.001 |
54.2 ± 9.4 (38.0–68.0) |
< 0.001 |
| MPTA |
84.4 ± 2.4 (81.6°–88.0°) |
91.4 ± 1.9 (89.6°–93.3°) |
< 0.001 |
91.3 ± 9.7 (89.7°–93.2°) |
< 0.001 |
90.9 ± 1.4 (87.1°–93.4°) |
< 0.001 |
| LDFA |
81.7 ± 2.8 (78.0°–85.5°) |
82.7 ± 2.6 (77.6°–85.4°) |
0.177 |
81.8 ± 2.2 (78.8°–85.4°) |
0.442 |
82.1 ± 2.5 (78.3°–85.3°) |
0.328 |
| JCLA |
4.6 ± 3.4 (0.7°–9.9°) |
3.5 ± 2.5 (0.6°–8.1°) |
0.352 |
4.5 ± 2.9 (0.9°–8.9°) |
0.934 |
4.2 ± 2.6 (0.7°–8.9°) |
0.737 |
BMI body mass index, HKA hip–knee–ankle angle, HTO high tibial osteotomy, WBL weight-bearing line ratio, MPTA medial proximal tibial angle, LDFA lateral distal femoral angle, JLCA joint line convergence angle
*Varus alignment is expressed as HKA values < 180°, whereas valgus alignment is expressed as values > 180°
Fig. 2.
A 70-year-old female patient with a BMI of 38 kg/m2 who underwent bilateral high tibial osteotomy. A Preoperative standing radiograph; B 1-year, C 3-year, and D 5-year postoperative radiographs showing sustained correction and excellent knee alignment
Complications and conversion to TKA
Among the 78 knees, lateral hinge fractures were observed in two knees in group A and in one knee in group B, all of which had type 1 lateral hinge fractures. These patients continued active knee motion through non-weight-bearing methods, and at the 5-year follow-up, they successfully maintained the corrected angle. No postoperative fractures, delayed union, nonunion, or infections were reported as complications. If patients experienced discomfort from locking plate irritation of the subcutaneous tissue, plate removal surgery was scheduled at least 1 year later. Over the 5-year follow-up period, a total of 36 cases (48%) underwent implant removal surgery, whereas two knees in group A and one knee in group B underwent conversion to TKA. The primary reasons for conversion were recurrent degeneration of the medial knee compartment and patellofemoral osteoarthritis, which caused anterior knee pain. These patients opted for TKA to address the overall issues. The 5-year conversion to TKA rate was 3.8%.
Discussion
The present study found that MOWHTO can provide sustained symptomatic improvement and acceptable midterm alignment control in patients with obesity when appropriate surgical planning and fixation strategies are applied. The use of 3D-printed PSI may offer potential advantages for patients with obesity undergoing high tibial osteotomy. Excessive soft-tissue thickness and limited anatomical landmarks in these individuals can make intraoperative alignment assessment and osteotomy execution more challenging. In this context, PSI may facilitate more accurate osteotomy planning and execution by providing a customized cutting guide based on patient-specific anatomy. Although their WBL% values gradually decreased over time, functional outcomes remained satisfactory at the 5-year follow-up, supporting the role of MOWHTO as a joint-preserving option in selected patients with obesity (Table 3). Furthermore, some patients with a JLCA greater than 2° may suggest the presence of an intra-articular component, this finding does not necessarily preclude the effectiveness of tibial osteotomy [32]. By shifting the mechanical axis laterally, the extra-articular realignment reduces the medial compartment load and may result in meaningful symptomatic improvements, even in the presence of intra-articular degeneration [33]. This effect may be particularly relevant in patients with obesity in whom excessive medial compartment load plays a major role in pain generation [3].
The favorable outcomes observed in this study may be associated with several technical and patient-related factors rather than being attributable to a single determinant. The use of an axially stabilizing locking plate may have contributed to the maintenance of construct stability; however, no comparative analysis with other fixation methods was performed. Second, preventing the occurrence of lateral hinge fractures is even more crucial in patients with high BMIs. A lateral hinge fracture may lead to instability at the osteotomy site, potentially resulting in implant breakage, loss of correction angle, or knee joint symptoms, such as pain and deformity [34, 35]. Intraoperatively, lateral hinge fractures occurred in only 3.8% (3/78) of cases, a rate comparable to that reported in previous studies [12, 36, 37]. Furthermore, the use of lateral supplemental lag screws may enhance structural stability, reducing the risk of implant failure and enabling patients to endure the period before the bony gap fully heals [29–31]. Patient-related factors, including a relatively younger age in our cohort, preserved cognitive function, and the ability to comply with postoperative partial weight-bearing rehabilitation, were also likely associated with satisfactory outcomes. Furthermore, improvements in knee pain following MOWHTO may facilitate increased physical activity and support weight management, which could help maintain postoperative functional outcomes over time.
Previous studies have demonstrated that obesity is a key factor accelerating the progression of osteoarthritis [5, 6]. In patients with knee varus deformity, increased medial compartment loading due to excess body weight further exacerbates the degeneration of intra-articular structures[3]. Concurrently, damage and thinning of the meniscus and cartilage contribute to the worsening of deformities, creating a vicious cycle [38]. In addition, adipose tissue releases various pro-inflammatory cytokines that influence cartilage matrix synthesis and metabolism, leading to cartilage degradation, subchondral bone proliferation, and an increased risk of knee osteoarthritis [39]. These factors collectively establish obesity as an anatomical and physiological risk factor for arthritis.
Given the dual burden of mechanical overload and systemic inflammation in individuals with obesity, the selection of an appropriate surgical intervention is becoming increasingly complex. MOWHTO is an important option for treating medial compartment knee osteoarthritis, particularly in younger active patients. Realigning the mechanical axis reduces stress on the damaged compartment, relieves symptoms, and postpones the need for TKA.
In general, individuals under 60 years of age with medial compartment knee osteoarthritis, BMI < 30 kg/m.2, no ligament instability, and no flexion contracture are considered ideal candidates for MOWHTO. For patients with normal BMI, mid- to long-term outcomes following MOWHTO are generally favorable [8, 40–42]. However, earlier studies have raised concerns about performing HTO in those with a BMI > 30 kg/m2. The reported risks include rapid loss of the correction angle, implant failure (e.g., plate or screw breakage), and poor wound healing, leading to the perception of obesity as a contraindication for HTO [8, 9].
For young patients with obesity and unicompartmental knee osteoarthritis, treatment options are challenging. The prognosis following unicompartmental knee arthroplasty is less favorable as the design and longevity of the implant appear suboptimal [43–47]. Nevertheless, directly opting for TKA in young patients with obesity is not without drawbacks, as patients are at a higher risk of surgical complications, including surgical site infections, wound issues, and the need for revision procedures [48]. In patients with obesity, the challenges encountered and the dilemmas in choosing the optimal surgical treatment have compelled surgeons to continue employing MOWHTO as a strategy to delay the timing of TKA.
In recent years, however, a growing body of research has suggested that obesity may not necessarily be a contraindication for HTO, prompting reassessment of its role in managing patients with obesity with unicompartmental knee osteoarthritis [13]. Recent advancements in surgical techniques, improved implant designs, and optimized perioperative management strategies have been reported to enhance the outcomes of patients with obesity undergoing HTO. Enhanced fixation methods and meticulous preoperative planning, including accurate correction of angle measurements, may mitigate complications associated with obesity. Early studies also indicated that the satisfaction level of patients with obesity is relatively lower than that of patients with a normal BMI; however, there were still significant improvements in functional scores from preoperative to postoperative assessments [10–12]. These findings confirm that MOWHTO still has significant clinical value in this patient group.
The limitations of this study include its retrospective design, the absence of a control group of patients without obesity, and the relatively small sample size. The BMI was determined based on the weight recorded the day before surgery. Postoperative weight fluctuations were not systematically captured, which may have influenced long-term mechanical loading of the knee. This raises questions about whether the observed benefits of HTO in overweight patients can be sustained for over 5 years. Despite these limitations, this study also has notable strengths. The study evaluated a cohort with a minimum 5-year follow-up, which provides valuable midterm outcome data in a population with obesity undergoing MOWHTO. Standardized surgical techniques, consistent postoperative evaluations, and detailed radiographic assessments strengthen the reliability of the reported findings. Further research is needed to explore the long-term outcomes of HTO in patients with higher BMI.
Conclusion
This retrospective study demonstrated satisfactory clinical and radiographic outcomes in patients with obesity (BMI > 30 kg/m²) who underwent MOWHTO over a 5-year follow-up period. These findings suggest that HTO may be a feasible joint-preserving treatment option for selected patients with obesity. Careful patient selection, considering age, activity level, and anticipated timing of potential conversion to total knee arthroplasty, remains essential when evaluating the appropriateness of this procedure.
Acknowledgements
Not applicable.
Abbreviations
- aLDFA
Anatomical lateral distal femoral angle
- AP
Anteroposterior
- BMI
Body mass index
- HKA
Hip–knee–ankle angle
- HTO
High tibial osteotomy
- ICC
Intraclass correlation coefficient
- IRB
Institutional Review Board
- JLCA
Joint line convergence angle
- KL
Kellgren–Lawrence
- MOWHTO
Medial open-wedge high tibial osteotomy
- MPTA
Medial proximal tibial angle
- PSI
Patient-specific instrumentation
- TKA
Total knee arthroplasty
- VAS
Visual analog scale
- WBL
Weight-bearing line
- WOMAC
Western Ontario and McMaster Universities Osteoarthritis Index
Authors contributions
Y.H.T. and K.H.L. helped write the manuscript and collect the data; Y.H.T., K.H.L., and C.S.Y. designed the study and helped revise the manuscript; C.W.H. and S.Y.L. analyzed the data. All the authors have proofread the final version of the manuscript.
Funding
The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.
Availability of data and materials
The datasets generated and/or analyzed during the current study are not publicly available due to patient privacy and institutional regulations but are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
All procedures involving human participants performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This study was approved by the Institutional Review Board of Taipei Veterans General Hospital (IRB number: 2025-02-005BC). We confirmed that all methods were performed in accordance with relevant guidelines and regulations.
Consent for publication
Not applicable.
Competing interests
The authors have no relevant financial or nonfinancial interests to disclose.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets generated and/or analyzed during the current study are not publicly available due to patient privacy and institutional regulations but are available from the corresponding author on reasonable request.