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] mu epsilon) to a tensile strain without the wedge (mean [SD] = 12.9 [23] mu epsilon). 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) mu epsilon when the insert was utilised to 23.7 (55.7) mu epsilon 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.