Abstract
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Lateral hinge fractures (LHF) are one of the most common complications of medial opening wedge high tibial osteotomy (MOWHTO), and are the leading cause of construct instability displacement, non-union, and varus recurrence after this procedure.
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To date, Takeuchi’s classification is the most popular classification to describe this complication, and it can help surgeons to make intra and postoperative decisions.
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Opening medial gap width is the most recognized factor related to LHF occurrence.
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Recognizing the implications of LHF in patients’ clinical and radiographic results has led many authors to propose surgical tips and the use of osteosynthesis materials such as K-wires and screws for its prevention, which should be considered when identifying risk factors for LHF during preoperative planning.
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The evidence for determining the optimal management of LHF is scarce and mostly supported by experts’ opinions and recommendations; therefore, studies are still needed to identify the most appropriate behavior when dealing with such a complication.
Introduction
Medial opening wedge high tibial osteotomy (MOWHTO) is a surgical procedure accepted as a treatment for medial compartment osteoarthritis in patients with knee varus malalignment, among other indications (1, 2, 3). Advantages of this surgery have been noted in comparison with the closing wedge high tibial osteotomy, such as minimizing the risk of common peroneal nerve injury (4, 5, 6). Nevertheless, as with any other surgical procedure, complications reported after MOWHTO are as high as 41.2%, with 24.7% of them being major complications (defined as complications that require additional or extended treatment) (7). Common major complications of MOWHTO are implant failure (8.2%), intraoperative lateral hinge fracture (LHF) (type II or III) (5.9%), distal locking screw breakage (4.7%), proximal locking screw breakage (3.5%), and superficial infection (2.4%), as listed by Yabuchi et al. (7).
LHFs are one of the most common complications of MOWHTO (8, 9, 10) and are the leading cause of construct instability, displacement, non-union, and varus recurrence after MOWHTO (2, 11, 12, 13, 14). Various risk factors have been described recently such as the location of the osteotomy, hinge position, and the osteotomy width (15). The purpose of this article is to outline LHF characteristics, its prevention methods, and management.
Epidemiology and diagnosis
LHF reported incidence varies between 3 and 30%, mostly based on radiographic reports (2, 16, 17, 18, 19, 20, 21). Fractures may occur intraoperatively or during the postoperative period, with reported incidence rates up to 18 and 14%, respectively (2, 5, 16, 18, 22, 23).
Intraoperative fluoroscopy or immediate postoperative radiographs may underestimate the rate of occurrence of LHF (9, 24). Thus, multiple studies recommend the use of computed tomography (CT) as the gold standard to detect occult LHF because of the significant increase in detection rate compared to plain radiographs (8, 9, 10, 24, 25, 26).
In 2018, Lee et al. reported a significant increase in LHF detection rate by using CT scans compared with plain radiographs, 50 vs 14.6%, respectively (95% CI, P < 0.001). To date, this study has reported the greatest incidence of recognition of LHF (24).
In a systematic review published by Kim et al. in 2021, the estimated incidence of LHF using CT scans was increased by 9.9% in contrast to plain radiographs alone (25). This review reported that as many as 40% of LHF may not be diagnosed with intraoperative fluoroscopy or postoperative radiographs. The authors suggest CT evaluation in patients with consistent lateral pain at rest, intraoperative fluoroscopy or postoperative radiographs with suspected LHF, and if more than a 11.4 mm opening gap was performed.
To date, to the best of our knowledge, there are no studies that compare LHF detection rates between magnetic resonance imaging (MRI) and other modalities. Suh et al. (27) used MRI to evaluate the occurrence of LHF, detecting fractures in 25% of their patients.
Classifications
The first LHF classification was proposed in 2012 by Takeuchi et al. (2), differentiating them into three different types. Type I fractures extend throughout the osteotomy line and continue through the lateral cortex proximal or at the same level as the proximal tibiofibular joint. Type II fractures extend distal to the proximal tibiofibular joint. In type III fractures, the fracture line extends into the lateral tibial plateau (Fig. 1).
Takeuchi´s Classification. Left: Type I fractures extend throughout the osteotomy line and continue through the lateral cortex proximal or at the same level as the proximal tibiofibular joint. Right: Type II fractures extend distal to the proximal tibiofibular joint and Type III fractures extends into the lateral tibial plateau..
Citation: EFORT Open Reviews 8, 7; 10.1530/EOR-22-0103
A recent biomechanical study conducted by Kang et al. (28) utilizing a finite element model of the knee, demonstrated that Takeuchi type I LHF had similar stability as a MOWTHO with intact lateral hinge. The study reported that Takeuchi types II and III LHF were unstable fracture patterns.
Clinical studies (21, 29, 30) agree with the unstable behavior of LHF types II and III, as reported by Nakamura et al., who described increased rates of delayed union, loss of correction, and overcorrection in comparison with type I LHF (17).
The Takeuchi classification allows the surgeon to properly characterize the fracture pattern and stability. However, it does not consider the fracture displacement. Dorofeev et al. proposed a modification to Takeuchi’s original classification (31), by further subclassifying LHF in types A (non-displaced), B (with displacement >2 mm evident on first detection), and C (LHF not displaced in the first detection, but with displacement >2 mm in subsequent controls). In their retrospective study, the rates of non-union were significantly higher in patients who presented LHF (15.4 vs 1.8%). In this study, 76.9% of the LHF corresponded to Takeuchi’s type I, and it was precisely this group that presented the highest rate of non-union (20%). This was probably due to the fact that the general management of type I fractures is less cautious compared to types II and III; however, the author does not specify in the study the management for these fractures. In their regression analysis, they highlighted the association between the degree of displacement and tibial non-union, with this parameter being more relevant than the specific type of fracture (31).
Predictive factors
Multiple factors have been described in order to determine their correlation with LHF occurrence. Age (8, 10, 17, 21, 24, 25, 26, 29, 30, 32, 34, 35), body mass index (BMI) (8, 10, 17, 21, 24-26, 29, 30, 32, 34, 35), hip–knee–ankle angle (8, 21, 24, 25, 29, 35), fibular position (26, 33, 35), tibial plateau width (33, 35), osteotomy’s position (21, 26, 29, 32), the magnitude of medial opening aperture (8, 10, 17, 21, 24-26, 30, 32, 34, 35), anterior gap and posterior gap (10, 26, 35), sagittal and coronal slope (10, 26), biplanar osteotomy (30), and wedge-hinge relation (21, 26) have been studied as contributing factors. Although only the opening medial gap width has shown consistent statistical significance throughout the literature (8, 10, 17, 21, 24, 25, 26, 30, 32, 34, 35). In a recent article published by Lee et al., they established that the 11 mm cutoff for opening the medial gap had a sensitivity and specificity for LHF of 78.4 and 73.9%, respectively (26). Previous studies proposed a higher cutoff, varying between 11.4 and 12 mm (24, 25).
LHF consequences
LHF as a consequence of a MOWHTO has been a matter of discussion in recent years and is considered a critical factor that can lead to delayed union, non-union, and loss of correction (2, 11, 12, 13, 14, 17, 29, 34, 36, 37, 38).
Delayed union and non-union are among the most feared complications of LHF (12, 16, 21, 39). The retrospective study conducted by Dorofeev et al. reported significantly higher non-union rates in patients with LHF (15.4 vs 1.8%), a fact that led to a greater rate of re-osteosynthesis (10.3% in this series) (31). Song et al. described a significantly greater time to union in patients with LHF (7.3 months) in contrast with the nonfracture group (5 months) (P < 0.001) (40). It has been stated that Takeuchi’s LHF type II had a higher risk of delayed union (41).
Osteotomy healing is not the only outcome affected by LHF, as fractures can alter the osteotomy correction precision and generate a sudden loss of correction on coronal alignment. Unstable fracture patterns, such as types II and III, or the presence of unnoticed complete osteotomies are considered risk factors that induce inadequate corrections. These unnoticed complete osteotomies may lead to imprecise correction even in type I stable patterns (29) since it is possible to lose the correction during the fixation of the osteotomy.
Loss of correction may alter the final tibial slope. Increases in tibial slope have been reported in patients with LHF and posterior cortex compromise. A 2.5° tibial slope change may be noticed as early as 3 weeks postoperatively in patients with LHF in comparison with 0.1° with the non-fractured posterior cortex (34).
Prevention
Recognizing the implications of LHF in the patients’ clinical and radiographic results has led many authors to propose guidelines and new technical strategies to prevent this complication (2, 21, 17, 32, 42).
Diverse technical considerations have been described to diminish the LHF occurrence risk (2, 32, 42, 43, 44, 45, 46, 47). Lobenhoffer and Agneskirchner (45) recommend the preservation of 10 mm between the osteotomy and the lateral cortex. To do that, the osteotomy is set to reach the proximal third of the tibiofibular joint without extending proximally. Takeuchi et al. (2) described that only 5 mm between the osteotomy and the lateral cortex is needed. Kessler et al. (46), in line with Lobbenhoffer and Agneskirchner, suggested 10 mm from the lateral cortex, in addition to a 20 mm bone bridge between the osteotomy and the lateral tibial plateau to minimize LHF risk.
Nakamura et al. (32) proposed a zone classification for hinge position, dividing osteotomies by their relation with the proximal tibio-fibular joint (PTFJ) and their depth in below (B), above shallow (AM), above deep (AL), within shallow (WM), and within deep (WL). The authors found that WL had a 0.24 relative risk of type II/III LHF, recommending this zone as the hinge-safe zone.
A significant association had been found between a sufficient osteotomy – a cut including the anterior and posterior cortex and ending at the same level as the tibiofibular joint (as defined by Ogawa et al.) – and LHF absence (21). Biplanar osteotomies have been introduced as a novel technique to reduce the risk of LHF (48) and may allow the surgeon to create a greater wedge gap. Nevertheless, recent literature has been published against this idea, stating that biplanar osteotomies lead to higher LHF rates than uniplanar osteotomies (30), which might reflect the real contribution of the soft tissues around the PTFJ, biomechanical properties of the proximal tibia, and the surgical differences implemented between both techniques is this study.
The use of a protective K-wire as a preventive measure for LHF has been popularized recently, with some clinical and biomechanical studies confirming its utility (50, 51). The K-wire is positioned intersecting the cutting plane at the theoretical location of the lateral hinge, acting as a mechanical restraint, and reducing the risk of lateral cortex fracture (Fig. 2) (50, 51). A cadaveric study conducted by Dessyn et al. demonstrated that a protective K-wire may increase load failure and maximum tolerable displacement up to 880 and 260%, respectively (50). Cannulated screws have also been used intending to increase MOWHTO structural stability (52, 53, 54). The screw is inserted from the lateral cortex with a 50-degree angle in the coronal plane and a 38.5-degree angle in the axial plane into the zone just below the lateral and medial tibial plateau (52). Contrarily to the K-wire technique, which is used to prevent intraoperative LHF, cannulated screws are placed to prevent secondary LHF; therefore, they are inserted after the ostetomy’s opening.
A K-wire is positioned intersecting the cutting plane at the theoretical location of the lateral hinge, acting as a mechanical restraint, and reducing the risk of lateral hinge fracture.
Citation: EFORT Open Reviews 8, 7; 10.1530/EOR-22-0103
Other strategies, like the insertion of bone graft substitutes and allografts have been proposed to increase stability (10, 55, 56). Van Genechten et al. (55) impacted a structural gap-filling bone allograft in their series, adding additional stability to the osteotomy site. In their prospective series, they reported a significant reduction in postoperative pain, early ambulation, and short-term clinical outcomes. Only one unstable LHF with non-union was listed in complications. However, systematic reviews and meta-analysis have failed to prove significant results regarding time to union, delayed union and nonunion (57, 58, 59). Contrarily, the incidence of LHF was noted to be lower when no bone filler was used (59).
Computer-assisted surgery may offer the surgeon a better control of the osteotomy’s depth. Saragaglia et al. have performed over 700 procedures between 2001 and 2015, obtaining more precise radiological outcomes (60). However, no significant differences have been found between navigated and conventional MOWHTO regarding clinical outcomes (61, 62), and no analysis has been made between the addition of navigation and the prevention of LHF.
Treatment
Stable fixation is required to assure a MOWHTO healing process. The presence of an LHF may affect the osteotomy’s outcome; thus, it becomes paramount to treat this complication if present. Yet, the evidence for determining the optimal management of LHF is scarce and mostly supported by experts’ opinions and recommendations.
Takeuchi et al. (2) suggest that according to the type of LHF, there may be differences regarding the osteotomy’s healing process, and the same was confirmed and developed by Nakamura et al. (17). Soft tissues adjacent to the proximal tibiofibular joint maintain the osteotomy’s stability in type I LHF, allowing a normal rehabilitation program under strict follow-up if early full weight-bearing is authorized. In type II LHF, the energy is absorbed by the fibula and transformed into rotational energy generating external rotation between the two fragments and contributing to the development of correction loss and non-union. A non-weight-bearing (NWB) rehabilitation program until a callus formation is evidenced on the osteotomy’s site is recommended. In type III LHF, the articular surface is damaged, as the fracture line exits through the lateral tibial plateau. The MOWHTO itself generates the passage of the axial load from the medial plateau to the lateral one, which is unfavorable in the presence of type III LHF. Takeuchi et al. (2) refer to type III LHF as a serious complication, but no clear recommendations are given to treat this particular type of LHF. On the other hand, Nakamura et al. (17) favors a modified rehabilitation protocol, in which partial weight-bearing is delayed for 3 weeks and full weight-bearing for 6 weeks. Additional fixation methods – lateral cannulated screws or locking plates – are only necessary if there is an articular surface displacement or loss of the osteotomy’s correction.
Conservative treatment of type I LHF with no weight-bearing restriction, as recommended by Takeuchi et al. (2), has been endorsed by several authors (20, 25, 63) when using long locking plates. Locking plates have been advocated to generate higher rotational and axial stability in comparison to conventional plates (13, 38, 49) and diminishing non-union rates (20, 50). A recent systematic review by Kim et al. (25) found no statistically significant clinical or radiographic differences between patients that suffered from LHF and those who did not. All patient groups included in this study were fixed with long locking plates, being TomoFix Anatomical Plate (Synthes, Oberdorf, Switzerland), the most frequently used.
A cautious acceptance of this recommendation is suggested as several of the series that propose unrestricted weight-bearing programs really apply partial weight-bearing in the initial stages. For instance, 7 of the 11 studies included in the systematic review by Kim et al. (25) reported initial restrictive rehabilitation programs for patients with LHF, irrespective of LHF type and emphasizing the weight-bearing restriction role in LHF management (8, 10, 21, 24, 32, 51, 64). The same authors reported in a previous study (63) good results for 16 type I and 21 type II LHF fixed with locked plate systems and a restrictive weight-bearing for 6 weeks. They described no correction loss or fracture union issues. Also, Lee et al. (10) observed a significant coronal alignment correction loss of type I LHF on their series while allowing full weight-bearing and, therefore, advised delaying weight-bearing regardless of the type of LHF.
Despite the positive results obtained from fixed locking systems and restrictive rehabilitation programs, these methods are not exempt from complications. Nakamura et al. (17) reported delayed union, loss of correction, and overcorrection in their case series of patients with unstable LHF type II and III, despite having used the TomoFix Plate and rehabilitation under a strict restrictive regime. Furthermore, a recent computational study (65) demonstrated that medial-locked plates do not grant sufficient stability for bone healing at the osteotomy and fracture line. An increment in medial plate’s tension due to LHF was found, elevating the risk of failure. The authors of this study recommended fixation with medial and lateral locked plates in the event of LHF, questioning the capacity of a medial plate to avoid displacement. However, this computational study has important limitations as the fibula was not included in the biomechanical model, therefore their conclusions could not reflect the in-vivo scenario.
In order to avoid complications, authors like Stannard and Kfuri advocate a prolonged NWB program and eventual fixation of type II LHF with a small-fragment lateral plate. For type III LHF, they recommend reduction and fixation with one or two lateromedial screws underneath the articular surface (66).
Author’s approach
We consider that the recognition of predictive factors is paramount in the preoperative planning of any MOWHTO. In cases when we plan medial openings greater than 11 mm, we consider a freehand placement of a protective K-wire guided by fluoroscopy which intersects in the cutting plane at the theoretical location of the lateral hinge, generating a mechanical stop of the oscillating saw and increasing load failure and maximum tolerable displacement. We consider that K-wires are a quick, economic, effective, and simple preventive LHF method. In all MOWHTO, we preserve at least 10 mm between the osteotomy and the lateral cortex regardless of the width of the medial opening.
We highlight the importance of an active search of LHF by using intraoperative fluoroscopy after the initial opening and also after fixation, regardless of the size of the opening gap. A postoperative radiographic control with anteroposterior and lateral projections of the knee is performed in all our patients. We perform monthly serial radiological follow-ups up to 4 months post-operative. As proposed by Kim et al. (25), we use further CT evaluation in patients with consistent lateral pain at rest, intraoperative fluoroscopy or postoperative radiographs with suspected LHF, and if a 11.4 mm opening gap was performed.
If an LHF is detected, we recommend classifying it by using the Takeuchi et al. classification (2), as it is not only descriptive but also guides treatment for LHF. In this fashion, our treatment modality for LHF varies considering two main variables: Takeuchi’s classification and time of fracture detection (intra or postoperative) (Fig. 3).
Author’s lateral hinge fracture management algorithm. LHF: lateral hinge fracture. WB: weight bearing. NWB: Non weight bearing.
Citation: EFORT Open Reviews 8, 7; 10.1530/EOR-22-0103
For intraoperative type I LHF, despite the results obtained by Chen et al. in their computational finite element model – with the limitations described earlier – (20), we consider that the fixation with a medial long locked plate is adequate, and we advocate partial weight-bearing during the initial 4–6 weeks of the rehabilitation period. If a type II or III LHF is evidenced during the surgical act, we prefer to add stability with a lateral anatomic plate or cannulated screws. Regarding the postoperative load, the initial NWB or partial weight-bearing protocol is determined by fracture site stability.
For postoperative type I LHF, we suggest a progressive partial weight-bearing protocol for 4 weeks. As for type II or III LHF identified postoperatively, we advocate for a 6-week partial weight-bearing period from fracture detection or until callus formation. If a >2mm displacement is identified postoperatively, considering the results obtained by Dorofeev et al. (31), we use a 4-week NWB protocol.
Irrespective of LHF type or time of detection, serial radiographic controls are maintained until the fracture is healed.
As a group, we advocate revision surgery in three scenarios. First, if correction loss is identified during follow-up. Second, in cases of established nonunion of the osteotomy site. And third, in displaced type III LHF with >5 mm of articular or condylar widening. It is important to add that to our knowledge, no evidence-based recommendations for revision surgery have been made in the literature.
Summary
LHFs are one of the most common complications of MOWHTO and the leading cause of displacement, non-union and varus recurrence. Due to the importance of its detection, the use of CT scan is recommended when there is suspicion for its diagnosis demonstrating a significant increase in detection rates compared to standard X-rays. Takeuchi´s classification is the most frequently used and it aids treatment decision-making, as stated by Nakamura et al. (17). The subclassification proposed by Dorofeev et al. (31) may assist decision treatment for postoperative LHF. Generally, type I LHF have been managed with partial load restrictions or early full weight bearing in the postoperative period. On the other hand, in LHF types II and III NWB regimes are indicated. Regardless of the type of fracture, prevention is always preferable to treatment. Knowing predisposing factors – such as making a medial opening > 11 mm – is essential. Applying prevention strategies such as preserving at least a 5–10 mm distance from the osteotomy to the lateral cortex, positioning the hinge in Nakamura’s WL safe zone (32), or the use of K-wires – while opening – or cannulated screws – after opening – may be good alternatives.
ICMJE conflict of interest statement
The authors declare that there is no conflict of interest that could be perceivedas prejudicing the impartiality of the research reported.
Funding
This study did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.
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