Finite element analysis of the effect of tibial prosthesis extension stem length in total knee arthroplasty in the Chinese population

Abstract

BackgroundThis study aimed to determine the longest usable range of tibial prosthesis extension stems in Chinese patients undergoing primary total knee arthroplasty and to analyze the effect of different stem lengths on prosthesis stability within this range.MethodsWe conducted three-dimensional modeling and simulated surgery in patients with genu varum to measure the longest usable range of tibial prothesis stems, identify impinged cortices under tibial posterior slope cut of 0° and 3°, and analyze factors influencing the longest stem length. We built finite element models according to the longest usable range of extension stems to simulate tibial prostheses with different stem lengths, measure the stress distribution of tibias and prostheses and the relative displacement of distal ends of prostheses, and investigate the effect of different stem extension lengths on prosthesis stability.ResultsWe simulated osteotomy with a tibial posterior slope cut of 0° and 3°, under which the maximum tibial prosthesis stem length was 83 mm (79±24 mm). The simulated tibial cut with a tibial posterior slope of 3° indicated the maximum tibial prosthesis stem length to be 83 mm (83±20 mm). According to the longest usable range of extension stems, we defined five groups for finite element analysis with 40-mm, 50-mm, 60-mm, 70-mm, and 80-mm stem lengths and analyzed each group for posterior slopes of 0° and 3°. The 80-mm stem length models showed minimum relative displacement of the distal end of tibial prosthesis (0°: 2.63, 1.61±0.05 µm; 3°: 1.48, 1.44±0.09 µm), whereas the 40-mm stem length models showed maximum relative displacement (0°: 3.16, 3.19±0.12 µm; 3°: 1.84, 1.81±0.07 µm). As the length of tibial prosthesis stems increased from 40 to 70 mm, the relative displacement of the distal end of prosthesis decreased for both posterior slopes but was insignificant when stem lengths increased to 70–80 mm.ConclusionsBased on the results, we suggest that using the longest tibial stem is not always necessarily a better option to increase stability, as the prosthesis shows greater stability in only a specific range of increased length but shows insignificant change when the length is greatly increased.