# Biomechanical studies in distal femoral osteotomy: A literature review

Sohrab Rezaei, Massamaesso Bilasse, Yamen Othmani, Nadia Bahlouli, Matthieu Ehlinger

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Sohrab Rezaei, Massamaesso Bilasse, Yamen Othmani, Nadia Bahlouli, Matthieu Ehlinger. Biomechanical studies in distal femoral osteotomy: A literature review. Next Research, 2025, 4, pp.101207. 10.1016/j.nexres.2025.101207. hal-05459756

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# Biomechanical studies in distal femoral osteotomy: A literature review

Sohrab Rezaei<sup>a,b,*</sup> <sup>Δ</sup>, Massamaesso Bilasse<sup>a,b</sup>, Yamen Othmani<sup>a,b</sup>, Nadia Bahlouli<sup>a</sup>, Matthieu Ehlinger<sup>a,c</sup>

## ARTICLE INFO

### Keywords:

Valgus knee

Distal femoral osteotomy

Biomechanics

Hinge fracture

Osteotomy fixation

Correction stability

## ABSTRACT

**Background:** Distal femoral osteotomy (DFO) is a surgical intervention primarily indicated for the correction of valgus malalignment of the knee associated with lateral compartment osteoarthritis. Despite its increasing use, the biomechanical principles underlying this procedure remain insufficiently synthesized.

**Objectives:** This review aims to synthesize experimental, numerical and observational studies investigating the biomechanics of DFO, identify key determinants of surgery outcomes and highlight current limitations and future research directions.

**Method:** A systematic search of PubMed and Web of Science databases was conducted for studies published between 2010 and 2025 using combined keywords related to femoral osteotomy. Eligible studies included original works providing direct biomechanical data or analyses of DFO.

**Results:** Forty-five studies met the inclusion criteria, including 30 primary research articles with direct biomechanical investigations and 15 additional observational studies presenting relevant biomechanical implications. Overall, these studies revolved around the following topics: hinge fracture, correction stability and correction outcome.

**Conclusions:** Hinge position was the primary factor influencing fracture risk, with condylar hinge placement reducing fracture incidence. Bi-planar cuts improved cortical contact and promoted faster bone healing. Angled blade plates provided the highest stiffness, while locking plates achieved comparable stability when supported by hinge screws or grafts. Future research should focus on defining the optimal correction angle, developing hinge fracture models, assessing the biomechanics of postoperative recovery and evaluating the influence of gap fillers.

## 1. Introduction

Distal femoral osteotomy (DFO) is a surgical intervention primarily indicated for the correction of valgus malalignment of the knee associated with lateral compartment osteoarthritis for a metaphyseal deformation of the distal femur. This procedure is particularly recommended for young and active individuals experiencing isolated lateral compartment arthritis [1]. The operation, though technically demanding, shows promising early survivorship and significant improvements in patient-reported outcome scores [2].

The mechanical axis of the lower limb is determined by drawing a line from the centre of the femoral head to the centre of the ankle (Fig. 1a). Under normal circumstances, this axis passes through the centre of the knee [3]. In individuals with valgus malalignment, however, the mechanical axis deviates laterally, shifting the ground reaction

force vector toward the lateral compartment. This altered alignment results in abnormal joint contact areas and elevated contact pressures within the lateral tibiofemoral compartment, accelerating cartilage degeneration and structural deterioration [3]. From a biomechanical standpoint, DFO seeks not only to realign the mechanical axis, typically towards a neutral or slightly valgus position (1°), but also to restore more balanced load distribution across the joint surfaces during gait and weight-bearing. The optimal degree of correction, however, remains a topic of ongoing debate.

In cases of significant lateral compartment degeneration or valgus knee deformity, distal femoral osteotomy (DFO) serves as a joint-preserving alternative to arthroplasty, potentially delaying the need for total knee replacement. The surgical approach, whether it be a medial closing wedge (MCW-DFO) or lateral opening wedge (LOW-DFO), is selected based on the required correction angle, the patient's

<footnote><sup>a</sup> ICube – Laboratoire des sciences de l'ingénieur, de l'informatique et de l'imagerie, UMR 7357, Université de Strasbourg, CNRS, Strasbourg 67000, France</footnote>

<footnote><sup>b</sup> ICAM site de Strasbourg-Europe, 2 rue de Madrid, Schiltigheim 67300, France</footnote>

<footnote><sup>c</sup> Service de chirurgie orthopédique et de traumatologie, Hopital de Hautepierre, Hôpitaux universitaires de Strasbourg, 1 avenue Molière, Strasbourg 67098, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: srezaeilafmejani@unistra.fr (S. Rezaei).</footnote>
<figure><img src="image_2.png" /><figcaption>**Fig. 1.** Representation of DFO procedure: (a) unhealthy mechanical axis (b) correction by open-wedge DFO (c) correction by closed-wedge DFO.</figcaption></figure>

overall health status, bone quality, limb length and level of physical activity [4]. Preoperative planning is critical to ensure appropriate mechanical axis realignment and optimize post-operative outcomes [5].

During DFO (Fig. 1), an osteotomy is performed on either the medial or lateral side of the distal femur, depending on the correction strategy. Various cut orientations and configurations exist [6], including perpendicular or oblique single-plane cuts, which are technically simpler but may disrupt soft tissue and bi-plane cuts that preserve anterior gliding structures and increase cortical contact. In MCW-DFO, a medial wedge of bone is resected and the gap is closed, while in LOW-DFO, a lateral cut is opened around an intact “medial hinge” [7], allowing correction by opening the cut. Bone grafts may be inserted in the created gap based on the correction angle. Finally, the correction in both techniques is stabilized with plates and screws. The goal in each case is to redistribute joint loading from the affected lateral compartment to the healthier medial side [4].

Postoperatively, patients typically experience substantial pain relief and improved knee function, primarily due to restored limb alignment. Studies demonstrate high early survivorship and marked improvements in patient-reported outcomes following DFO [8]. These benefits are largely attributed to the redistribution of joint loads and reduction of abnormal stress on the degenerated compartment [1]. In addition to bony correction, DFO alters tension in surrounding soft tissues such as the medial collateral ligament (in LOW-DFO) or lateral structures (in MCW-DFO), which can influence joint stability and post-operative load sharing.

Recovery involves a structured rehabilitation protocol beginning with immobilization, followed by progressive weight-bearing as tolerated. Most patients resume daily activities within 3 to 6 months postoperatively, while returning to high-impact activities may require a longer recovery period, depending on individual factors [9]. Notably, the biomechanical consequences of these rehabilitation protocols on bone healing and functional restoration remain largely unexamined.

While several reviews have addressed the biomechanical aspects of high tibial osteotomy (HTO) [10,11], no comprehensive synthesis of biomechanical studies focused specifically on DFO is currently available. Although DFO and HTO share similarities in surgical approach and osteotomy technique, key differences in anatomical geometry, morphological characteristics and load-bearing conditions limit the direct applicability of HTO findings to DFO. Therefore, a dedicated review of the biomechanics of DFO would be valuable for clarifying current knowledge and guiding future research.

The aim of this review is to synthesize recent advances in the

biomechanics of DFO, with a particular emphasis on experimental and numerical modelling studies. Additionally, the review seeks to identify existing limitations and knowledge gaps in the current literature, thereby outlining directions for future research.

## 2. Methods

### 2.1. Search strategy

A systematic study of the literature was carried out across the databases of PubMed and Web of Science on 20 January 2025 and updated on 23 October 2025. The search was conducted using the Boolean operator AND/OR with the following keywords on the titles: (“osteotomy” OR “osteotomies”) AND (“femur” OR “femoral” OR “lower extremity” “knee” OR “condylar” OR “supracondylar” OR “varus” OR “valgus” OR “varisation” OR “valgisation” OR “varization” OR “valgization”). The timeframe of publications was limited to studies over the period of 2010–2025.

### 2.2. Eligibility criteria

Studies were included if they met the following criteria: (1) being original research articles; (2) focused primarily on distal femoral osteotomy (DFO); and (3) providing direct biomechanical data or analyses relevant to DFO. Studies were excluded if they (1) were conference abstracts, posters, or single-case reports; (2) were published in languages other than English; (3) focused solely on the development of surgical instruments or techniques without biomechanical evaluation; (4) addressed DFO performed for traumatic indications; or (5) involved animal models without translational implications for human biomechanics.

### 2.3. Quality assessment

A critical appraisal of study methodologies, limitations and overall quality of evidence was performed using a modified Kmet scoring system [12]. The studies included were first categorized as experimental, numerical, or observational. A checklist of 13 criteria (Table 1) was then

<table><caption>**Table 1**

Kmet scoring items for numerical, experimental, observational studies.</caption><thead><tr><th>Criteria</th><th>Finite element studies</th><th>Experimental studies</th><th>Retrospective studies</th></tr></thead><tbody><tr><td>1</td><td colspan="3">Research question clearly stated</td></tr><tr><td>2</td><td colspan="3">Study design appropriate to answer question</td></tr><tr><td>3</td><td>Method of model generation clearly described</td><td>Sample preparation well described</td><td>Source of data clearly described</td></tr><tr><td>4</td><td>Material properties justified and realistic</td><td>Material properties or characteristics of samples</td><td>Inclusion/exclusion criteria clearly defined</td></tr><tr><td>5</td><td>Boundary conditions and loading clearly defined</td><td></td><td>Outcomes measured appropriately and objectively</td></tr><tr><td>6</td><td>Mesh convergence analysis or sensitivity study done</td><td>Experimental setup and instruments justified</td><td>Confounding variables addressed</td></tr><tr><td>7</td><td>Contact/interface definitions and interactions described</td><td>Sample size appropriate and justified</td><td></td></tr><tr><td>8</td><td>Validation of model with experimental or literature data</td><td>Consistency/ repeatability of procedure</td><td>Transparency and Replicability</td></tr><tr><td>9</td><td>Outcome measures are clearly defined and justified</td><td>Data acquisition and analysis methods appropriate</td><td>Validity of outcome measures</td></tr><tr><td>10</td><td colspan="3">Statistical analysis correct (if applicable)</td></tr><tr><td>11</td><td colspan="3">Results are reported in sufficient detail</td></tr><tr><td>12</td><td colspan="3">Conclusions supported by the results</td></tr><tr><td>13</td><td colspan="3">Limitations of the model/study are stated</td></tr></tbody></table>
applied, tailored to each study type. Each criterion was scored as 2 = yes, 1 = partial, or 0 = no. The overall Kmet quality score was calculated by dividing the total score by the maximum possible score and expressed as a percentage. Scores of (≤ 50%, 50-66.9%, 67-84% and ≥ 84% were interpreted as indicating poor, fair, good and excellent methodological quality, respectively [12].

# 3. Results and discussion

## 3.1. Literature search

A total of 4045 studies were initially identified across the databases. After removing duplicates, 2294 studies remained for title and abstract screening. Of these, the full texts of 76 studies were reviewed in detail, resulting in the inclusion of 30 primary research articles with direct biomechanical investigations and 15 additional observational studies presenting relevant biomechanical implications. Fig. 2 summarizes the process and results of the literature search.

The average Kmet score of the studies included was 86 % with 27 studies of excellent quality, 17 studies of good quality and one study of fair quality.

Ultimately, 45 articles were selected for their contribution to the biomechanical study of DFO, as summarized in Table 2. Generally, these studies revolve around the following topics: hinge fracture, correction stability and correction outcome. In the following, each of these topics is therefore investigated and findings are given and discussed.

## 3.2. Hinge fracture

Lateral and medial cortical hinge fractures have been reported in approximately 48 % of cases following MCW and 39 % following LOW procedures [13,14]. Such fractures can substantially compromise post-operative stability and overall outcomes of DFO, leading to complications, delayed bone healing, or loss of correction, particularly in LOW configurations [15]. A detailed understanding of the biomechanical determinants of hinge failure and the measures that can mitigate these risks is therefore essential to refine surgical planning and improve patient recovery.

### 3.2.1. Fracture classification

In a radiographic analysis of 100 LOW-DFOs, Winkler et al. [16] classified medial cortical hinge fractures into three distinct types according to the direction of propagation relative to the osteotomy hinge. Type 1 (the most frequent form with a rate of incidence of 76 %) represented a simple extension of the osteotomy plane through the medial cortex. Type 2 fractures (4 %) coursed distally beneath the hinge toward the metaphyseal flare, while Type 3 fractures (20 %) extended proximally above the hinge into the supracondylar region. This three-type classification mirrors the Takeuchi system [17] originally proposed for HTO and captures the dominant morphology of hinge disruptions

observed in the distal femur. These studies indicate that fractures tend to follow predictable lines of cortical weakness determined by hinge position and bone geometry.

### 3.2.2. Influence of hinge characteristics on risk of fracture

#### Condylar vs supracondylar hinge positions

Cadaveric investigations have provided clear experimental evidence that hinge position markedly affects the likelihood of lateral cortical fracture during distal femoral osteotomy. In a uni-planar MCW-DFO model, Nha et al. [18] found a fracture rate of 80 % when the hinge was placed in the supracondylar region compared with 20 % when located within the lateral condyle. The authors attributed this difference to the greater plastic deformation capacity of metaphyseal bone and the preservation of a posterior cortical bridge in the condylar configuration. Extending these findings, Fujita et al. [19] demonstrated that fractures were most frequent when the osteotomy was performed too proximally within the thick supracondylar cortex and proposed the endpoint of the distal lateral cortex (where the bone becomes thinner and more pliable) as the optimal hinge position. This region, corresponding to the inferior aspect of the lateral femoral condyle, was shown to better accommodate controlled plastic deformation and thereby reduce hinge disruption. Supporting this anatomical rationale, Kim et al. [20] quantified local bone density and soft-tissue coverage, showing that the condylar zone offers both denser cancellous support and a thicker periosteal envelope, which may further explain its reduced susceptibility to cortical fracture.

Clinical and imaging studies have reinforced these experimental findings. Nha et al. [21] reported in a cohort of 67 knees that a hinge positioned in the supracondylar area increased the odds of hinge fracture by almost ten times compared with a condylar position. In a similar context, Winkler et al. [16] showed that locating the hinge distal to the adductor tubercle substantially reduced fracture risk in LOW-DFO. More recently, Teo et al. [22] described a hinge placed at the level of the inferior metaphyseal flare and observed a fracture incidence of only 7.7 %, the lowest among comparable clinical series.

#### Hinge width

The influence of hinge width on fracture risk has been studied through the complementary works of Meisterhans et al. [23,24]. In their finite element analysis of LOW- and MCW-DFOs, increasing hinge width produced higher cortical strain, especially in MCW configurations, where values exceeded the fracture threshold. Narrow hinges (<7.5 mm) promoted controlled elastic bending, whereas wider ones (>10 mm) caused abrupt tensile failure. In contrast, biomechanical testing on porcine femora only partially confirmed these results. For LOW osteotomies, fracture risk rose with hinge width, validating the finite element prediction that smaller hinges are safer. However, in MCW, a moderate increase in hinge width enabled larger angular corrections before fracture, reflecting the greater compressive tolerance of this configuration.

Observational studies largely corroborate the experimental findings of Meisterhans et al. [24]. In medial closing-wedge DFO, Kim et al. [25] reported that a greater length of remaining bone between the osteotomy end and the opposite cortex was associated with a higher incidence of lateral cortical hinge fracture, suggesting that an excessively wide residual bridge restricts controlled deformation and promotes abrupt cortical failure. Similarly, in lateral closing-wedge DFO, Rupp et al. [26] found that an enlarged medial cortical bridge was linked to a higher rate of hinge fracture, reinforcing the same mechanism in a closing-wedge configuration. Conversely, in lateral open-wedge DFO, Winkler et al. [16] observed fewer medial hinge fractures when the distance from the hinge to the opposite cortex (the effective hinge width) was greater, indicating that in tensile, open-wedge conditions, a moderately wider hinge may dissipate stress more effectively and reduce the likelihood of cortical disruption.

### 3.2.3. Influence of DFO technique on risk of fracture

#### LOW vs MCW

Beyond the influence of hinge width, the findings of Meisterhans

<figure><img src="image_3.png" /><figcaption>Fig. 2. Flow chart illustrating the study selection process.</figcaption></figure>
<table><caption>**Table 2**
Summary of included biomechanical studies.</caption><thead><tr><th>Study (A to Z)</th><th>Type</th><th>Focus</th><th>DFO technique</th><th>Fixation</th><th>Main finding</th><th>Kmet score</th></tr></thead><tbody><tr><td>Baris et al. [37]</td><td>Finite element</td><td>Risk of hinge fracture</td><td>Uni-planar LOW-DFO</td><td>N/A</td><td>Optimal diameter of protective wire for hinge fracture prevention</td><td>76.9 %</td></tr><tr><td>Batista et al. [30]</td><td>Experimental (composite femur)</td><td>Axial and torsional stability</td><td>Uni-planar LOW-DFO</td><td>Locking plate Angle blade plate Hinge fixator screw</td><td>Superiority of angle blade plates over locking plates in axial and torsional stability</td><td>80.8 %</td></tr><tr><td>Brinkman et al. [47]</td><td>Experimental (composite femur)</td><td>Axial and torsional stability</td><td>Uni-planar LOW- and MCW-DFOs</td><td>Locking plate Angle blade plate Spacer plate</td><td>Highest stability with oblique MCW fixed by angled blade plate</td><td>84.6 %</td></tr><tr><td>Brinkman et al. [43]</td><td>Experimental (composite femur)</td><td>Axial and torsional stability</td><td>Uni- and bi-planar MCW-DFOs</td><td>Locking plate</td><td>Higher axial and rotational stability with bi-planar cut</td><td>84.6 %</td></tr><tr><td>Dastgerdi et al. [38]</td><td>Finite element</td><td>Risk of hinge fracture</td><td>Uni-planar MCW-DFO</td><td>N/A</td><td>Optimal insertion angle of protective wire for hinge fracture prevention</td><td>84.6 %</td></tr><tr><td>Fujita et al. [19]</td><td>Observational (follow-up)</td><td>Incidence of hinge fracture and course of bone healing</td><td>Bi-planar MCW-DFO</td><td>Locking plate</td><td>Delayed bone healing and loss of correction due to hinge fracture</td><td>65.4 %</td></tr><tr><td>Hamasaki et al. [57]</td><td>Observational (retrospective)</td><td>Knee joint pressure</td><td>Bi-planar MCW-DFO</td><td>Locking plate</td><td>Reduction in lateral compartment stress after DFO</td><td>84.6 %</td></tr><tr><td>Hetsroni et al. [63]</td><td>Experimental (cadaveric)</td><td>Gait analysis</td><td>LOW-DFO</td><td>Locking plate</td><td>Improvement of knee stability by LOW-DFO in case of ligament deficiencies</td><td>92.3 %</td></tr><tr><td>Higa et al. [42]</td><td>Finite element</td><td>Risk of hinge fracture</td><td>Bi-planar MCW-DFO</td><td>N/A</td><td>Reduction of risk of hinge fracture by adding screw fixation inside hinge</td><td>75.0 %</td></tr><tr><td>Inacio et al. [70]</td><td>Finite element</td><td>Stability</td><td>N/A</td><td>N/A</td><td>Significant influence of boundary condition on evaluation of stability</td><td>88.5 %</td></tr><tr><td>Karkosch et al. [50]</td><td>Experimental (composite femur)</td><td>Axial and torsional stability</td><td>Uni-planar LOW-DFO Uni-planar MOW-DFO</td><td>Locking plate</td><td>Comparable axial and torsional stability of MOW to LOW</td><td>80.8 %</td></tr><tr><td>Kim et al. [20]</td><td>Experimental (Cadaveric)</td><td>Optimal location of hinge</td><td>Bi-planar MCW-DFO</td><td>N/A</td><td>Upper border of lateral femoral condyle recommended as ideal hinge position</td><td>92.3 %</td></tr><tr><td>Kim et al. [25]</td><td>Experimental (retrospective)</td><td>Hinge fracture</td><td>Uni-planar MCW-DFO</td><td>Locking plate</td><td>Increase in risk of hinge fracture in larger hinge width</td><td>69.2 %</td></tr><tr><td>Konrads et al. [61]</td><td>Experimental (retrospective)</td><td>Ankle and hindfoot alignment</td><td>LOW and MCW-DFO</td><td>Locking plate</td><td>Alteration of ankle orientation after DFO</td><td>80.8 %</td></tr><tr><td>Krause et al. [67]</td><td>Experimental (Cadaveric)</td><td>Ankle joint pressure</td><td>Uni-planar LOW- and MOW-DFOs</td><td>Locking plate</td><td>Alteration of ankle pressure by DFO and HTO</td><td>92.3 %</td></tr><tr><td>Kuwashima et al. [40]</td><td>Finite element</td><td>Axial stability and risk of fracture</td><td>Bi-planar MCW-DFO</td><td>Locking plate Hinge fixator screw and plate</td><td>Improvement of stability by adding hinge fixators in case of hinge fracture</td><td>80.8 %</td></tr><tr><td>Lian et al. [41]</td><td>Observational (retrospective)</td><td>Hinge fracture</td><td>Bi-planar MCW-DFO</td><td>Locking plate</td><td>Increased risk of hinge fracture in supracondylar positions</td><td>92.3 %</td></tr><tr><td>Liles et al. [59]</td><td>Experimental (Cadaveric)</td><td>Knee contact pressure</td><td>Uni-planar LOW- and MCW-DFOs</td><td>Locking plate</td><td>Decreased contact pressure in lateral compartment after LOW-DFO</td><td>96.2 %</td></tr><tr><td>Maione et al. [65]</td><td>Experimental (retrospective)</td><td>Ankle alignment</td><td>Bi-planar MCW-DFO</td><td>Locking plate</td><td>Alteration in ankle alignment after DFO</td><td>92.3 %</td></tr><tr><td>Matsushita et al. [31]</td><td>Experimental (Cadaveric)</td><td>Axial and torsional stability in flexion and extension</td><td>Uni-planar MCW-DFO</td><td>Locking plate Hinge fixator screw and plate</td><td>Hinge fractures caused abnormal hinge movements</td><td>92.3 %</td></tr><tr><td>Meisterhans et al. [23]</td><td>Finite element</td><td>Risk of hinge fracture</td><td>Bi-planar LOW- and MCW-DFOs</td><td>N/A</td><td>Higher risk of fracture in MCW compared to LOW</td><td>84.0 %</td></tr><tr><td>Meisterhans et al. [24]</td><td>Experimental (porcine femurs)</td><td>Risk of hinge fracture</td><td>Uni-planar LOW- and MCW-DFOs</td><td>N/A</td><td>Higher allowable correction using MCW compared to LOW</td><td>88.5 %</td></tr><tr><td>Mereb et al. [7]</td><td>Experimental (3D-printed femur)</td><td>Risk of hinge fracture</td><td>Uni-planar LOW-DFO</td><td>N/A</td><td>Reduced risk of hinge fracture by adding a k-wire inside hinge</td><td>92.3 %</td></tr><tr><td>Monteiro et al. [66]</td><td>Experimental (retrospective)</td><td>Ankle alignment and pain</td><td>Bi-planar MCW- and LCW-DFOs</td><td>Locking plate</td><td>Adjustments in the ankle and hindfoot alignment after DFO</td><td>92.3 %</td></tr><tr><td>Nha et al. [18]</td><td>Experimental (cadaveric)</td><td>Risk of hinge fracture</td><td>Uni-planar MCW-DFO</td><td>N/A</td><td>Lower risk of hinge fracture with in condylar region</td><td>84.6 %</td></tr><tr><td>Nha et al. [21]</td><td>Experimental (retrospective)</td><td>Risk of hinge fracture</td><td>Bi-planar MCW-DFO</td><td>Locking plate</td><td>Higher incidence of hinge fracture in supracondylar region</td><td>80.8 %</td></tr><tr><td>Nha et al. [64]</td><td>Experimental (retrospective)</td><td>Ankle and hindfoot alignment</td><td>Bi-planar MCW-DFO</td><td>Locking plate</td><td>DFO Correction propagates distally but is mitigated by subtalar compensation</td><td>73.1 %</td></tr><tr><td>Oda et al. [33]</td><td>Experimental (cadaveric)</td><td>Soft tissue stabilization in hinge fracture</td><td>Bi-planar MCW-DFO</td><td>N/A</td><td>Presence of a thick periosteum at the metaphysis supporting lateral hinge stability</td><td>80.8 %</td></tr><tr><td>Oda et al. [34]</td><td>Experimental (cadaveric)</td><td>Soft tissue stabilization in hinge fracture</td><td>Bi-planar LCW-DFO</td><td>N/A</td><td>Presence of a thick periosteum at the metaphysis supporting medial hinge stability</td><td>80.8 %</td></tr><tr><td>Ogawa et al. [48]</td><td>Experimental (composite femur)</td><td>Axial stability</td><td>Bi-planar LOW-Bi-planar MCW</td><td>Locking plate Bone substitute graft for gap filling</td><td>Higher axial stability of LOW-DFO compared to MCW-DFO</td><td>80.8 %</td></tr><tr><td>Peez et al. [32]</td><td>Experimental (Cadaveric)</td><td>Axial and torsional stability</td><td>Uni- and bi-planar LOW- and MCW-DFOs</td><td>Locking plate Hinge fixator screw and plate</td><td>Reduced rotational stability due to hinge fracture both in LOW-DFO and MCW-DFO</td><td>96.2 %</td></tr></tbody></table>

(continued on next page)
<table><caption>**Table 2 (continued)**</caption><thead><tr><th>Study (A to Z)</th><th>Type</th><th>Focus</th><th>DFO technique</th><th>Fixation</th><th>Main finding</th><th>Kmet score</th></tr></thead><tbody><tr><td>Pietsch et al. [44]</td><td>Experimental (composite femur)</td><td>Axial and torsional stability</td><td>Uni-planar LOW Bi-planar LOW</td><td>Locking plate</td><td>No significant difference in axial and torsional stiffness between uni- and bi-planar LOW-DFO</td><td>88.5 %</td></tr><tr><td>Quirno et al. [56]</td><td>Experimental (Cadaveric)</td><td>Contact measures in knee compartments</td><td>(N/R) LOW-DFO</td><td>Locking plate Bone substitute graft for gap filling</td><td>Recommendation of over-correction to achieve normal load distribution in knee</td><td>76.9 %</td></tr><tr><td>Risser et al. [39]</td><td>Experimental (3D-printed femur)</td><td>Risk of hinge fracture</td><td>Uni-planar LOW-DFO</td><td>N/A</td><td>Lower risk of hinge fracture with a central position of protective hinge wire</td><td>92.3 %</td></tr><tr><td>Rupp et al. [26]</td><td>Observational (retrospective)</td><td>Risk of hinge fracture</td><td>Bi-planar LCW-DFO</td><td>Locking plate</td><td>Enlarged medial cortical bridge is linked to higher rate of hinge fracture</td><td>96.2 %</td></tr><tr><td>Schröter et al. [60]</td><td>Retrospective (of 52 DFOs)</td><td>Anatomical changes in knee</td><td>Uni-planar MCW-DFO</td><td>Locking plate</td><td>Negative effect of over-correction due to oblique joint line after MCW-DFO</td><td>84.6 %</td></tr><tr><td>Simon et al. [49]</td><td>Observational (prospective)</td><td>Risk of hinge fracture</td><td>LOW- and MOW-DFOs</td><td>Angle blade plate</td><td>Higher hinge fracture risk with enlarged medial cortical bridge</td><td>96.2 %</td></tr><tr><td>Teo et al. [22]</td><td>Observational (retrospective)</td><td>Risk of hinge fracture</td><td>Bi-planar LCW- and MCW-DFOs</td><td>Locking plate</td><td>Reduced risk when hinge placed at the level of the inferior metaphyseal flare</td><td>92.3 %</td></tr><tr><td>van der Woude et al. [46]</td><td>Observational (retrospective)</td><td>Bone healing time</td><td>Uni- and bi-planar LCW-DFOs</td><td>Locking plate</td><td>Faster bone healing in bi-planar technique compared to uni-planar</td><td>76.9 %</td></tr><tr><td>van Egmond et al. [62]</td><td>Observational (retrospective)</td><td>Gait analysis</td><td>MCW-DFO LCW-HTO</td><td>Angular stable plate</td><td>Gait improvement (closer to healthy gate) after varus producing osteotomies</td><td>88.5 %</td></tr><tr><td>van Heerwaarden et al. [45]</td><td>Experimental (composite femurs)</td><td>Bone contact area and wedge volume</td><td>Uni- and bi-planar LOW- and MCW-DFOs</td><td>N/A</td><td>Larger bone contact area in bi-planar and smallest wedge volume for MCW</td><td>92.3 %</td></tr><tr><td>Winkler et al. [16]</td><td>Observational (retrospective)</td><td>Incidence and morphology of hinge fracture</td><td>(N/R) LOW-DFO</td><td>N/A</td><td>Hinge locations at the level of or distal to adductor tubercle recommended to reduce the risk of fracture</td><td>96.2 %</td></tr><tr><td>Wu et al. [5]</td><td>Finite element</td><td>Contact measures in knee compartments</td><td>Uni-planar LOW-DFO</td><td>N/A</td><td>high over-correction not recommended due steep increase of stress in medial compartment</td><td>80.8 %</td></tr><tr><td>Wylie et al. [58]</td><td>Experimental (Cadaveric)</td><td>Contact measures in knee compartments</td><td>(N/R) LOW-DFO</td><td>Contour lock plate</td><td>Decreased contact pressure in lateral compartment after LOW-DFO</td><td>92.3 %</td></tr><tr><td>Yildirim et al. [27]</td><td>Experimental (composite femur)</td><td>Risk of hinge fracture</td><td>Uni- and bi-planar LOW-DFOs</td><td>N/A</td><td>Lower risk of hinge fracture in bi-planar LOW-DFO compared to uni-planar</td><td>80.8 %</td></tr></tbody></table>

N/A : Not Applicable.

N/R : Not Reported.

et al. [23,24] also reveal that the type of distal femoral osteotomy itself markedly affects the likelihood of hinge fracture. In their finite element simulations, the MCW configuration exhibited consistently higher cortical strain and fracture risk than the LOW setup under identical hinge dimensions and correction magnitudes. This difference was attributed to the larger hinge cross-sectional area on the medial side, which limits plastic deformation and concentrates tensile stresses. Conversely, in the subsequent porcine biomechanical experiments, MCW osteotomies withstood substantially greater angular correction before failure (13° versus 7° for LOW), indicating greater resistance to fracture under compressive loading. These opposing trends suggest that hinge stability depends not only on geometry but also on the different loading modes (tensile in LOW versus compressive in MCW) which govern how the bone accommodates deformation and fracture.

### Uni- vs. bi-planar cuts

Yildirim et al. [27] compared uni-planar and bi-planar LOW-DFO using synthetic composite femora to evaluate the risk of medial hinge fracture during gap opening. Although the bi-planar osteotomies withstood slightly higher loads and allowed marginally greater wedge openings before fracture, neither difference reached statistical significance. The authors noted that the second anterior cut in the bi-planar configuration altered the cross-sectional geometry and tended to redirect the fracture line proximally, resulting more often in type 3 hinge fractures, whereas the uni-planar cuts typically produced type 1 extensions of the osteotomy plane. It is worth mentioning that the composite bone models used in their work reproduces the geometry of the human distal femur but not its mechanical properties, limiting physiological interpretation.

### Cut Angle Considerations

The influence of the osteotomy cut angle on hinge fracture risk has not yet been investigated in the context of DFO. However, two finite element studies in HTO suggest that while the cut angle may not directly

affect fracture risk, it does alter the magnitude of force required to open the osteotomy gap [28,29]. Future investigations should consider this parameter in the biomechanical evaluation of DFO techniques.

### 3.2.4. Influence of hinge fracture on the stability of correction

Hinge fractures compromise the mechanical stability of distal femoral osteotomy (DFO) corrections. In a biomechanical study using synthetic femora, Batista et al. [30] demonstrated that a fractured medial hinge markedly reduces both axial compressive and rotational stiffness in LOW-DFO. Comparable findings were reported by Matsushita et al. [31] in MCW-DFO, where hinge disruption significantly increased translation and rotation at the osteotomy site, indicating reduced structural integrity. More recently, Peez et al. [32] evaluated the effect of hinge fracture in both LOW and MCW configurations, confirming greater rotational displacement and reduced rotational stiffness. Although axial stiffness was not significantly altered, axial displacement increased, suggesting localized instability along the hinge axis.

Clinically, Fujita et al. [19] reported a high incidence of hinge fracture (57 %) in MCW-DFO and demonstrated its negative effect on bone healing. Delayed union beyond three months occurred in 67 % of patients with hinge fractures compared with only 11 % without fracture and correction loss of 2° or more was observed in 67 % of delayed-healing cases. These findings emphasize that hinge fracture substantially impairs mechanical stability and subsequent consolidation.

While most previous studies assessed hinge behaviour after fixation, Nha et al. [18] evaluated immediate post-osteotomy stability by measuring lateral hinge displacement under manual varus-valgus loading before fixation. They observed that only MCW-DFOs with a supracondylar hinge exhibited significant instability following fracture, whereas those with a condylar hinge maintained mechanical resistance. These findings underscore the critical influence of hinge location on
post-fracture stability and further support the condylar region as a preferred site for hinge placement.

### 3.2.5. Soft tissue stabilization post-fracture

Cadaveric and histological analyses have shown that soft-tissue attachments on the lateral femur can contribute to hinge stabilization after fracture. For a lateral hinge (MCW-DFO in this case), Kim et al. [20] identified the femoral attachment of the lateral head of the gastrocnemius as a key stabilizer covering the posterolateral cortex of the distal femur. When the hinge was located within this attachment, none of the osteotomies developed unstable fractures. Oda et al. [33] confirmed these findings by quantifying periosteal and capsular attachments on the distal lateral femur. They found that the periosteum thickens at the metaphyseal–diaphyseal transition, forming a zone capable of supporting minor hinge disruption. Both studies converge in defining a narrow “safe zone” extending from the apex of the femoral metaphyseal turn to the upper border of the posterior lateral condyle, where soft-tissue continuity may prevent displacement even in the presence of a hinge fracture.

For a medial hinge (in a LCW-DFO), Oda et al. [34] demonstrated that the periosteum and the adductor tendon (AT) provide significant stabilizing potential for the hinge. Histological sections revealed a thick periosteum at the metaphysis and a direct fibrocartilaginous insertion of the AT, forming a soft-tissue envelope capable of maintaining fracture apposition. Pilot osteotomies confirmed that even when the hinge was intentionally fractured, the AT–periosteum complex maintained alignment without dislocation. The authors thus defined a medial “safe zone” bounded by the adductor tubercle and the posterior border of the medial condyle, within which hinge fractures are less likely to propagate. This finding aligns with previous works by Rupp et al. [26] and Winkler et al. [16], which reported fewer medial hinge fractures when the hinge was placed at or distal to the adductor tubercle.

### 3.2.6. Hinge preservation techniques

Only a limited number of studies have specifically addressed strategies to prevent hinge fractures. Recent advances in patient-specific cutting guides have enabled the placement of a Kirschner wire (K-wire) within the hinge zone to reinforce the cortex during osteotomy opening or closing [35]. The protective effect of such “hinge wires” was initially demonstrated in HTO [36]. Extending this concept to DFO, Mereb et al. [7] performed a biomechanical study on 3D-printed distal femur models to assess the influence of hinge wire on medial hinge fracture risk during LOW-DFO. The insertion of a K-wire within the hinge region significantly increased the maximum opening force prior to fracture, thereby reducing the likelihood of cortical failure. The authors also examined the effect of opening speed but found no statistically significant difference in fracture occurrence. However, this finding should be interpreted with caution, as the viscoelastic behaviour of the ABS material used in the printed models may differ substantially from that of human bone.

Recent FE studies have further supported the protective role of hinge reinforcement using a hinge wire, while highlighting that its effectiveness depends on several geometric and positional parameters. In a study on LOW-DFO, Baris et al. [37] reported that a 1.6-mm wire provided superior structural reinforcement and more favourable stress distribution than a 2.5-mm wire. Similarly, Dastgerdi et al. [38] using a finite element model of MCW-DFO, found that inserting the wire at a 60° angle relative to the horizontal plane minimized fracture risk by reducing both tensile/compressive stresses and the plasticly deformed volume near the hinge. In addition, another experimental study [39] (with an identical study design and setup used in Mereb et al. [7]) demonstrated that positioning the wire centrally along the anteroposterior axis of the hinge yielded the highest maximum opening force before fracture, out-performing anterior or posterior placements.

### 3.2.7. Treatment of fractured hinge

In cases where a hinge fracture occurs, hinge support fixators can be employed to restore stability and maintain correction. Batista et al. [30] investigated the effect of adding a medial cancellous screw to compensate for the loss of stability caused by medial hinge fracture in LOW-DFO. Their results showed that screw reinforcement restores construct stiffness to levels comparable to an intact hinge. In a similar context, Matsushita et al. [31] evaluated two reinforcement techniques in uni-planar MCW-DFO, a single hinge screw and a short support plate and reported reductions in translational and rotational motion at the fracture site, although the improvement from screw fixation alone was not statistically significant. Complementary findings were reported by Kuwashima et al. [40] through finite element modelling, which demonstrated enhanced hinge stability with both screw and plate support. Consistent with these observations, Peez et al. [32] conducted a cadaveric study comparing the two reinforcement methods across both LOW-DFO and MCW-DFO, including uni- and bi-planar osteotomy designs. Their results confirmed increased axial and rotational stiffness with hinge fixators, with the locking plate providing superior stabilization compared to screw fixation.

### 3.2.8. Post-surgery hinge fractures

Hinge fracture may also occur postoperatively, rather than during the osteotomy itself. Lian et al. [41] reported an overall hinge fracture incidence of 33 % (in a cohort of 87 patients), comprising intraoperative fractures in 15 % of cases and postoperative fractures in 18 % following LOW-DFO. Their analysis identified hinge position as the principal determinant of postoperative fracture risk, suggesting that hinges placed proximal to the adductor tubercle (supracondylar region) were associated with a 10- to 15-fold higher risk of fracture compared with those positioned at the level of the adductor tubercle. However, postoperative fractures did not significantly delay bone healing.

A finite element analysis by Higa et al. [42] on bi-planar medial closing-wedge DFO under simulated full weight-bearing conditions further demonstrated that adding positional mono-cortical or bi-cortical screws traversing the hinge markedly reduced local stresses, thereby lowering the likelihood of postoperative hinge fracture. The protective effect of mono-cortical screws, however, was highly dependent on trabecular bone quality, suggesting that their benefit may be limited in osteoporotic bone, whereas bi-cortical configurations provided consistent reinforcement regardless of bone density.

## 3.3. Correction stability

### 3.3.1. Influence of cut geometry on stability: uni- vs bi-planar cuts

Regarding short-term stability, several biomechanical investigations have compared uni- and bi-planar osteotomy configurations in DFO. Brinkman et al. [43] reported that in MCW-DFO, the bi-planar cut increased axial stiffness through greater cortical contact but slightly reduced torsional stability, reflecting a trade-off between compressive resistance and rotational control. In contrast, Pietsch et al. [44] found in LOW-DFO that the osteotomy geometry did not significantly influence primary axial or torsional stiffness under intact conditions; however, the bi-planar configuration showed higher torsional resistance when a medial cortical fracture was simulated, suggesting improved mechanical resilience in compromised hinges. Similarly, Peez et al. [32] observed that bi-planar osteotomies produced smaller hinge displacements and moderately greater torsional stability in both MCW- and LOW-DFO, although differences were not statistically significant. Collectively, these findings indicate that while bi-planar cuts may offer modest mechanical advantages, particularly in maintaining rotational stability and hinge integrity, their influence on overall short-term construct stiffness remains limited.

Regarding long-term outcomes, several studies have shown that osteotomy geometry also influences bone healing and cortical contact following DFO. Van Heerwaarden et al. [45] demonstrated that the
bi-planar configuration provides a larger cancellous contact surface and a smaller wedge volume than the uniplanar design, thereby enhancing primary bone contact and promoting more favourable conditions for direct cortical healing. These geometric advantages were reflected clinically in the findings of van der Woude et al. [46], who reported a significantly shorter time to union for bi-planar osteotomies (4 ± 3 months) compared with uniplanar ones (6 ± 3 months), while maintaining equivalent correction accuracy. Collectively, these results suggest that bi-planar osteotomies facilitate faster and more reliable bone union by increasing the contact area and improving the mechanical and biological environment for healing.

The angle of osteotomy may also influence the stability of DFO. Brinkman et al. [47] found that an oblique osteotomy cut is more stable (especially in torsion) than the perpendicular one due to the larger contact area after closing of the wedge in MCW-DFO. However, the research on the influence of angle of obliquity on the stability is limited.

### 3.3.2. Influence of DFO technique on stability: open vs. closed wedge

Few biomechanical studies exist in the literature that compare the LOW and MCW techniques. Brinkman et al. [47] conducted a biomechanical comparison using composite femur models. They found that MCW-DFOs were significantly stiffer and more stable than LOW-DFOs under both axial and torsional loading. The open-wedge configuration showed reduced load-bearing capacity due to the lateral gap and loss of cortical continuity. In contrast, Ogawa et al. [48] found the opposite trend, with LOW-DFO demonstrating higher stability and failure strength than MCW-DFO. This discrepancy was primarily explained by methodological differences. Brinkman et al. used early-generation fixation plates without graft augmentation, while Ogawa et al. employed locking plates combined with β-TCP bone grafts, which markedly enhanced construct stiffness and load distribution across the osteotomy gap.

To date, the choice between open- and closed-wedge DFO techniques remains controversial and depends on the opinion of the expert planning the intervention. Clinical evidence from Simon et al. [49] indicates that when fixation and biological conditions are adequate, the type of osteotomy (open- or closed wedge) does not significantly influence bone healing outcomes.

While the lateral open-wedge technique in DFO is widely used for valgus deformities, there is limited data on medial open-wedge (MOW) DFO techniques for varus deformities. In an experimental study on composite bones, Karkosch et al. [50] showed that MOW-DFO yields comparable axial and torsional stability to LOW-DFO.

### 3.3.3. Influence of fixation method on stability: locking plate vs. angle blade plate

Locking plates and angled blade plates are the two main fixation methods used in DFO. The angled blade plate, historically employed in orthopaedic surgery, consists of a plate with a fixed blade inserted into the bone at a defined angle, providing strong fixation through precise mechanical engagement. Locking plates, in contrast, are designed with threaded holes that allow screws to lock into the plate, creating a fixed-angle construct that stabilizes bone segments during corrective osteotomies. A first biomechanical comparison between these two methods was carried out by Brinkman et al. [47], who demonstrated the superior stiffness and stability of angled blade plates over locking plates in MCW-DFO. Similarly, Batista et al. [30] found that LOW-DFOs fixed with angled blade plates exhibited greater axial and torsional stability than those with locking plates, especially when combined with hinge-fixator screws. From a clinical standpoint, although angled blade plate fixation is technically more demanding, it remains a more affordable alternative to locking plates [51].

While these studies primarily evaluated immediate postoperative stability, the long-term biomechanical performance of fixation systems during bone healing remains less explored. Olivero et al. [52] reported that locking plates provide greater early-stage stability, especially in

osteoporotic bone or large corrections, by minimizing micromotion and correction loss. However, they found no clear long-term advantage over angled blade plates, as both systems achieve comparable alignment maintenance and functional outcomes once healing is complete. This suggests that fixation choice should be guided by patient-specific factors such as bone quality, correction magnitude and surgical expertise.

### 3.3.4. Influence of gap filling on stability

Following gap opening in LOW-DFO, various bone grafting materials, including autografts, allografts and synthetic substitutes, may be employed to support bone healing, as noted in [15,48]. While autografts remain the gold standard due to their osteogenic potential and favourable healing rates [53], their use is generally limited to larger corrections. Synthetic fillers such as β-TCP, hydroxyapatite, or calcium phosphate have shown promising clinical outcomes in moderate gaps but vary in biomechanical reliability [54]. Importantly, biomechanical investigations remain limited. A recent cadaveric study on HTO demonstrated that structural allograft wedges enhance construct stiffness, particularly in large corrections (>10°) [55], indicating a stabilizing role during the early post-operative phase. However, the influence of graft material properties on micromotion at the osteotomy site remains largely unexplored. Future studies should aim to clarify how these material-dependent mechanical behaviours affect healing in LOW-DFO.

## 3.4. Correction outcomes

### 3.4.1. Influence of DFO on knee joint loading

The primary objective of osteotomy is to restore the physiological mechanical axis and unload the damaged knee compartment. In a cadaveric study, Quirno et al. [56] investigated the effect of LOW-DFO on load distribution in valgus knees and reported a 25 % decrease in mean contact pressure together with a 20 % reduction in both peak contact pressure and mean contact area within the lateral compartment after correction. A finite element analysis by Wu et al. [5] corroborated these findings, showing decreases in peak von Mises stress and peak shear stress in the lateral compartment following LOW-DFO. Consistent with these experimental and computational results, Hamasaki et al. [57] observed a similar trend clinically in MCW-DFO. Using subchondral bone density as an indirect measure of stress distribution, they reported a reduction in lateral compartment stress and a restoration of more balanced tibiofemoral load transfer toward the medial side.

In a cadaveric study, Wylie et al. [58] investigated load redistribution following LOW-DFO by measuring compartmental contact forces across varying degrees of knee flexion. They found that the reduction in lateral compartment load was most pronounced in full extension and diminished progressively with increasing flexion. The authors suggested that, because functional activities of daily living generally involve limited flexion angles, LOW-DFO effectively unloads the lateral compartment under typical physiological conditions. A more recent cadaveric study by Liles et al. [59] corroborated these findings but observed smaller magnitudes of pressure change, which were likely due to differences in correction angle (8° vs. 10 to 12° in [58]) and loading protocol (300 N vs. 1000 N).

### 3.4.2. Optimal correction degree

All studies discussed in Section 3.4.1 consistently demonstrated that increasing the correction angle in LOW-DFO progressively unloads the lateral tibiofemoral compartment. However, the optimal degree of correction remains a subject of debate among surgeons. Quirno et al. [56] recommended an overcorrection of approximately 5°, arguing that this level of adjustment more effectively restores near-normal contact pressure in the lateral compartment compared with correction to a neutral mechanical axis. In contrast, the finite element analysis by Wu et al. [5] advocated for a nearly neutral varus correction (0° to 2° overcorrection), reporting that overcorrections beyond 2° markedly increase stress within the medial compartment and may predispose to
medial compartment osteoarthritis.

A recent retrospective study [60] on MCW-DFO also confirmed that overcorrection of the mechanical lateral distal femoral angle (mLDFA) should be avoided, as this may induce joint-line obliquity and alter knee biomechanics. Moreover, several reports have indicated that corrective osteotomies performed for valgus or varus malignment can influence adjacent joint mechanics, notably by increasing the hip abduction angle or modifying ankle alignment, which may lead to postoperative pain or discomfort [61].

### 3.4.3. Influence of correction on gait

Valgus malignment of the knee and the corrective osteotomies performed to restore alignment such as DFO, can substantially influence gait mechanics. In a prospective gait analysis, van Egmond et al. [62] compared 12 patients with valgus deformity to 10 healthy controls, both before and after correction using tibial, femoral, or double-level osteotomy. Preoperatively, patients demonstrated reduced knee and hip flexion-extension angles and joint moments compared with controls, reflecting limited dynamic mobility and altered load transfer. The valgus alignment also produced an abnormally low knee adduction moment, indicative of excessive lateral compartment loading. Following surgical realignment, the adduction moment increased toward normal values, signifying a medial shift in dynamic knee loading and partial restoration of physiological gait patterns.

DFO can also contribute to restoring stability in valgus knees with ligament insufficiency. In a cadaveric gait study, Hetsroni et al. [63] demonstrated that in valgus knees with medial collateral ligament (MCL) and anterior cruciate ligament (ACL) deficiencies, LOW-DFO may improve medial knee stability by reducing valgus moments during gait and potentially providing a secondary medial tensioning effect. These findings suggest that LOW-DFO may enhance medial stability in valgus knees with combined ligament laxity and serve as a biomechanical adjunct to ligament reconstruction.

### 3.4.4. Influence of correction on ankle

Radiographic studies consistently show that DFO alters coronal ankle alignment as the mechanical axis correction propagates distally. Korrads et al. [61] reported significant changes in malleolar orientation after both varus- and valgus-producing osteotomies. However, Nha et al. [64] found that hindfoot alignment tends to normalize toward neutrality by a compensatory subtalar adaptation, preventing major ankle malalignment. Similarly, Maione et al. [65] and Monteiro et al. [66] demonstrated that DFO significantly modifies the tibiototal inclination and distal tibial alignment. These findings suggest that realignment at the knee induces measurable but mostly compensable adjustments in the ankle and hindfoot, largely mitigated by subtalar motion.

The effect of DFO on joint loading and postoperative discomfort appears to be dependent on the degree of correction and the compensatory capacity of adjacent joints. Monteiro et al. [66] observed that larger correction angles were associated with increased alteration of tibial plafond inclination, occasionally accompanied by ankle pain. Krause et al. [67] further reported that excessive valgus correction may elevate distal joint stresses, leading to postoperative ankle pain.

## 3.5. Methodological approaches

A thorough understanding of the biomechanics of DFO requires robust experimental and numerical methodologies to ensure reliable and clinically relevant findings. This section discusses key methodological aspects of the experimental (summarized in Table 3) and numerical (summarized in Table 4) studies included in this review, including the choice of bone models, test designs and the outcome measures used to assess biomechanical performance.

### 3.5.1. Bone model

Among the experimental studies reviewed, two primary types of

<table><caption>**Table 3**
Summary of experimental studies in DFO.</caption><thead><tr><td>Study</td><td>Material</td><td>Loading condition</td><td>Measured parameter</td></tr></thead><tbody><tr><td>Batista et al. [30]</td><td>Synbone® femurs</td><td>Non-destructive axial and torsional loading</td><td>Global force-displacement and moment/rotation</td></tr><tr><td>Brinkman et al. [43, 47]</td><td>Third and fourth-generation Sawbones® femurs</td><td>Axial and torsional cyclic loading followed by failure test</td><td>Micromotions and global force/ moment-displacement</td></tr><tr><td>Karkosch et al. [50]</td><td>Sawbones® femurs (Generation not mentioned)</td><td>Axial and torsional cyclic loading followed by failure test</td><td>Global force/ moment-displacement</td></tr><tr><td>Krause et al. [67]</td><td>Cadaveric limbs</td><td>Axial loading in full extension of knee</td><td>Contact pressure inside ankle</td></tr><tr><td>Liles et al. [59]</td><td>Cadaveric knees</td><td>Axial loading in different extension angles of knee</td><td>Contact pressure inside knee compartments</td></tr><tr><td>Matsushita et al. [31]</td><td>Cadaveric limbs</td><td>Cyclic axial loading at maximum and 45° extension of knee</td><td>Motion capture and strain</td></tr><tr><td>Meisterhans et al. [24]</td><td>Porcine femurs</td><td>DFO cut opening/ closing</td><td>Global force-displacement</td></tr><tr><td>Mereb et al. [7]</td><td>3D printed femurs</td><td>DFO cut opening by applying load on diaphysis up to failure</td><td>Global force-displacement</td></tr><tr><td>Ogawa et al. [48]</td><td>Fourth-generation Sawbones® femurs</td><td>Axial cyclic loading followed by failure test</td><td>Global load-displacement and local strain in hinge area</td></tr><tr><td>Peez et al. [32]</td><td>Cadaveric femurs</td><td>Cyclic axial and torsional load</td><td>Motion capture and stiffness</td></tr><tr><td>Pietsch et al. [44]</td><td>Fourth-generation Sawbones® femurs</td><td>Cyclic axial and torsional load</td><td>Motion capture and stiffness</td></tr><tr><td>Quirno et al. [56]</td><td>Cadaveric knees</td><td>Axial loading in full extension of knee</td><td>Contact pressure inside knee compartments</td></tr><tr><td>Risser et al. [39]</td><td>3D printed femurs</td><td>DFO cut opening by applying load on diaphysis up to failure</td><td>Global force-displacement</td></tr><tr><td>Wylie et al. [58]</td><td>Cadaveric knees</td><td>Anatomical loading using quadriceps at different extension angles of knee</td><td>Contact pressure inside knee compartments</td></tr><tr><td>Yildirim et al. [27]</td><td>Selbone® composite femurs</td><td>DFO cut opening using a wedge shape separator</td><td>Global force-displacement and gap opening</td></tr></tbody></table>

bone models were employed: cadaveric specimens and synthetic composite bones. While cadaveric models remain essential for biomechanical investigations, they are subject to substantial inter-specimen variability, often necessitating larger sample sizes to achieve statistical significance. Moreover, cadaveric samples are typically sourced from elderly donors (e.g., median ages of 75 and 79 years in [31] and [32], respectively), which poses a limitation for DFO studies. Since bone quality significantly affects fixation stability, age-related reductions in bone density may compromise the generalizability of findings to the younger, more active population commonly undergoing DFO.

In contrast, composite bone models offer consistent material properties and reduce variability across samples. Their mechanical characteristics have been shown to approximate those of healthy young adult femora [68], aligning more closely with the target demographic for DFO. However, these models do not replicate the contribution of soft tissue structures, which have been shown to affect construct stability, particularly in the context of hinge fracture. Additionally, the absence of viscoelastic behaviour may limit their accuracy in simulating dynamic loading conditions and results derived from such models should be
<table><caption>**Table 4**
Summary of numerical studies in DFO.</caption><thead><tr><td>Study (A to Z)</td><td>Geometry</td><td>Material</td><td>Outcome measures</td></tr></thead><tbody><tr><td>Baris et al. [37]</td><td>Distal femur-only model based on CT of one patient</td><td>- Linear isotropy based on HU of CT images</td><td>Principal strain and stress in the hinge area</td></tr><tr><td>Dastgerdi et al. [38]</td><td>Distal femur-only model based on CT of one patient</td><td>- Linear isotropy based on HU of CT images</td><td>Principal strain and stress in the hinge area</td></tr><tr><td>Higa et al. [42]</td><td>Commercial distal femur-only model</td><td>- Linear isotropy both for cortical and trabecular bone</td><td>Shear stress around the hinge area</td></tr><tr><td>Inacio et al. [70]</td><td>Femur-only model based on CT of one patient</td><td>- Linear isotropy based on HU of CT images</td><td>Axial stiffness of bone-implant construct</td></tr><tr><td>Kuwashima et al. [40]</td><td>Distal femur-only model based on CT of five patients</td><td>- Linear isotropy based on HU of CT images</td><td>Von-Mises stress inside hinge area and fixation plate</td></tr><tr><td>Meisterhans et al. [23]</td><td>Distal femur-only model based on reconstruction of 61 postmortem CT-scans</td><td>- Transverse isotropy for cortical bone - Linear isotropy for trabecular bone</td><td>Tensile and compressive strain at hinge area</td></tr><tr><td>Wu et al. [5]</td><td>Full lower limb model based on CT-scan and MRI of one patient</td><td>- Linear isotropy for all materials (bone considered as a single material)</td><td>Von-Mises stress for cartilage damage and meniscal tear</td></tr><tr><td></td><td></td><td></td><td>Shear stress for cartilage degeneration</td></tr></tbody></table>

interpreted with these limitations in mind.

Regarding the numerical studies, the definition of bone material properties plays a critical role in the accuracy of results. Several studies, including [5] and [42], have modelled bone as an isotropic linear elastic material, which may not adequately capture its anisotropic behaviour under complex loading conditions. Incorporating more realistic constitutive models can enhance predictive accuracy. For instance, Meisterhans et al. [23] applied transversely isotropic properties for cortical bone, providing a closer approximation of its true mechanical response. In simulations addressing hinge fracture [23,42], the use of linear elasticity has yet to be coupled with damage or rupture mechanics. Techniques such as the extended finite element method (XFEM), successfully applied to simulate crack propagation in open-wedge HTO by Saghaei and Hashemi [69], have not yet been implemented in the context of DFO.

### 3.5.2. Test design

Accurate replication of physiological or surgical loading and boundary conditions is critical in experimental studies to ensure that findings are both reliable and translational to clinical practice.

Various experimental configurations have been adopted to assess the stability of DFO. Brinkman et al. [47] employed a setup (Fig. 3) in which both the femoral head and distal femur were embedded in cold-curing resin and mounted in a material testing system using a custom fixture. This configuration simulated the post-correction alignment of a normally loaded knee and enabled the application of axial and torsional loads. Similarly, Peez et al. [32] used a customized fixture for cadaveric specimens to replicate post-operative conditions. In contrast, Ogawa et al. [48] integrated the tibia into their test assembly, bypassing the need for specialized fixtures and more realistically reproducing the knee joint by using cork board as a meniscus surrogate. A finite element study by Inacio et al. [70] highlighted the substantial influence of fixation constraints on measured mechanical behaviour: rigid potting of femoral

<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Experimental protocol used by Brinkman et al. [43,47]<fnref n="1" /> showing the testing machine setup (left) and ultra-sound motion capture system (right). Reprinted from *Knee Surgery, Sports Traumatology, Arthroscopy*, Vol 19, Issue 7, Brinkman et al., "Axial and torsional stability of an improved single-plane and a new bi-plane osteotomy technique for supracondylar femur osteotomies", Copyright (2010), with permission from John Wiley and Sons.</figcaption></figure>

ends was shown to increase axial stiffness by up to 25-fold, potentially distorting physiological relevance. More recently, Matsushita et al. [31] utilized intact cadaveric knees, allowing for the application of realistic joint loads and developed a fixture capable of testing the joint in flexed positions, thereby further enhancing physiological fidelity.

In studies analysing joint unloading after DFO, both Quirno et al. [56] and Wylie et al. [58] employed cadaveric specimens but used distinct experimental setups that influence interpretation. Quirno attached a cadaveric proximal femur to a composite distal femur and applied axial load to simulate full extension, focusing on static conditions without soft tissue contributions. In contrast, Wylie et al. preserved the entire limb with quadriceps intact and used a custom fixture to assess tibiofemoral contact pressures across multiple flexion angles under static muscle loading. These methodological differences are critical: while Quirno's model offered a simplified view of load transmission in extension, Wylie's approach better captured the joint's mechanical response under functional, dynamic conditions. The latter found that LOW-DFO most effectively unloaded the lateral compartment in full extension, with reduced efficacy in flexion, underscoring the importance of incorporating soft tissue forces and knee kinematics in biomechanical evaluations.

Among studies investigating hinge fracture, variations in osteotomy gap-opening techniques represent a critical yet underexplored factor. During opening-wedge osteotomies, surgeons typically use either a chisel or a mechanical distractor to separate the osteotomy surfaces. Meisterhans et al. [23] simulated the use of a distractor in their finite element model by fixing the proximal femur and applying a force at the cut border (Fig. 4). In contrast, Yildirim et al. [27] reproduced the chisel

<footnote n="1">¹ Reprinted from Brinkman et al. (2010) with permission. Original source DOI: 10.1007/s00167-010-1349-0.</footnote>

<footnote n="2">² Reprinted from Meisterhans et al. (2023) under the Creative Commons Attribution International License (CC BY 4.0). Original source DOI: 10.1186/s40634-023-00597-w.</footnote>
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** Finite element model developed by² Meisterhans et al. [23] to analyse the risk of hinge fracture. Reprinted from *Journal of Experimental Orthopaedics*, Meisterhans et al., "Finite element analysis of medial closing and lateral opening wedge osteotomies of the distal femur in relation to hinge fractures", 2023. Distributed under the terms of the Creative Commons CC BY license.</figcaption></figure>

technique by inserting a wedge-shaped metal separator between the osteotomy planes. Meanwhile in Mereb et al. [7], the opening force was applied to the diaphyseal region of the proximal femur, with the distal epiphysis rigidly fixed (Fig. 5), a setup designed to improve inter-specimen reproducibility. Despite these methodological differences, no study to date has systematically examined the biomechanical impact of gap-opening strategies on hinge fracture risk.

### 3.5.3. Outcome measures

The measurement techniques and selected outcome parameters used for evaluating different scenarios critically influence study findings and interpretations.

In hinge fracture analysis, differing criteria for risk assessment have contributed to inconsistencies in the literature. Numerical studies predominantly rely on strain- or stress-based metrics. Meisterhans et al. [23] used the ratio of mean principal strain in the hinge to the cortical bone's ultimate strain, arguing that strain-based failure better represents cortical behaviour and avoids peak stress artifacts. In contrast, Higa et al. [42] and Kuwashima et al. [40] used maximum shear and von Mises stress, respectively, although stress-based approaches remain a question of debate since bone fracture is generally strain-governed [71, 72]. Experimental studies further diverge. Mereb et al. [7] defined fracture as $a \ge 40\%$ drop in opening force, identifying structural failure rather than initiation. This contrasts with numerical models, which typically reflect damage onset rather than fracture completion. A future study incorporating both crack initiation and propagation up to final failure could provide a more comprehensive understanding of hinge fracture behaviour.

In studies assessing stability following DFO, various techniques have been employed to quantify micromotion near the osteotomy site. Brinkman et al. [47] and Peez et al. [32] utilized motion tracking systems (Fig. 3b) to capture relative displacements across the osteotomy line during mechanical loading. Ogawa et al. [48] applied strain gauges to measure local strains in the hinge region and fixation plate, while

Matsushita et al. [31] combined both motion tracking and strain measurements to provide a more comprehensive assessment. Additionally, overall construct stiffness and peak force values recorded during loading tests were used as indirect indicators of stability in several studies [43, 47,48]. Although these approaches provide valuable insight into early postoperative stability, the relationship between these early stability metrics and long-term outcomes such as bone healing or fixation integrity remains unexplored.

To evaluate changes in knee joint loading following DFO, both cadaveric studies by Quirno et al. [56] and Wylie et al. [58] employed pressure-sensitive sensors inserted into the medial and lateral compartments to quantify mean contact pressure, peak contact pressure and contact area across different conditions. In contrast, Wu et al. [5] conducted a finite element analysis to assess stress distributions within the femoral cartilage and meniscus, using peak Von Mises stress as an indicator of potential cartilage damage and meniscal tears and shear stress as a proxy for the risk of cartilage degeneration. While their approach provides valuable insights into internal tissue loading, incorporating contact pressure (as used in the cadaveric studies [56,58]) could further enhance the comparability and clinical relevance of the numerical findings.

## 4. Conclusion and perspective

This review aims to synthesize the current biomechanical knowledge on distal femoral osteotomy based on experimental, numerical and observational studies published between 2010 and 2025. Overall, the literature demonstrates that hinge position, osteotomy configuration and fixation method are the main determinants of mechanical stability and postoperative outcomes. Placing the hinge within the condylar region markedly reduces the risk of cortical fracture and loss of correction, while an excessive hinge width increases fracture incidence. Bi-planar osteotomies improve cortical contact and favour faster and more reliable bone healing. Among fixation methods, angled blade plates provide the highest structural stiffness, although locking plates achieve comparable stability when combined with hinge screws or bone grafts. Correction toward a neutral or slightly varus mechanical axis optimizes load redistribution and minimizes the risk of medial overloading.

<footnote n="3">³ Reprinted from Mereb et al. (2023) with permission. Original source DOI: 10.1016/j.otsr.2022.103527</footnote>
<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Experimental setup and specimen placement used³ by Mereb et al. [7]. Reprinted from *Orthopaedics & Traumatology: Surgery & Research*, Vol 109, Issue 4, Mereb et al., "Experimental study of risk of medial hinge fracture during distal femoral varus osteotomy", Page 103527, Copyright (2023), with permission from Elsevier.</figcaption></figure>

Despite these advances, important limitations and gaps persist in the literature. The following sections summarize the practical implications of these results and outline key directions for future research.

## 4.1. Recommendations for surgical decision-making

The biomechanical insights synthesized in this review have several implications for preoperative planning, surgical execution and postoperative management of DFO.

- **Surgical planning and hinge positioning:** Finite element and cadaveric studies consistently show that hinge location is a critical determinant of both fracture risk and correction stability. Positioning the hinge within the condylar region rather than the supracondylar

cortex reduces the likelihood of cortical failure and loss of correction. Excessive hinge width (>10 mm) should be avoided to prevent abrupt tensile failure during opening or closing. In cases where higher correction angles are required, MCW-DGO presents lower risk of hinge fracture, compared to LOW-DFO.

- **Choice of osteotomy configuration:** Bi-planar osteotomies, although technically demanding, increase cortical contact area and enhance stability, facilitating faster bone union.

- **Fixation strategy:** Mechanical comparisons indicate that angle-blade plates still provide the highest structural stiffness, but locking plates achieve comparable stability when combined with supplemental hinge screws or bone grafts. Patient-specific factors should therefore guide fixation choice rather than a single standard. Bi-cortical hinge screws or short support plates can restore stiffness following intra- or postoperative hinge fracture.

- **Use of hinge protection and grafting:** Insertion of a Kirschner wire through the hinge can lower fracture incidence. Gap filling can provide additional load-sharing capacity and early mechanical support, but there is a lack of studies in this area.

- **Alignment goals and joint mechanics:** Experimental and numerical analyses demonstrate that correction to a neutral or mildly varus mechanical axis (0–2°) achieves balanced tibiofemoral load distribution while preventing medial overload. Overcorrection beyond this increases medial compartment stress and should be avoided. Surgeons should also consider the downstream effects on hip and ankle alignment; pre- and postoperative long-leg radiographs remain essential to evaluate these compensatory changes.

## 4.2. Limitations of the current literature

Current biomechanical studies on DFO present several methodological limitations:

- **Sample limitations:** Most experimental investigations use small sample size and elderly cadaveric specimens, which do not reflect the bone quality and physiology of the younger, active DFO population.

- **Simplified bone models:** Synthetic composite bones provide reproducible conditions but fail to capture the heterogeneity of bone density and the mechanical influence of soft tissues.

- **Material modelling assumptions:** Finite element analyses frequently treat bone as an isotropic, linearly elastic material, neglecting its anisotropic and viscoelastic properties and thereby reducing physiological accuracy.

- **Lack of standardization:** Definitions of hinge fracture risk vary widely. Numerical studies typically assess failure based on stress- or strain-based initiation criteria, whereas experimental works often define it according to complete fracture. Testing configurations, boundary conditions and loading protocols also differ across studies.

- **Absence of validation:** No studies have directly validated finite element predictions against in vivo measurements or clinical outcomes.

## 4.3. Gaps and future directions

There are still some areas that have not yet been investigated in the literature. Regarding the numerical models, interesting methods exist in other areas of biomechanics that could apply to DFO.

- **Lack of fracture modelling in finite element simulations:** Current finite element studies on hinge fractures in DFO typically assess only failure initiation and do not simulate the actual fracture process. Incorporating explicit fracture modelling (such as XFEM or cohesive zone modelling) would allow simulation of crack initiation, propagation and final failure, as previously demonstrated in the context of HTO by Saghaei and Hashemi [69].
- **Limited data on healing biomechanics:** No biomechanical studies have yet addressed the healing phase following DFO. Bone healing models available in the literature, such as those proposed by Engelhardt et al. [73] and Zaheer et al. [74], could be adapted to simulate callus formation and maturation within the osteotomy gap. Such modelling would enable investigation of the time-dependent mechanical behaviour and its effect on consolidation and correction maintenance.

- **Influence of rehabilitation protocols:** The biomechanical impact of different postoperative loading and rehabilitation strategies on bone healing remains unexplored. Combining experimental cyclic loading studies with computational healing models could help optimize rehabilitation protocols by identifying load progressions that promote bone regeneration without compromising fixation stability.

- **Influence of patient-specific factors such as bone quality:** influence of patient specific factors such as bone quality has not been considered specially in hinge fracture studies. A study is required with models with different cortical thicknesses and trabecular densities to assess the influence of such patient-specific factors.

- **Influence of gap filling material:** The biomechanical performance of various bone substitutes used to fill the osteotomy gap (such as autografts, allografts, or β-tricalcium phosphate) remains poorly characterized. Experimental or finite element studies using LOW-DFO configurations across different correction angles could assess how filler stiffness and interface mechanics affect stability and post-surgery failures.

## CRediT authorship contribution statement

**Sohrab Rezaei:** Writing – original draft, Visualization, Methodology, Investigation, Formal analysis, Conceptualization. **Massamaesso Bilasse:** Writing – review & editing, Validation, Supervision, Methodology. **Yamen Othmani:** Writing – review & editing, Validation, Supervision, Methodology. **Nadia Bahlouli:** Writing – review & editing, Supervision, Project administration. **Matthieu Ehlinger:** Writing – review & editing, Supervision, Project administration, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgments

The authors express their gratitude to Professor Paul Montgomery for his guidance regarding the scientific writing and language of this manuscript. Furthermore, we acknowledge the funding and support received from Icam, Site de Strasbourg and ITI HealthTech, University of Strasbourg for this research project. This work of the Interdisciplinary Thematic Institute HealthTech, as part of the ITI 2021–2028 program of the University of Strasbourg, CNRS and Inserm, was supported by IdEx Unistra (ANR10-IDEX-0002) and SFRI (STRAT'US project, ANR-20-SFRI-0012) under the framework of the French Investments for the Future Program.

## Supplementary materials

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.nexres.2025.101207.

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