Peri‐implant bone strains and micro‐motion following in vivo service: A postmortem retrieval study of 22 tibial components from total knee replacements

Biological adaptation following placement of a total knee replacements (TKRs) affects peri‐implant bone mineral density (BMD) and implant fixation. We quantified the proximal tibial bone strain and implant‐bone micro‐motion for functioning postmortem retrieved TKRs and assessed the strain/micro‐motion relationships with chronological (donor age and time in service) and patient (body weight and BMD) factors. Twenty‐two tibial constructs were functionally loaded to one body weight (60% medial/40% lateral), and the bone strains and tray/bone micro‐motions were measured using a digital image correlation system. Donors with more time in service had higher bone strains (p = 0.044), but there was not a significant (p = 0.333) contribution from donor age. Donors with lower peri‐implant BMD (p = 0.0039) and higher body weight (p = 0.0286) had higher bone strains. Long term implants (>11 years) had proximal bone strains 900 µϵ that were almost twice as high as short term (<5 years) implants 570 µϵ. Micro‐motion was greater for younger donors (p = 0.0161) and longer time in service (p = 0.0008). Increased bone strain with long term in vivo service could contribute to loosening of TKRs by failure of the tibial peri‐implant bone.