A Combined Posterior Stable Prosthesis and Medial Condylar Sliding Osteotomy Technique for Kashin-Beck Osteoarthritis

Summary

This study evaluates a surgical technique combining a posterior-stabilized prosthesis with medial femoral condylar sliding osteotomy for Kashin–Beck disease. The approach effectively corrects knee deformities, restores function, and offers a simpler, reliable, and cost-effective alternative to constrained or hinged prostheses.

Abstract

Kashin–Beck disease (KBD) is a chronic, endemic osteoarthropathy characterized by progressive joint degeneration and deformity, frequently involving the knee and resulting in severe valgus alignment and functional impairment. Conventional surgical management of severe valgus deformities, including the use of condylar constrained knee (CCK) or hinged knee (HK) prostheses, is often associated with increased surgical trauma, higher costs, and limited accessibility, particularly in resource-constrained settings. This study evaluates a surgical technique combining posterior-stabilized (PS) total knee arthroplasty with medial femoral condylar sliding osteotomy to address severe valgus deformities in KBD. A retrospective analysis was conducted on 10 patients (11 knees) treated between 2019 and 2023. Clinical outcomes were assessed using pain scores, functional scoring systems, range of motion measurements, and radiographic evaluation of alignment and prosthesis stability. Postoperative results demonstrated significant improvements in pain, knee function, and activity levels, along with restoration of limb alignment and stable prosthesis fixation. The osteotomy site achieved satisfactory bone healing in all cases. This combined technique provides effective deformity correction and joint stabilization while reducing the need for highly constrained implants, offering a simpler, reliable, and cost-effective alternative for managing KBD-associated knee deformities.

Introduction

Kashin-Beck disease (KBD) is a regionally distributed endemic osteoarthropathy characterized by multiple symmetric degeneration and necrosis of epiphyseal, growth plate, and articular cartilage during skeletal development, followed by secondary degenerative joint disease. This condition commonly affects multiple joints systemically, with particularly prominent involvement of the knee and ankle joints¹. In China, KBD exhibits a unique belt-like geographical distribution extending from Heilongjiang Province in the northeast to Sichuan and Tibet in the southwest. According to the latest systematic review data, there was a negative correlation between KBD prevalence and the publication year; the prevalence rate of KBD is approximately 0.06%². Although newly diagnosed cases have declined significantly in recent years, epidemiological data indicate that approximately 170,000 existing cases remain nationwide¹. For patients with advanced KBD, severe knee deformities represent the primary cause of functional disability, with complex pathological changes posing substantial challenges to clinical management.

Total knee arthroplasty (TKA) is an effective intervention for restoring joint function in patients with end-stage KBD-associated arthritis^1,3,4,5,6,7. Traditionally, cases complicated by severe deformities have often required constrained condylar knee (CCK) prostheses or hinged-knee prostheses to achieve adequate mechanical stability. However, these highly constrained prostheses are associated with increased surgical trauma, elevated prosthetic-bone interface stress, and significantly higher costs. These factors create substantial barriers to their widespread adoption and patient acceptance, particularly in KBD populations where medical resources are relatively scarce and financial capacity is limited.

To develop a more suitable therapeutic strategy that balances functional reconstruction requirements with economic feasibility for KBD patients, our research team has employed posterior-stabilized (PS) knee prostheses combined with a medial femoral condylar sliding osteotomy (MFCSO) to treat severe valgus deformities of the knee. This approach aims to use standard PS prostheses while achieving deformity correction and restoring joint stability through precise osteotomy techniques. Preliminary clinical applications have demonstrated promising outcomes, as summarized and reported here.

Protocol

This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki and was approved by the Medical Ethics Committee of Xianyang Central Hospital (Approval No. 2022-IRB-02). Written informed consent was obtained from all participants prior to their inclusion in the study.

Clinical data

This retrospective study included 10 patients (11 knees with valgus deformity) treated for valgus knee deformity related to KBD at the Department of Sports Medicine and Joint Surgery between November 2019 and December 2023. The cohort comprised 6 male and 5 female patients, with 6 left knees and 5 right knees affected. Representative cases are shown in Figure 1 and Figure 2 (e.g., a 53-year-old male patient). The mean disease duration was (26.91 ± 3.19) years (range, 15–50 years), the mean age was (60.73 ± 1.36) years (range, 53–69 years), the mean body mass index (BMI) was (18.86 ± 0.75) kg/m², and the mean follow-up duration was (32.5 ± 4.25) months.

Inclusion criteria were: (1) Diagnosis of KBD knee osteoarthritis (diagnostic criteria: WS/T 10026—2024); (2) Krackow type II valgus knee deformity³ with a tibiofemoral angle > 20°; (3) Age > 18 years; (4) Knee pain refractory to conservative management; (5) Scheduled for primary unilateral total knee arthroplasty; (6) Absence of severe cardiopulmonary dysfunction or coagulopathy.

Exclusion criteria were: (1) neuromuscular disease affecting knee function; (2) severe extra-articular deformity; (3) severe osteoporosis; (4) obesity (BMI > 30 kg/m²); (5) previous knee surgery or fracture history; (6) active systemic infection.

Surgical approach and initial exposure

The patient was positioned supine. A standard midline skin incision was made over the knee, followed by a medial parapatellar arthrotomy. The hypertrophic synovium, medial and lateral menisci, and both the anterior and posterior cruciate ligaments were excised.

Distal femoral osteotomy

The distal femoral cut was performed using intramedullary guidance. The entry point for the intramedullary rod was selected approximately 1 cm anterior to the insertion of the posterior cruciate ligament in the intercondylar notch and positioned slightly medial (2–3 mm) compared with conventional total knee arthroplasty. The valgus angle was determined based on the patient-specific femoral distal valgus angle (FDA) measured from preoperative full-length radiographs, typically ranging from 3° to 5°. In cases of severe valgus deformity (tibiofemoral angle > 25°), a 5° valgus angle was selected to facilitate lateral gap balancing. Resection thickness was initially set at 9 mm, with an additional 2–4 mm of bone removed depending on the degree of lateral condylar hypoplasia to ensure adequate lateral support following osteotomy. In cases of lateral femoral condyle defects, bone deficiencies were reconstructed using 3.5 mm cortical screws combined with cement augmentation.

Proximal tibial osteotomy

The proximal tibial cut was performed using extramedullary guidance. The osteotomy was oriented perpendicular to the tibial mechanical axis in the coronal plane, with a posterior slope of 3°. Rotational alignment of the tibial component was established using the line connecting the medial border of the patellar tendon and the midpoint of the posterior cruciate ligament as reference landmarks.

Femoral preparation

Femoral component size was determined based on the posterior condyles. Component rotation was aligned parallel to the surgical transepicondylar axis. Femoral bone cuts were completed using a four-in-one cutting block.

Lateral release

Following insertion of the spacer block, the medial and lateral gaps were assessed in full extension and at 90° of flexion. When the lateral gap was tight and the medial gap relatively loose, a sequential lateral soft tissue release was performed. Osteophytes were removed from the lateral femoral condyle and the posterolateral tibial plateau. At the joint line, a pie-crusting release of the iliotibial band was performed using an injection needle (Type: 1.2×32TWLB). If tightness persisted, the posterolateral joint capsule was released. Care was taken to protect the popliteus tendon and the common peroneal nerve. Release was continued until the lateral gap accommodated the planned thickness of the polyethylene insert.

Medial femoral condylar sliding osteotomy

This procedure was performed when the medial gap remained more than 4 mm larger than the lateral gap after lateral release.

A. Osteotomy design and execution

A sagittal plane osteotomy of the medial femoral condyle was performed using an osteotome rather than an oscillating saw. The osteotomy included the footprint of the proximal attachment of the medial collateral ligament. The osteotomy fragment thickness was maintained at approximately 8 mm (range, 5–8 mm).

B. Fragment shift and fixation

The osteotomy fragment, along with the attached medial collateral ligament, was shifted proximally and slightly anteriorly. Stability in extension and flexion was assessed using spacer blocks of equal thickness until balanced medial and lateral tension was achieved. The fragment was fixed to the femur using two to three 3.5 mm cortical screws, directed from anteroinferior to posterosuperior, while avoiding penetration into the intercondylar notch and the region potentially occupied by a femoral stem.

Patellar tracking and final implant placement

After placement of the trial components, patellar tracking was assessed using the no-thumb test. In cases of lateral patellar tilt or subluxation, a lateral retinacular release was performed until central tracking within the femoral trochlear groove was achieved. If tracking remained suboptimal, medial patellar facetectomy was considered to improve patellofemoral articulation. The goal was to achieve optimal tracking with a negative no-thumb test. Final implantation was performed using cemented, posterior-stabilized, fixed-bearing total knee prostheses from the same domestic manufacturer. Figure 3 shows some photos of the surgical procedure.

Postoperative management

Immediately after recovery from anesthesia, patients began ankle pump exercises and isometric quadriceps contractions under the guidance of physical therapists. On postoperative day 1, radiographic evaluation was performed to assess prosthesis placement. Prophylactic antibiotics were administered for 24 h, anticoagulation therapy was continued for 35 days, and an adjustable lower limb orthosis was applied for knee protection. Rehabilitation progressed as follows: non-weight-bearing knee flexion exercises were initiated on postoperative day 2; partial weight-bearing was allowed within 1 month; and full weight-bearing was achieved by 2 months. Radiographic confirmation of osteotomy healing was obtained within 3 months, after which the orthosis was discontinued.

Functional evaluation parameters

Follow-up assessments were conducted at 1, 3, 6, and 12 months postoperatively, and annually thereafter. Preoperative and final follow-up data were recorded for analysis. Outcome measures included pain assessed using the Visual Analogue Scale (VAS), function evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and range of motion measured with a standard goniometer. Knee-specific scores included the Knee Society Score (KSS) and the Hospital for Special Surgery (HSS) knee score. Activity level was assessed using the University of California, Los Angeles (UCLA) activity score. Radiographic evaluation included measurement of tibiofemoral angles on full-length standing radiographs using the institutional PACS system, and assessment of prosthesis positioning according to standard radiographic criteria.

Statistical analysis

Data were analyzed using SPSS 21.0 statistical software. Continuous data are presented as mean ± standard deviation. Paired t-tests were used to compare preoperative and postoperative parameters. A p-value of ≤ 0.05 was considered statistically significant.

Results

Comparison of knee pain scores

Preoperative scores on VAS and WOMAC were 7.55 ± 0.93 and 71.09 ± 7.13, respectively. Postoperative scores improved to 1.18 ± 0.40 and 7.09 ± 3.24, respectively. A paired t-test revealed that these improvements were statistically significant (p < 0.01; Table 1).

Knee joint functional score comparisons

Preoperative scores were as follows: KSS-clinical, 25.82 ± 12.94; KSS-functional, 19.09 ± 9.44; HSS, 33.73 ± 10.72; and UCLA, 2.82 ± 0.98. Postoperatively, these scores significantly improved to: KSS-clinical, 87.27 ± 4.67; KSS-functional, 85.45 ± 4.72; HSS, 86.73 ± 3.35; and UCLA, 6.55 ± 0.52. The improvements in all outcome measures were statistically significant (p < 0.01 for all; Table 2).

Comparison of knee imaging findings and range of motion

All patients recovered uneventfully, and no procedure-related complications occurred. Final follow-up imaging in all cases confirmed a stable, well-fixed prosthesis in position without evidence of loosening or migration. A non-progressive radiolucent line was observed at the cement-bone interface in one patient. Complete bony union of the medial femoral condyle sliding osteotomy was confirmed radiographically.

Statistically significant differences were observed between preoperative and postoperative measurements of the tibiofemoral angle, knee flexion, and knee extension (Table 3).

Data Availability:

All raw data supporting the findings of this study have been made publicly available as Supplementary Files accompanying this article.

Figure 1: A 53-year-old male patient with a 20-year history of bilateral knee pain (diagnosis: Kashin-Beck disease knee osteoarthritis). (A) Preoperative clinical photograph. (B,C) Preoperative anteroposterior and lateral radiographs of the knee. Imaging reveals lower limb alignment consistent with valgus knee deformity, hypoplasia of the lateral femoral condyle, and erosion with deficiency of the lateral tibial plateau. (D) Preoperative full-length standing radiographs of both lower limbs. (E) Preoperative anteroposterior radiograph of the right hand. (F) Preoperative anteroposterior radiograph of the left hand. Please click here to view a larger version of this figure.

Figure 2: Radiographic assessment at final follow-up (17 months postoperatively). (A) Full-length standing, (B) anteroposterior, and (C) lateral radiographs demonstrate restored lower limb alignment, stable knee prosthesis positioning, a symmetrical mediolateral joint space, and complete bony union of the osteotomized fragment at the medial femoral condyle. Please click here to view a larger version of this figure.

Figure 3: Intraoperative Steps of Medial Femoral Condylar Sliding Osteotomy and PS Prosthesis Implantation. (A) Intraoperative view shows that the femoral condyle of the KBD patient is flatter, with its mediolateral (ML) diameter significantly larger than its anteroposterior (AP) diameter. (B) After osteotomy, the medial joint space is noticeably larger than the lateral space (black arrow). (C) The prepared sliding bone block from the medial femoral condyle (black arrow). (D) After adjusting the sliding bone block to maintain balance in the knee flexion and extension gaps, it is fixed using a 3.5-mm cortical bone screw (black arrow). (E) The sliding bone block is displaced proximally and fixed (black arrow). (F) Post-implantation view of the PS prosthesis, demonstrating balanced flexion gap. Please click here to view a larger version of this figure.

Outcome measure	Preoperative	Postoperative	P value
VAS score	7.55±0.93	1.18±0.40	<0.01
WOMAC score	71.09±7.13	7.09±3.24	<0.01

Table 1: Comparison of preoperative versus postoperative pain scores.

Functional scores	Preoperative	Postoperative	P value
KSS clinical score	25.82 ± 12.94	87.27 ± 4.67	<0.01
KSS functional score	19.09 ± 9.44	85.45 ± 4.72	<0.01
HSS score	33.73 ± 10.72	86.73 ± 3.35	<0.01
UCLA activity score	2.82 ± 0.98	6.55 ± 0.52	<0.01

Table 2: Comparison of knee joint functional scores before and after surgery in patients.

Imaging and ROM	Preoperative	Postoperative	P value
Tibiofemoral angle	27.36±9.14	5.00±2.41	<0.01
Extension angle	-12.18±5.58	-2.27±3.44	<0.01
Flexion angle	84.55±10.83	109.55±7.57	<0.01

Table 3: Comparison of tibiofemoral angle and knee range of motion before and after surgery (mean ± SD).

Supplementary File: Individual patient-level clinical and radiographic data. This file contains the raw dataset for all included patients, including demographic characteristics, preoperative and postoperative clinical scores, range of motion, radiographic parameters, and follow-up data used for statistical analysis in this study.Please click here to download this file.

Discussion

The primary objectives of TKA are to restore lower-limb mechanical alignment and achieve balanced medial-lateral soft-tissue tension. However, achieving these goals is particularly challenging in patients with Krackow type II valgus deformities exceeding 20°. Excessive soft tissue release can lead to postoperative instability, necessitating constrained or hinged prostheses, which are associated with increased wear rates, shorter longevity, and compromised proprioception. Pang et al.⁸ showed that constrained prostheses induce more pronounced joint line alterations than nonconstrained alternatives. In severe valgus deformities, conventional soft tissue release often fails to achieve balanced joint reconstruction.

To address this, we propose a novel strategy for severe (>20°) Krackow type II valgus deformities, especially in KBD: a standard posterior-stabilized (PS) prosthesis combined with a proximal medial femoral condylar sliding osteotomy (MFCSO). This technique adjusts medial collateral ligament tension via bone repositioning rather than extensive lateral release, aiming to achieve balanced gaps and constitutional alignment while avoiding constrained implants and their associated risks^{9,10,11,12,13}.

Lateral soft tissue release and its limitations

Lateral release remains fundamental for valgus knees, starting with osteophyte removal. It involves the posterolateral capsule, popliteus tendon, lateral collateral ligament (LCL), and iliotibial band (ITB). However, when complete release fails to balance the knee, Williot A et al.¹⁴ have used constrained prostheses, which carry higher long-term loosening and instability rates. Easley et al.¹⁵ reported unacceptable late instability after transverse ITB division combined with LCL and popliteus tendon detachment. Li et al.¹⁶ found increased dislocation risk with constrained condylar prostheses after releasing these structures. Moreover, constrained prostheses are often unaffordable for impoverished KBD populations. Excessive lateral release also enlarges the bony resection space, necessitating thicker polyethylene inserts, elevating the joint line, and increasing patellofemoral pressure. Overzealous release risks common peroneal nerve injury; lengthening should generally not exceed 1 cm.

Our approach to soft tissue balancing

We use a PS prosthesis and excise the posterior cruciate ligament while preserving the popliteus tendon and LCL to avoid severe instability. ITB release is typically limited to pie-crusting or subperiosteal release rather than complete transection. The release principle is to palpate high-tension areas under distraction and release accordingly, with caution to avoid the common peroneal nerve.

Given that valgus deformity involves both lateral tightness and medial laxity, some authors advocate tightening the medial side. Li et al.¹⁷ used MCL advancement for deformities >20°, avoiding constrained implants. Healy et al.¹⁸ described MCL reattachment via a bone plug. Engh et al.¹² first described femoral condylar sliding osteotomy, and Eachempati et al.¹³ classified it into proximal medial or distal lateral types. In KBD, we use proximal MFCSO to tighten lax medial tissues, accommodating tight lateral structures, reducing lateral release, and preventing excessive gap widening and patellofemoral pressure elevation. Intraoperatively, we observed that KBD femoral condyles are flatter than in osteoarthritis (OA), with a larger mediolateral/anteroposterior (ML/AP) ratio, consistent with Yang et al.¹⁹. Thus, an AP‑sized femoral component may under‑cover the ML dimension in KBD but overhang in OA. Current prostheses are not designed for KBD morphology. The flatter condyles in KBD provide better space and fixation for sliding osteotomy, making these patients more suitable candidates. In valgus knees with lateral patellar subluxation, positioning the femoral component slightly laterally optimizes tracking and accommodates the medial osteotomy.

Selecting the appropriate valgus osteotomy angle of the femur

The optimal femoral valgus correction angle in valgus knee arthroplasty remains controversial. Rossi et al.²⁰ suggested that a 3° valgus cut effectively corrects lower limb alignment. Typically, the volume of bone resected from the medial femoral condyle significantly exceeds that from the lateral condyle, sometimes even necessitating bone grafting on the lateral side. Although satisfactory limb alignment can be achieved, this approach may result in a relatively lax medial extension gap and a tight lateral gap, complicating soft tissue balancing. Excessive lateral soft tissue release can cause knee instability, potentially necessitating the use of constrained prostheses. Shuai-Jie Lv et al.²¹ employed a 5°–7° femoral valgus cut for severe valgus knees, accepting a residual 2° inaccuracy in the tibiofemoral angle. This strategy reduced the need for extensive soft-tissue release, maintained early joint stability, decreased the need for constrained implants, and lowered postoperative complication rates. Tucker et al.²² recommended using a 5° or greater valgus cut if an imbalance exists in the extension gap. Conversely, Shi X et al.²³ and Rahm et al.²⁴ advocated for patient-specific valgus angles determined from the femoral anatomical and mechanical axes.

However, achieving a truly precise valgus angle is challenging in valgus knees. Lateral femoral condylar hypoplasia can cause a shift in the knee centerline, while the frequent presence of femoral internal rotation deformity complicates the accurate identification of the true anatomical axis. Selecting a smaller valgus angle can adequately correct limb alignment but risks under-resection of the lateral femoral condyle, potentially compromising lateral support. A larger valgus angle eases soft-tissue balancing pressures but sacrifices limb alignment, potentially leaving a residual valgus deformity.

Our approach uses a 3°–5° distal femoral valgus cut, which effectively corrects lower limb alignment. Mediolateral gap balance is achieved through appropriate soft tissue releases combined with a medial femoral condylar sliding osteotomy. This technique allows the lax medial soft tissues to better accommodate the tension of the tight lateral structures. By minimizing the need for extensive lateral soft tissue release, this method facilitates effective correction of the valgus deformity and yields favorable functional outcomes.

Correcting the lower limb alignment

Accurate lower limb alignment is a crucial factor in preventing postoperative prosthesis loosening. Current clinical studies have yielded conflicting findings regarding the correlation between lower limb alignment and implant survival^{25,26,27,28,29}. Neutral mechanical axis alignment or 5° to 7° valgus anatomical axis alignment remains the goal of most surgeons²⁸. In a follow-up of 115 TKAs for 8–12 years, Jeffery RS et al.²⁹ found a prosthesis loosening rate of 3% when limb alignment was within ±3° of neutral, compared to 24% when alignment deviated by more than 3°. However, Parratte et al.²⁵ reported no difference in 15-year survival rates between 292 TKAs with a postoperative mechanical axis of 0°±3° and 106 TKAs outside this range. They concluded that targeting a mechanical axis of 0°±3° has limited utility for predicting the longevity of knee replacement prostheses. Based on a study of 6070 TKAs with excellent survival rates at an average follow-up of 6.6 years, Fang et al.²⁶ recommended a target anatomical axis alignment of 2.4° to 7.2° valgus. Results showed that the preoperative tibiofemoral angle was corrected from 27° ± 9° to 5° ± 2°, accompanied by good restoration of mediolateral stability. This demonstrates that medial femoral condylar sliding osteotomy is an effective technique for treating severe valgus deformities.

Pearls and pitfalls

In summary, key technical insights from using the proximal medial femoral condylar sliding osteotomy technique for treating KBD with genu valgum are as follows: First, for type II valgus knees, the osteotomy should be guided by the lateral gap. The gap created after osteotomy should be slightly smaller than the thickness of the planned polyethylene insert. Subsequent appropriate lateral soft-tissue release will restore the normal gap width, thereby determining the appropriate amount of bone resection. Furthermore, distal femoral resection should be conservative, as excessive bone removal can compromise the medial sliding osteotomy and elevate the joint line. Second, an osteotome is preferred over an oscillating saw to perform the medial femoral condylar osteotomy, as it better preserves bone stock; an oscillating saw typically removes at least 2 mm of bone. The optimal thickness of the osteotomized bone fragment is generally 5–8 mm. An overly thick fragment may cause partial defects and reduced strength in the medial femoral condyle, compromising prosthetic positioning, while an overly thin fragment may weaken fixation strength and impair healing. Third, tension in the lax medial soft tissues is achieved by proximal advancement of the medial femoral condylar fragment. Simultaneous anterior sliding helps maintain flexion gap balance and prevents excessive medial laxity. Fourth, the repositioned fragment is typically fixed with 2–3 screws. Special attention should be paid to the screw direction to avoid penetration into the femoral intercondylar region. Fifth, for postoperative rehabilitation, exercises should be performed using an adjustable knee brace for protection. Generally, brace protection is required for 3 months postoperatively to prevent lateral stress that could lead to displacement or failure of fixation. Early partial weight-bearing ambulation with crutches is permitted, progressing to full weight-bearing only after confirmed radiographic union of the osteotomy site.

Potential risks

This technique carries specific risks: (1) Severe osteoporosis should be considered a relative contraindication, as the osteotomized bone block may fracture or the medial femoral condyle may collapse in such patients. This can lead to insufficient fixation strength to withstand the stress during knee flexion and extension, thereby significantly increasing the risk of surgical failure. A constrained knee prosthesis should be prepared preoperatively. (2) The fixation of the osteotomized fragment may be biomechanically weak. Therefore, an adjustable knee brace must be worn during early postoperative rehabilitation to prevent displacement of the fragment and nonunion at the osteotomy site caused by lateral stress. (3) Femoral component lateralization may impair patellofemoral tracking. During intraoperative assessment, if needed, patellar resurfacing or reaming can be performed to optimize tracking. (4) In patients with small femoral condyles, osteotomy increases the risk of iatrogenic condylar fracture. This risk must be carefully assessed during preoperative planning. (5) Proximal migration of the MCL insertion may alter knee kinematics; long-term outcomes require further follow-up.

Study limitations

Our study has several limitations that should be acknowledged. First, the sample size is small, which limits the generalizability of our findings. Second, this is a retrospective study, inherently subject to selection bias and incomplete data control. Third, the absence of a control group (e.g., patients treated with constrained prostheses or extensive lateral release alone) prevents direct comparative assessment of the MFCSO technique’s relative efficacy. Fourth, the mean follow-up period is relatively short, and longer-term outcomes such as implant survivorship and osteotomy fragment union beyond 5–10 years remain unknown. Despite these limitations, our study has notable strengths: it is the first to apply MFCSO in valgus knee arthritis secondary to KBD, with all operations performed by a single surgeon using a consistent technique, and we concurrently evaluated clinical and radiographic outcomes.

Future directions

Based on these preliminary findings, future research should pursue: (1) Multicenter, large‑sample, long‑term (≥10 years) studies comparing MFCSO with constrained prostheses. (2) Integration with computer navigation or patient‑specific guides to improve precision, and exploration of this technique for other etiologies (post‑traumatic, congenital). (3) Biomechanical and advanced imaging studies to quantify soft tissue tension, prosthesis‑bone interface stress, and patellofemoral tracking. (4) Ongoing follow‑up to track long‑term survival rates based on this well‑documented technique. (5)Future validation of the MFCSO technique should include prospective randomized controlled trials against constrained prostheses and cadaveric biomechanical studies comparing it with extensive lateral release to assess gap balance, ligament stress, and joint kinematics.

Contribution to the field

This study provides a validated, bone‑preserving solution for balancing severe valgus knees without constrained prostheses, expanding the surgical repertoire beyond the traditional dichotomy of extensive release versus high constraint^9,12,13. It offers critical insights for managing KBD patients through anatomical observations (flatter condyles, higher ML/AP ratio) and technical adaptation of MFCSO for this morphology¹⁹. Furthermore, the technique is cost‑effective and reproducible, advancing equitable surgical care in resource‑limited settings where expensive constrained implants are prohibitive but the burden of severe deformity is high.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Knee Prosthesis – Femoral Condyle	Beijing Lidakang Technology Co., Ltd.	50120P	Model: RY A201; Material: CoCr
Knee Prosthesis – Tibial Tray	Beijing Lidakang Technology Co., Ltd.	50130	Model: RY B401; Material: CoCr + Ti
Knee Prosthesis – Tibial Insert	Beijing Lidakang Technology Co., Ltd.	50140P-9	Model: RY C401; Material: PE
Bone Cement (PALACOS R+G)	Heraeus Medical GmbH	LOT 76171594	Material: Polymethyl methacrylate (PMMA)
Metal Bone Screw (Cortical)	Tianjin Zhengtian Medical Equipment Co., Ltd.	T500035028	Model: HA004; Material: T (Material Code)
Disposable Sterile Injection Needle (C)	Zhejiang Kangkang Medical Devices Co., Ltd.	230715	Model: 1.2×32TWLB; Material: Not stated
SPSS 21.0 statistical software	IBM Corp	Version 21.0	Used for statistical analysis