The effect of plate design, bridging span, and fracture healing on the performance of high tibial osteotomy plates

Abstract

ObjectivesOpening wedge high tibial osteotomy (HTO) is an established surgical procedure for the treatment of early-stage knee arthritis. Other than infection, the majority of complications are related to mechanical factors – in particular, stimulation of healing at the osteotomy site. This study used finite element (FE) analysis to investigate the effect of plate design and bridging span on interfragmentary movement (IFM) and the influence of fracture healing on plate stress and potential failure.Materials and MethodsA 10° opening wedge HTO was created in a composite tibia. Imaging and strain gauge data were used to create and validate FE models. Models of an intact tibia and a tibia implanted with a custom HTO plate using two different bridging spans were validated against experimental data. Physiological muscle forces and different stages of osteotomy gap healing simulating up to six weeks postoperatively were then incorporated. Predictions of plate stress and IFM for the custom plate were compared against predictions for an industry standard plate (TomoFix).ResultsFor both plate types, long spans increased IFM but did not substantially alter peak plate stress. The custom plate increased axial and shear IFM values by up to 24% and 47%, respectively, compared with the TomoFix. In all cases, a callus stiffness of 528 MPa was required to reduce plate stress below the fatigue strength of titanium alloy.ConclusionWe demonstrate that larger bridging spans in opening wedge HTO increase IFM without substantially increasing plate stress. The results indicate, however, that callus healing is required to prevent fatigue failure.Cite this article: A. R. MacLeod, G. Serrancoli, B. J. Fregly, A. D. Toms, H. S. Gill. The effect of plate design, bridging span, and fracture healing on the performance of high tibial osteotomy plates: An experimental and finite element study. Bone Joint Res 2018;7:639–649. DOI: 10.1302/2046-3758.712.BJR-2018-0035.R1.

Effect of Plate Type and Working Length on a Synthetic Compressed Juxta-Articular Fracture Model

“…While the authors acknowledged this confounding factor, we believe that these results have been misinterpreted in the literature. 11,13 We believe the fracture conditions modelled by Stoffel and colleagues 6 are unlikely to be realistic for a clinical situation. Eccentric axial loading producing only tension bending in a small gap, transverse fracture without concurrent torsional and compressive loads would be an unlikely clinical scenario.…”

“…These findings are consistent with other studies that demonstrated greater construct stiffness with shorter working lengths. [6][7][8][9][10][11]31 Plate strain was determined at twelve ROI using digital image correlation for both plate types under compression bending and torsion. At no ROI, mean plate strain was reduced by increasing working length under either load direction.…”

“…15,20,28,29,32,33 Despite these previous biomechanical studies, the relationship between plate strain and working length remains controversial in the literature. 11,12,14,34 This controversy is generated from work using a non-compressed 1 mm fracture gap model where plate stress was calculated in an analytical fine element analysis model loaded under axial compression producing tension bending. 6 In that modelling, increasing the working length paradoxically reduced plate strain that was explained by early interfragmentary contact across the transcortical gap creating load-sharing and thereby increased construct stiffness and decreased plate strain.…”

“…4,5 Plate working length is one of the factors that affects construct stability. [6][7][8][9][10][11] Working length is affected by size of the fracture gap, plate stand-off distance, distance between the innermost screws and load direction. The effect of working length on construct stability and plate strain/stress is still the subject of some controversy.…”

“…The effect of working length on construct stability and plate strain/stress is still the subject of some controversy. [11][12][13][14] A finite element analysis study demonstrated that a longer working length increased plate stress in a 6 mm fracture gap model, though paradoxically reduced plate stress in a 1 mm fracture gap model, during axial compression producing tension bending. 6 Much of the information on the effect of working length on plate strain/stress is based on fracture gap models, [6][7][8]15,16 with no information from compressed fracture models.…”