Retrieval analysis of modular total knee replacements: factors influencing backside surface damage

Retrieved knee implants were examined to investigate the influence of patient and implant related factors on backside damage. Fifty-two implants of three different models were examined that all had cemented tibial trays without screw holes. A semi-quantitative grading system supplied backside damage scores (BDS) for each polyethylene (PE) tibial insert. Evidence was obtained to support the use of a constraining partial-peripheral locking mechanism and polished tibial tray surface (particularly for male patients) to reduce backside damage. Overall, male patients in the present study were associated with higher body mass and higher BDS compared with female patients. Furthermore, PE inserts sterilized by gamma-in-air had higher BDS than PE inserts sterilized in inert environments (gas-plasma or ethylene-oxide). Also, the proximal surfaces of tibial trays that had been grit-blasted showed embedded particles that may have increased backside damage. While none of these overall findings was unexpected, the present study provided detailed supporting analysis based on data from clinical retrievals, which may further support the use of a polished tibial tray combined with partial-peripheral locking mechanism to reduce BDS.