Comparison of theoretical fixation stability of three devices employed in medial opening wedge high tibial osteotomy: a finite element analysis
1 Department of Orthopaedic Surgery, Zaporozhye State Medical University, Mayakovskyi avenue 26, Zaporozhye, Zaporozhye Oblast 69035, Ukraine
2 Department of Orthopaedic Surgery, Vienna Private Clinic, Pelikangasse 15, Vienna 1090, Austria
3 Department of Traumatology, Landeskrankenhaus Feldkirch, Carinagasse 47, Feldkirch 6807, Austria
4 Institute for Surgical Technology and Biomechanics, University of Bern, Stauffacherstrasse 78, Bern 3014, Switzerland
5 Prydniprovs’ka State Academy of Civil Engineering and Architecture, 1997-2013 24a, Chernyshevs’kogo St, Dnipropetrovs’k 49600, Ukraine
6 Department of Orthopaedic Surgery, Sonnenhof Hospital, Buchserstrasse 30, Bern 3006, Switzerland
7 Institute for Evaluative Research in Medicine, University of Bern, Stauffacherstrasse 78, Bern 3014, Switzerland
BMC Musculoskeletal Disorders 2014, 15:230 doi:10.1186/1471-2474-15-230Published: 10 July 2014
Medial open wedge high tibial osteotomy is a well-established procedure for the treatment of unicompartmental osteoarthritis and symptomatic varus malalignment. We hypothesized that different fixation devices generate different fixation stability profiles for the various wedge sizes in a finite element (FE) analysis.
Four types of fixation were compared: 1) first and 2) second generation Puddu plates, and 3) TomoFix plate with and 4) without bone graft. Cortical and cancellous bone was modelled and five different opening wedge sizes were studied for each model. Outcome measures included: 1) stresses in bone, 2) relative displacement of the proximal and distal tibial fragments, 3) stresses in the plates, 4) stresses on the upper and lower screw surfaces in the screw channels.
The highest load for all fixation types occurred in the plate axis. For the vast majority of the wedge sizes and fixation types the shear stress (von Mises stress) was dominating in the bone independent of fixation type. The relative displacements of the tibial fragments were low (in μm range). With an increasing wedge size this displacement tended to increase for both Puddu plates and the TomoFix plate with bone graft. For the TomoFix plate without bone graft a rather opposite trend was observed.
For all fixation types the occurring stresses at the screw-bone contact areas pulled at the screws and exceeded the allowable threshold of 1.2 MPa for at least one screw surface. Of the six screw surfaces that were studied, the TomoFix plate with bone graft showed a stress excess of one out of twelve and without bone graft, five out of twelve. With the Puddu plates, an excess stress occurred in the majority of screw surfaces.
The different fixation devices generate different fixation stability profiles for different opening wedge sizes. Based on the computational simulations, none of the studied osteosynthesis fixation types warranted an intransigent full weight bearing per se. The highest fixation stability was observed for the TomoFix plates and the lowest for the first generation Puddu plate. These findings were revealed in theoretical models and need to be validated in controlled clinical settings.