In vivo loss of cement-bone interlock reduces fixation strength in total knee arthroplasties.
Prevention of aseptic loosening of total knee arthroplasties (TKAs) remains a clinical challenge. Understanding how changes in morphology at the implant-bone interface with in vivo service affect implant stability and strength could lead to new approaches to mitigate loosening. Enbloc TKA retrievals and freshly-cemented TKA tibial components were used to determine if the mechanical strength of the interface depended on the amount of cement-bone interlock and the morphology of the supporting bone under the cement layer. Implants were sectioned into small specimens of the cement-interface-bone from under the tibial tray. Micro-CT scans were used to document interlock morphology and architecture of the supporting trabecular bone. Axial compression tests were used to assess mechanical behavior. Postmortem retrievals had lower contact fraction (42 ± 55%) compared to freshly-cemented constructs (121 ± 61%) (p = 0.0008). Supporting bone architecture parameters were not different for the two groups. Increased interface contact fraction and supporting bone volume fraction (BV/TV) were positive predictors of interface strength (r(2)  = 0.72, p = 0.0001). For the same supporting bone BV/TV, postmortem specimens had weaker interfaces; they were also more compliant. Cemented TKAs with in vivo service experience a loss of fixation strength and increased micro-motion due to the loss of cement-bone interlock.
Department of Orthopedic Surgery, State University of New York, Upstate Medical University, 3216 IHP, 750 East Adams Street, Syracuse, New York, 13210.
Jacklyn R
JR
Goodheart
Mark A
MA
Miller
Kenneth A
KA
Mann
D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D001843:Bone Cements; D002484:Cementation; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008422:Materials Testing; D008875:Middle Aged
D001843:Bone Cements
PMMA cement; bone resorption; interface mechanics; knee replacement; loosening