A pilot hole does not reduce the strains or risk of fracture to the lateral cortex during and following a medial opening wedge high tibial osteotomy in cadaveric specimens

Finite Element Analysis of Protective Measures against Lateral Hinge Fractures in High-Tibial Osteotomy

Background

Opening wedge high-tibial osteotomy (OWHTO) is widely used for correcting mechanical axis deviations and offloading the medial compartment in unicompartmental osteoarthritis. However, lateral hinge fractures (LHFs) pose a significant complication. This study investigates protective measures to mitigate these fractures, guided by prior observations of mechanical stress impact on LHFs.

Purpose

The study aims to assess the effectiveness of different protective measures, specifically the use of varying sizes of Kirchner wires and drill holes, in reducing the incidence of LHFs during OWHTO. Study Design. The study employs a quantitative, comparative analysis using a finite element method (FEM) based on computed tomography (CT) scans.

Methods

Using CT-based FEM, the study compares the impact of different sizes of K-wires (1.6 mm, 2.0 mm, and 2.5 mm) and drill holes (3.2 mm and 4.5 mm) on the mechanical stresses around the hinge area in OWHTO. The models were created from a CT scan of a healthy 33-year-old male, focusing on the force required to open the osteotomy gap and the incidence of cracked shell elements.

Results

The study found that thicker K-wires increased the force required to open the osteotomy gap, whereas larger apical holes decreased it. The 4.5 mm apical hole model demonstrated significantly fewer cracks compared to the 2.0 mm K-wire model, with no significant difference observed compared to the 2.5 mm K-wire model. Models using a 1.6 mm K-wire or a 3.2 mm drill hole did not significantly reduce cracks compared to the base model.

Conclusions

The findings suggest that a 4.5 mm drill hole may be more effective in reducing the risk of LHFs compared to thinner diameter K-wires or smaller apical holes. Both a 2.5 mm K-wire and a 4.5 mm drill hole reduce the number of cracked elements, but the 4.5 mm drill hole also significantly decreases the average and maximum principal stresses as well as the average tensile strength ratio at the hinge area. These findings may be important for surgical planning, particularly in cases requiring increased osteotomy distraction.

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.

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 location and apical drill holes in opening wedge high tibial osteotomy: A finite element analysis

At the time of medial opening wedge high tibial osteotomy (HTO) to realign the lower limb and offload medial compartment knee osteoarthritis, unwanted fractures can propagate from the osteotomy apex. The aim of this study was to use finite element (FE) analysis to determine the effect of hinge location and apical drill holes on cortical stresses and strains in HTO. A monoplanar medial opening wedge HTO was created above the tibial tuberosity in a composite tibia. Using the FE method, intact lateral hinges of different widths were considered (5, 7.5, and 10 mm). Additional apical drill holes (2, 4, and 6 mm diameters) were then incorporated into the 10 mm hinge model. The primary outcome measure was the maximum principal strain in the cortical bone surrounding the hinge axis. Secondary outcomes included the force required for osteotomy opening, minimum principal strain, and mean cortical bone stresses (maximum principal/minimum principal/von Mises). Larger intact hinges (10 mm) were associated with higher cortical bone maximum principal strain and stress, lower minimum principal strain/stress, and required greater force to open. Lateral cortex strain concentrations were present in all scenarios, but extended to the joint surface with the 10 mm hinge. Apical drill holes reduced the mean cortical bone maximum principal strain adjacent to the hinge axis: 2 mm hole 6% reduction; 4 mm 35% reduction; and 6 mm 55% reduction. Incorporating a 4-mm apical drill hole centered 10 mm from the intact lateral cortex maintains a cortical bone hinge, minimizes cortical bone strains and reduces the force required to open the HTO; thus improving control.

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.

A synthetic bone insert may protect the lateral cortex and fixation plate following a high tibial osteotomy by reducing the tensile strains

PURPOSE

To determine the effectiveness of a synthetic bone insert on improving medial opening wedge high tibial osteotomy integrity in response to post-surgical cyclical loading.

MATERIALS AND METHODS

A medial opening wedge high tibial osteotomy, secured with a compression fixation plate, was performed on 12 cadaveric knee specimens that were randomised to either: (1) a synthetic insert condition (n = 6), in which a 9 mm bio-absorbable wedge was inserted into the gap space; or (2) a plate-only condition (n = 6). Uniaxial strain gauges, placed on the lateral cortex and fixation plate, measured the strain response as the specimens were subjected to a staircase cyclical loading protocol; a sinusoidal waveform between 100 and 800 N was applied and increased by increments of 200 N every 5000 cycles until failure. Peak strains at failure were compared between conditions using a one-tailed independent samples t test.

RESULTS

The strains from the fixation plate were significantly different between the insert and plate only conditions (p = 0.02), transitioning from a compressive strain with the wedge (mean [SD] = - 8.6 [- 3.6] µε) to a tensile strain without the wedge (mean [SD] = 12.9 [23] µε). The strains measured at the lateral cortex were also significantly affected by the inclusion of a synthetic bone insert (p = 0.016), increasing from - 55.6 (- 54.3) µε when the insert was utilised to 23.7 (55.7) µε when only the plate was used.

CONCLUSIONS

The addition of a synthetic insert limited the tensile strains at the plate and lateral cortex, suggesting that this may protect these regions from fracture during prolonged loading.

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.

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.

Development and validation of a finite element model to simulate the opening of a medial opening wedge high tibial osteotomy

Medial opening wedge high tibial osteotomy (MOWHTO) is a surgical procedure intended to alter the coronal and sagittal plane alignment of the lower limb to primarily relieve the symptoms of osteoarthritis in the medial compartment of the knee. The purpose of this work was to develop and validate a finite element model to simulate the opening of a high tibial osteotomy and determine whether a pilot hole at the cortical hinge reduces the risk of lateral cortical fracture. Fifteen models were reconstructed from CT images of eight cadaveric specimens. The validated models indicated that the addition of the pilot hole increased the stresses and likelihood of a type-I and type-II fractures during the opening of a medial open wedge high tibial osteotomy compared to the no-hole condition.

Editorial Commentary: Lateral Hinge Fracture in High Tibial Osteotomy: Risk or Annex?

The basic aim of the medial opening wedge high tibial osteotomy is to use the elasticity of the lateral cortex as a biomechanical stabilizer, whereas the medial opening gap is maintained by a locking plate. This surgical construct tolerates early weight bearing, free range of knee motion, and sufficient bone healing for an acceptable time. We always perform a biplanar osteotomy, which reduces risk of fracture and improves healing potential owing to more bony contact area. We take some time opening the wedge owing to the elasticity of the lateral cortex. Careless manipulation can harm your hinge! Preoperative planning regarding corrective and postoperative expected joint line angles is key. If the gap is more than 10 mm, we use autologous bone graft or substitute. Partial weight bearing is indicated for 6 weeks to reduce fracture risk. When indicated, we perform double osteotomies, at the distal femur and proximal tibia, to perfectly achieve postoperative joint angles within the intended mechanical axis goal. Fractures of the lateral hinge occur in up to 30% of cases, whereas our nonunion rate is 5.4%.