Biomechanical properties following open wedge high tibial osteotomy: Plate fixator combined with dynamic locking screws versus standard locking screws

Geometrical Planning of the Medial Opening Wedge High Tibial Osteotomy—An Experimental Approach

This article presents an experimental approach to the geometrical planning of the medial opening wedge high tibial osteotomy surgery which, as it is known, is an efficient surgical strategy quite widely used in treating knee osteoarthritis. While most of the published papers focus on analyzing this surgery from a medical point of view, we suggest a postoperative experimental evaluation of the intervention from a biomechanical point of view. The geometrical planning and, more specifically, the determination of the point of intersection between the corrected mechanical axis and the medial-lateral articular line of the knee, is a problem quite often debated in literature. This paper aims to experimentally investigate the behavior of the tibia with an open wedge osteotomy fixed with a locking plate, TomoFix (DE Puy Synthes), taking into account two positions of the mechanical axis of the leg on the width of the tibial plateau, measured from medial to lateral at 50% and 62.5% (Fujisawa point), respectively. The variations of the force relative to the deformation, strains, and displacements resulting from the progressive loading of the tibial plateau are studied. The research results reveal that using the Fujisawa point is better for conducting the correction not only for medical reasons, but also from a mechanical point of view.

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.

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.

Benefits of opposite screw insertion technique in medial open-wedge high tibial osteotomy: A virtual biomechanical study

Background

Alignment correction of the lower limb by medial open-wedge high tibial osteotomy (HTO) is an efficient technique, but loss of correction and hardware failure can occur owing to inadequate fixation. A surgical technique using opposite screw insertion was previously applied for salvage of the lateral hinge fracture, but evidence for its utility as a protective strategy was unclear.

Methods

Finite element models were reconstructed using artificial bone models, commercial bone plate, and locking screws in the HTO model. The 6.5-mm cancellous or 6.5/8.0-mm pretensioned lag screw was virtually inserted from the opposite cortex to the medial tibial plateau. Testing loads were applied for simulating standing and initial sit-to-stand postures. The axial displacement of the posteromedial tibial plateau, which represents the loss of the posteromedial tibial plateau in clinical observation, and stresses on the bone plate, locking screws, and opposite screws were evaluated.

Results

Pretensioned lag screw insertion effectively reduced the loss of posteromedial reduction compared with the HTO model without opposite screw insertion [6.5-mm lag screw, by 50.8% (standing)/56.3% (sit-to-stand); 8.0-mm lag screws, by 51.9% (standing)/57.5% (sit-to-stand); normalised by the performance in the intact model]. The noncompressed opposite cancellous screw slightly reduced the stresses on the bone plate and screws, but did not contribute to the control of reduction loss at the posteromedial tibial plateau. Stresses on screws were lower than those on the corresponding bone plates, so the risk of screw breakage may be low.

Conclusion

The present study revealed that pretensioned opposite lag screw insertion is a simple and effective technique to improve the structural stability in medial open-wedge HTO. Further biomechanical and clinical verification will be required to enhance user confidence in this technique.

The translational potential of this article

The efficacy and advantages of additional opposite lag screw insertion in medial wedge high tibial osteotomy surgery have been described in this current study by a virtual biomechanical evaluation. Basing on this observation, it would worth further clinical trials for clarification and verification in reality.