Assessing the Local Mechanical Environment in Medial Opening Wedge High Tibial Osteotomy Using Finite Element Analysis

Abstract

High-tibial osteotomy (HTO) is a surgical technique aimed at shifting load away from one tibiofemoral compartment, in order the reduce pain and progression of osteoarthritis (OA). Various implants have been designed to stabilize the osteotomy and previous studies have been focused on determining primary stability (a global measure) that these designs provide. It has been shown that the local mechanical environment, characterized by bone strains and segment micromotion, is important in understanding healing and these data are not currently available. Finite element (FE) modeling was utilized to assess the local mechanical environment provided by three different fixation plate designs: short plate with spacer, long plate with spacer and long plate without spacer. Image-based FE models of the knee were constructed from healthy individuals (N = 5) with normal knee alignment. An HTO gap was virtually added without changing the knee alignment and HTO implants were inserted. Subsequently, the local mechanical environment, defined by bone compressive strain and wedge micromotion, was assessed. Furthermore, implant stresses were calculated. Values were computed under vertical compression in zero-degree knee extension with loads set at 1 and 2 times the subject-specific body weight (1 BW, 2 BW). All studied HTO implant designs provide an environment for successful healing at 1 BW and 2 BW loading. Implant von Mises stresses (99th percentile) were below 60 MPa in all experiments, below the material yield strength and significantly lower in long spacer plates. Volume fraction of high compressive strain ( > 3000 microstrain) was below 5% in all experiments and no significant difference between implants was detected. Maximum vertical micromotion between bone segments was below 200 μm in all experiments and significantly larger in the implant without a tooth. Differences between plate designs generally became apparent only at 2 BW loading. Results suggest that with compressive loading of 2 BW, long spacer plates experience the lowest implant stresses, and spacer plates (long or short) result in smaller wedge micromotion, potentially beneficial for healing. Values are sensitive to subject bone geometry, highlighting the need for subject-specific modeling. This study demonstrates the benefits of using image-based FE modeling and bone theory to fine-tune HTO implant design.

Biomechanical effect of a lateral hinge fracture for a medial opening wedge high tibial osteotomy: finite element study

“…It is important to highlight the three main advantages of the present study. First, only the tibia was modeled in previous studies that simulated an HTO plate [19][20][21][22]30]. However, a proper knee joint, including soft tissue, was modeled in the present study.…”

“…However, a proper knee joint, including soft tissue, was modeled in the present study. Second, the initial FE model was validated before simulation in this study, whereas the FE model was not validated in previous studies [19][20][21][22]30]. Third, the bonding condition was applied between the bone and screw, and this was assumed to be a bone union, although it does not correspond to a realistic simulation.…”

“…Third, the bonding condition was applied between the bone and screw, and this was assumed to be a bone union, although it does not correspond to a realistic simulation. Therefore, a contact condition between the bone and screw was applied [19][20][21][22]30].…”

“…This is equivalent to the maximal axial force during the gait cycle [22]. In all tests, the tibia was completely constrained to its distal end [20][21][22] (Fig. 3).…”

“…Furthermore, biomechanical, animal, and clinical studies indicated that an LHF after open wedge HTO caused instability that decreased bone healing and led to correction loss and nonunion, especially with unstable plates [9,[16][17][18]. Currently, computational simulation is widely being used to evaluate the stability of plate design in HTO [19][20][21][22]. The advantages of computational simulation for a single subject are that the effects of types of LHF within the same "person" are determined and that the effects of variables such as weight, height, bony geometry, ligament properties, and plate design are excluded [23].…”