Mechanical strength assessment of a drilled hole in the contralateral cortex at the end of the open wedge for high tibial osteotomy

Optimal hinge level in opening wedge high tibial osteotomy: Biomechanical analysis using finite element method

BACKGROUND

While the concept of a safe zone, which can minimize the hinge fracture when performing opening wedge high tibial osteotomy, has been introduced, there is a lack of understanding of the biomechanical environment at the lateral tibial cortex. This study aimed to evaluate the effect of the hinge level on the biomechanical environment at the lateral cortex of the tibia with heterogeneous finite element models.

METHODS

Finite element models of biplanar opening wedge high tibial osteotomy based on computed tomography images of a control subject and three patients with medial compartment knee osteoarthritis were created. In each model, three different hinge levels (proximal, middle, and distal) were set. The process of opening the gap during the operation was simulated, and the maximum von Mises stress values at the lateral tibial cortex were calculated for each hinge level and correction angle.

FINDINGS

The maximum von Mises stress value at the lateral tibial cortex was the lowest when the hinge was at the middle, while the value was the highest when the hinge was at the distal level. Furthermore, it was demonstrated that a higher correction angle yielded a higher probability of lateral tibial cortex fracture.

INTERPRETATION

The findings of this study demonstrate that the hinge at the point where the upper end of the articular cartilage of the proximal tibiofibular joint is located provides the least possibility of lateral tibial cortex fracture, as this is an anatomically independent position from the fibula.

Homogeneous material models can overestimate stresses in high tibial osteotomy: A finite element analysis

Although widely used numerical models can assess the stability of lateral hinges in high tibial osteotomy (HTO) and may provide acceptable results in comparative studies, accurate stress prediction may not be possible due to simplified homogeneous models of the bone. The present study aimed to investigate the effect of a heterogeneous versus four homogeneous models on the results of stress and force. Each of the four homogenized FE models utilized the same elastic modulus of 16,700 MPa for the cortical while employing a single elastic modulus varying from 155 to 5000 MPa for the cancellous. In heterogeneous model, the modulus of each element was assigned using the bone density. It was found that stresses at the hinge in homogeneous models were higher than those in the heterogeneous model. The maximum principal stress (MPS) was 437 MPa for the heterogeneous model while that was 2179, 2351, 2581, and 2637 MPa for the homogeneous models with the elastic moduli of 155, 500, 2130, and 5000 MPa, respectively. Also, the opening force was 150 N for the heterogeneous model significantly lower than 649-1534 N range predicted for the homogeneous models. The use of a homogeneous model in the FE analysis of HTO overestimated the stresses and force. Thus, in addition to casting doubt on the use of a single modulus in the numerical analysis of HTO, Future HTO studies can use our results as a benchmark for comparison purposes and highlight the use of patient-specific bone density - elastic modulus relation in simulation.

Experimental investigation of the risk of lateral cortex fracture during valgus tibial osteotomy

BACKGROUND

Valgus-producing medial opening-wedge proximal tibial osteotomies (V-MOW-PTO) are used to treat isolated medial-compartment knee osteoarthritis in patients with varus malalignment. A fracture of the lateral cortical hinge is a risk factor for poor outcomes. Implantation of a protective K-wire has been suggested to prevent this complication. The primary objective of this bench study was to assess the ability of a protective K-wire to prevent lateral cortical fractures. The secondary objective was to evaluate the influence of the opening speed on fracture risk during the osteotomy.

HYPOTHESIS

The primary hypothesis was that a protective K-wire decreased the risk of hinge fracture. The secondary hypothesis was that this risk was greater when the opening speed was high.

MATERIALS AND METHODS

We performed an experimental study of 20 simulated thermoplastic-polymer (ABS) tibias obtained by 3D printing to assess the effects of wedge-opening speed (high vs. low) and presence of a protective K-wire (yes vs. no). The opening rates were determined in a preliminary study of Sawbone® specimens opened using a distractor. The opening rate was measured using an accelerometer via a motion-capture glove. After assessing several high and low opening speeds, we selected 38mm/min and 152mm/min for the study. We divided the 20 ABS specimens into four groups of five each: high speed and K-wire, low speed and K-wire, high speed and no K-wire, and low speed and no K-wire. The force was applied using an Instron™ testing machine until construct failure. The primary outcome measure was the load at failure (N) and the secondary outcome measures were the displacement (mm) and maximum time to failure (s).

RESULTS

At both speeds, values were significantly higher with vs. without a K-wire for load to failure (low: 253.3N vs. 175.5N, p<0.01; high: 262.2N vs. 154.1N, p<0.01), displacement (low: 11.1mm vs. 8.7mm, p<0.01; high: 11mm vs. 8.9mm; p=0.012), and maximal time to failure (low: 11.4 s vs. 8.9 s; p=0.012; high: 2.2 s vs. 1.8 s; p=0.011). Thus, the osteotomy opening speed seemed to have no influence on the risk of lateral cortex fracture.

DISCUSSION

Our main hypothesis was confirmed but our secondary hypothesis was refuted: a protective K-wire significantly decreased the risk of hinge fracture, whereas the osteotomy opening speed had no influence. To our knowledge, this is the first published study assessing the potential influence of opening speed on risk of lateral cortex fracture. Our findings were obtained in the laboratory and should be evaluated in clinical practice.

LEVEL OF EVIDENCE

IV, experimental study.

Hinge fractures reaching the tibial plateau can be caused by forcible opening of insufficient posterior osteotomy during open-wedge high tibial osteotomy

PURPOSE

The purpose of this study was to use the finite element method (FEM) to reproduce fracture lines that reach the lateral tibial plateau during open-wedge high tibial osteotomy (OWHTO) in patients with Type III lateral hinge fracture (LHF). It was hypothesized that the FEM could clarify biomechanical causes of Type III LHF, enabling prevention of adverse complications.

METHODS

This study used the nonlinear FEM to analyze the data of eight knees in eight patients (two males and six females) with Type III LHF among 82 patients who underwent OWHTO, as well as the data of eight individuals with no LHF. To predict the onset of Type III LHF, simulation models were also developed in which posterior osteotomy sufficiency varied from 50% to perfect, the latter defined as osteotomy reaching the hinge point.

RESULTS

Real-life instances of Type III LHF caused by insufficient posterior osteotomy were reproduced in all patient-specific FEM models, and these models accurately predicted fracture types and locations. During opening of the osteotomy gap, the fracture line reached the lateral tibial plateau, and extended vertically from the end of the insufficient posterior osteotomy, avoiding the rigid proximal tibiofibular joint. In contrast, sufficient posterior osteotomy resulted in a lack of LHF. Posterior osteotomy extension ≥ 70% of the width of the osteotomy plane was the cut-off value to prevent Type III LHF.

CONCLUSION

Forced opening of insufficient posterior osteotomy was found to be a biomechanical cause of Type III LHF that extended perpendicularly to the lateral tibial plateau, avoiding the proximal tibiofibular joint. The clinical significance of this study is that sufficient posterior osteotomy during OWHTO, defined as at least 70% of the width of the osteotomy plane, can prevent Type III LHF.

Orientation and end zone of the osteotomy cut for high tibial osteotomy: Influence on the risk of lateral hinge fracture. A finite element analysis

INTRODUCTION

the hinge plays a fundamental role in the support and consolidation of a high tibial osteotomy. The objective of this work was to analyse the influence of the end zone of the osteotomy cut and its orientation in relation to the articular joint line (JL) on the risk of hinge fracture.

HYPOTHESIS

a specific orientation and end zone of the osteotomy cut can be utilised to decrease the risk of hinge fracture.

MATERIAL AND METHOD

a finite element (FE) model was used to reproduce the proximal portion of the tibia and the proximal tibiofibular joint with transverse isotropic elastic bone properties. A 1.27mm thick, complete, anteroposterior saw cut was made with a U-shaped saw blade. Five proximal and lateral tibial zones were used according to Nakamura et al corresponding to the end zones of the osteotomy cut. Three angulations of the cut relative to the JL were defined: 10°, 15°, 20°. The tests consisted of simulating 15 possible situations (3 angulations for each of the 5 end zones) on this model. These simulations made it possible to identify the existence of a local stress concentration (von Mises, in MPa) at the level of the hinge, corresponding to the main judgment criterion.

RESULTS

If we consider only the end zones of the osteotomy cut, regardless of its angulation with respect to the JL, the zone which presents, on average, the lowest local stress concentration is the AM zone (40.3MPa). If we consider only the angulation of the osteotomy cut, with respect to the JL, regardless of the end zone of the cut, the angulation that locally concentrates, on average, the least stress is an angulation at 10° (147.7MPa). Finally, it is important to define the best end zone of the osteotomy cut for each angulation value in relation to the JL: for an angulation of 10°, the end zone must be in AM (38MPa), but also for an angulation of 15° (45MPa), and for an angulation of 20° (38MPa).

DISCUSSION-CONCLUSION

With the inherent caveats of the experimental conditions, the hypothesis is confirmed. An end zone of the osteotomy cut exists (AM) and an orientation (10°) that induces the lowest local stress concentration and therefore the least likely to induce lateral hinge fracture. However, the orientation of the osteotomy cut is also a matter of surgical habit, especially regarding complementary osteotomy of the tibial tuberosity that some may want to avoid. Thus, it is equally important to know the best end zone associated with a given angulation of the cut in relation to the JL, which according to these results is the AM zone for each angulation. This information helps guide the operator in their surgical practices according to their habits.

LEVEL OF EVIDENCE

V, expert opinion.

Effect of hinge length on the lateral cortex fracture in high tibia osteotomy: an XFEM study

The main disadvantage of high tibial osteotomy (HTO) is the fracture of the lateral hinge during surgery. Therefore, the present study was designed to investigate the effect of different hinge lengths on the fracture type of the lateral hinge during the opening in HTO. For this purpose, extended finite element method (XFEM) was used to predict the crack initiation and growth in bone cortex in twelve models, each with different hinge lengths and medial start points. It was shown that extending the hinge length from 5 to 10, 16 and 22 mm increased the maximum principal stress around the hinge, and thus the fracture probability. A minimal effect on the results was observed by changing medial starting point of the cut from 30 to 35 and 40 mm. As a result, the extended finite element analyses confirmed the hypothesis that the extension of hinge segment increases the likelihood of a type II and type III fractures.

A supplemental screw enhances the biomechanical stability in medial open-wedge high tibial osteotomy

Background

The supplemental screw technique was introduced for salvage of lateral hinge fracture in medial open-wedge high tibial osteotomy (owHTO). The efficacy of its use in protection of lateral hinge fracture and corresponding biomechanical behaviors remained unclear. The current study was aimed to clarify if a supplemental screw can provide better protection to lateral hinge in biomechanical perspective.

Materials

An in vitro biomechanical test was conducted. Tibial sawbones, commercial owHTO plates and a cannulated screw were utilized for preparing the intact, owHTO, and owHTO with cannulated screw insertion specimens. A “staircase” dynamic load protocol was adopted for axial compressive test with increasing load levels to determine structural strength and durability by using a material testing system, while a motion capture system was applied for determining the dynamic changes in varus angle and posterior slope of the tibia plateau with various specimen preparation conditions.

Results

Type II lateral hinge fracture were the major failure pattern in all specimens prepared with owHTO. The insertion of a supplemental cannulated screw in medial owHTO specimens reinforced structural stability and durability in dynamic cyclic loading tests: the compressive stiffness increased to 58.9–62.2% of an intact specimen, whereas the owHTO specimens provided only 23.7–29.2% of stiffness of an intact specimen. In view of tibial plateau alignment, the insertion of a supplemental screw improved the structural deficiency caused by owHTO, and reduced the posterior slope increase and excessive varus deformity by 81.8% and 83.2%, respectively.

Conclusion

The current study revealed that supplemental screw insertion is a simple and effective technique to improve the structural stability and durability in medial owHTO.

A protective hinge wire, intersecting the osteotomy plane, can reduce the occurrence of perioperative hinge fractures in medial opening wedge osteotomy

PURPOSE

A recent study reported that positioning a K-wire to intersect the cutting plane at the theoretical lateral hinge location increases the lateral hinge's resistance to fracture during the opening of opening wedge high tibial osteotomy (OWHTO). The purpose of this study was to evaluate the clinical relevance of the use of this K-wire and its benefits in terms of lateral hinge protection during OWHTO in daily practice.

METHODS

A retrospective comparative study identified 206 patients who underwent OWHTO from January 2014 to December 2017. Among these patients, 71 had an additional K-wire (HK + group), whereas 135 did not (HK- group). The subjects meeting the inclusion criteria were included in a matched pairing process, which identified 60 patients in the HK + group and 60 patients in the HK- group. Mean follow-up time was 2.3 ± 1.0 years (range 2-4.2). Radiographic outcomes were evaluated with intraoperative and postoperative fluoroscopic imaging and with CT imaging at 6 weeks post OWHTO surgery. The knee osteoarthritis outcomes score (KOOS) was used and time needed to return to work and any kind of sports was collected.

RESULTS

Thirty six patients (30%) were found to have a LHF. Among these patients, 26 (72%) did not have an additional K-wire positioned at their theoretical lateral hinge location (HK- group) during the procedure. LHF rate for patients without additional K-wire group (HK-) was 43.3%, whereas it was 16.7% for the patients with an additional K-wire (HK +) [Odd ratio 3.8 95% CI 1.6-8.3; p = 0.005]. The mean time to return to work, return to any kind of sports, and bone union was significantly shorter for HK + group (p < 0.05).

CONCLUSION

This study demonstrated that during OWHTO, positioning a K-wire intersecting the cutting plane at the theoretical lateral hinge location reduced the number of intraoperative lateral hinge fractures.

LEVEL OF EVIDENCE

III retrospective case-control study.

Uniplane medial opening wedge high tibial osteotomy relative to a biplane osteotomy can reduce the incidence of lateral-hinge fracture

PURPOSE

With surgical modifications reflecting plate design differences of the specific rigid locking plate adding a metal wedge, uniplane high tibial osteotomy (HTO) has fewer lateral-hinge fractures and fewer plate irritations than biplane HTO.

METHODS

Uniplane HTO with a rigid locking plate adding a metal wedge was compared with biplane HTO with a rigid locking plate including a proximal D-hole. For comparison, the HTO patients' medical records and radiological results in a single institution were retrospectively reviewed. The Oxford knee score 2 years post-operation, CT scan at post-operative day 2 and serial standing long-bone scanography were reviewed to evaluate clinical outcome and radiological results, including the incidence of lateral-hinge fracture, plate irritation and correction loss to varus alignment.

RESULTS

A total of 103 knees, including 59 uniplane HTO and 44 biplane HTO, were enrolled. The Oxford scores were 38.1 ± 7.8 in the uniplane group and 35.9 ± 8.3 in the biplane group (ns). On CT scans, more lateral-hinge fractures developed in the biplane group, and seven knees (12%) of the uniplane group and 12 knees (27%) of the biplane group had Takeuchi type I stable hinge fracture (p < 0.05); unstable fracture was not noted in either group. Plate irritation occurred in nine knees (19%) of the uniplane group and in 14 knees (32%) of the biplane group, and the difference was statistically significant (p < 0.05).

CONCLUSION

In clinical situations including the use of surgical modifications reflecting plate design differences, fewer lateral-hinge fractures developed after uniplane medial opening-wedge HTO compared with biplane HTO. Uniplane HTO potentially represents a better option than biplane HTO for the prevention of lateral-hinge fracture.

LEVEL OF EVIDENCE

IV.

Adding a protective screw improves hinge's axial and torsional stability in High Tibial Osteotomy

BACKGROUNDS

Despite the use of a locking plate a 30% incidence of lateral hinge fracture after Open-Wedge High Tibial Ostetomy was described in the literature. A finite element model was used to analyze if the presence of a hinge-securing screw in the osteotomy area, using Patient Specific Cutting Guides with a locking plate, decreases the stresses within the lateral hinge during compression and torsion.

METHODS

A 3D model of a tibial sawbone was used to simulate an opening wedge of 10°. To apply loads on the tibial plateau, two supports were modelled on each tibial plateau to simulate the femoral condyles forces. A two second model with a hinge-stabilizing was defined with two different screws (diameter 2 mm and 4 mm). Two cases of static charges were considered 1) compression test (2500 N) 2) Torsion test (along the tibial mechanical axis).

FINDINGS

During compression simulation, 17% of the total surface of lateral hinge was stressed between 41-50Mpa without hinge-securing screw while the amount of surface under stress between 41 and 50 MPa dropped significantly under screw stabilization (1% for the 2 mm and 3% for the 4 mm). During torsion stress simulation a decrease of the value of the maximal stress in the lateral hinge was also observed with the addition of a hinge-securing screw (37 MPa without screw, 27Mpa with a 2 mm screw and 25 Mpa with a 4 mm screw).

INTERPRETATION

Positioning a screw intersecting the cutting plane at the theoretical lateral hinge location associated with a locking plate reduces lateral hinge stress in both compression and torsion. Those findings need to be confirmed by further specimens' mechanical testing.

Adding a protective K-wire during opening high tibial osteotomy increases lateral hinge resistance to fracture

PURPOSE

It was hypothesized in this in-vitro study that positioning a K-wire intersecting the cutting plane at the theoretical lateral hinge location would limit the cut depth and help preserve the lateral hinge during the opening of the osteotomy. Objectives were (1) to compare the mechanical resistance of the hinge and the protective effect of leaving the K-wire during the opening procedure (2) to check if the K-wire would limit the depth of the osteotomy.

METHODS

An ex-vivo mechanical study, testing 5 pairs of fresh-frozen tibias, was designed. CT-scan based Patient-specific cutting guides were obtained to define the cutting plane and the location of the K-wire at the hinge, using standardized 3D planning protocol. In each pair, OWHTO was performed either with or without the K-wire. To evaluate the hinge's resistance to fracture, the specimens were rigidly fixed at the proximal tibia and a direct load was applied on the free tibial diaphysis to open the osteotomy. The maximum load at breakage, maximum permissible displacement and maximal angulation of the osteotomy before hinge failure was measured. To assess the preservation of an unscathed hinge (protected by the K-wire), the distance from the end of the osteotomy cut to the lateral tibial cortical was measured in mm.

RESULTS

The maximum load to hinge breakage in the K-wires PsCG knees compared to the control group (48.3 N vs 5.5 N, p = 0.004), the maximum permissible displacement (19.8 mm vs 7.5 mm, p = 0.005) and the maximal angulation of the osteotomy before hinge breakage (9.9° vs 2.9°, p = 0.002) were all statistically superior in the K-wires PsCG knees compared to the control group. A mean distance of 10 ± 1 mm between cut-bone (saw-print) and lateral hinge cortical bone was found post-performing the osteotomy and the hinge failing.

CONCLUSION

The maximum load to breakage and the maximum permissible displacement were, respectively, 880% and 260% higher during the opening of the OWHTO in using K-wires compared to the non-K-wire control group. This confirms the mechanical advantage of using a K-wire for both stabilization and protecting the Hinge during OWHTO. This comparative cadaveric study shows an improvement of the lateral hinges resistance to failing during the opening of the osteotomy. This can be achieved by the placement of a K-wire intersecting the cutting plane at the theoretical location of the lateral hinge.

Effect of saw blade geometry on crack initiation and propagation on the lateral cortical hinge for HTO: Finite element analysis

INTRODUCTION

The hinge plays a primary role in the hold and healing of a high tibial osteotomy (HTO). Weakening of the hinge is a risk factor for failure. The aim of our study was to determine whether the geometry of the saw blade's cutting edge impacts crack initiation or propagation on the hinge.

HYPOTHESIS

A certain cutting edge geometry exists that will reduce this risk.

MATERIALS AND METHODS

A finite element model with transverse isotropic elastic bone properties was created. A 1.27-mm thick saw cut (full thickness in anteroposterior direction) was made leaving a 1cm lateral cortical hinge. Three different cutting edge geometries were compared: rectangular, U-shaped, V-shaped. Opening of the osteotomy was done over 1mm for 1 s by a load applied distally with the proximal portion fixed. In the first simulation, no crack was initiated at the hinge, while in the second simulation, the beginnings of a 2mm crack angled upward at 15° was added. These two simulations were used to identify whether a local stress riser was present at the hinge. This information was used to calculate the energy release rate to the hinge, which corresponds to the energy needed to initiate and propagate a crack on the hinge.

RESULTS

In the first simulation (no crack initiation), a rectangular saw blade geometry resulted in the lowest local stress concentration. In the second simulation (with crack initiation), the U-shaped geometry resulted in the lowest local stress concentration. The U-shaped geometry had the lowest energy release rate, meaning that it was the least likely to initiate and propagate a crack on the lateral cortical hinge.

DISCUSSION/CONCLUSION

Keeping the inherent limitations related to computer modelling in mind, our findings show that a U-shaped cutting edge is least likely to initiate or propagate a crack since it has the lowest energy release rate. This confirms our hypothesis.

LEVEL OF EVIDENCE

V, expert opinion.

High Tibial Osteotomy: Review of Techniques and Biomechanics

High tibial osteotomy becomes increasingly important in the treatment of cartilage damage or osteoarthritis of the medial compartment with concurrent varus deformity. HTO produces a postoperative valgus limb alignment with shifting the load-bearing axis of the lower limb laterally. However, maximizing procedural success and postoperative knee function still possess many difficulties. The key to improve the postoperative satisfaction and long-term survival is the understanding of the vital biomechanics of HTO in essence. This review article discussed the alignment principles, surgical technique, and fixation plate of HTO as well as the postoperative gait, musculoskeletal dynamics, and contact mechanics of the knee joint. We aimed to highlight the recent findings and progresses on the biomechanics of HTO. The biomechanical studies on HTO are still insufficient in the areas of gait analysis, joint kinematics, and joint contact mechanics. Combining musculoskeletal dynamics modelling and finite element analysis will help comprehensively understand in vivo patient-specific biomechanics after HTO.

[Study on lateral hinge fracture during open wedge high tibial osteotomy]

Objective

To summarize the related research results of open wedge high tibial osteotomy (OWHTO) complicated with lateral hinge fracture.

Methods

To review the relevant literature of OWHTO at home and abroad in recent years and summarize and analyse the clinical experience.

Results

The lateral hinge rupture may occur during the OWHTO, which may lead to the loss of correction angle after operation, delayed healing or non-union of osteotomy and so on. The lateral hinge plays an important role in the stability of the osteotomy. During the operation, the "safe zone" internal osteotomy can be used to protect the bone. Once the lateral hinge breaks, the TomoFix plate can be used to obtain the sufficient stability. For patients with lateral hinge rupture, functional exercise and full weight loading time should be guided by hinge breakage classification.

Conclusion

The intact lateral hinge is beneficial to the healing and rehabilitation of OWHTO. The lateral hinge should be paid enough attention by clinicians.