Early cement damage around a femoral stem is concentrated at the cement/bone interface.
This study aimed to improve understanding of the mechanical aspects of cemented implant loosening. After aggressive fatigue loading of stem/cement/femur constructs, micro-cracks and stem/bone micro-motions were quantified to answer three research questions: Are cracks preferentially associated with the stem/cement interface, the cement/bone interface or voids? Is cement damage dependent on axial position? Does cement damage correlate with micro-motion between the stem and the bone? Eight Charnley Cobra stems were implanted in cadaveric femora. Six stem/cement/femur constructs were subjected to "stair-climbing" loads for 300 kcycles at 2Hz. Loads were normalized by construct stiffness to avoid fracture. Two additional constructs were not loaded. Transverse sections were cut at 10mm intervals, stained with a fluorescent dye penetrant and examined using epi-fluorescence stereomicroscopy. Crack lengths and cement areas were recorded for 9 sections per specimen. Crack length-density was calculated by dividing summed crack length by cement mantle area. To isolate the effect of loading, length-density data were offset by the baseline length-density measured in the non-loaded specimens. Significantly more cracks were associated with the interdigitated area (35.1%+/-11.6%) and the cement/bone interface (31.0%+/-6.2%) than with the stem/cement interface (11.0%+/-5.2%) or voids (6.1%+/-4.8%) (p<0.05). Load-induced micro-crack length-density was significantly dependent on axial position, increasing proximally (p<0.001). Micro-motions were small, all stems rotated internally. Cement damage did not correlate with micro-motion.
Race
Amos
A
Musculoskeletal Science Research Center, Institute for Human Performance, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA. racea@upstate.edu
Miller
Mark A
MA
Ayers
David C
DC
Mann
Kenneth A
KA
D000368:Aged; D000369:Aged, 80 and over; D001843:Bone Cements / Q000009:adverse effects; D002102:Cadaver; D002484:Cementation / Q000009:adverse effects*; D019544:Equipment Failure Analysis / Q000379:methods; D005264:Femoral Fractures / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology; D015775:Fractures, Stress / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009038:Motion; D011475:Prosthesis Failure; D012016:Reference Values; D012680:Sensitivity and Specificity; D016474:Weight-Bearing
D001843:Bone Cements