Metal levels in cemented total hip arthroplasty. A comparison of well-fixed and loose implants.
In a prospective study, synovial fluid metal levels from stainless steel, cobalt-chromium, and titanium-alloy cemented total hip implants were measured. There were 37 well-fixed and 44 loose hip arthroplasties. Tissue-metal levels were quantitated in the cases revised for loosening. Retrieval analysis for implant wear was performed. Synovial fluid analysis showed a fivefold increase in metal levels of loose compared with well-fixed stainless steel implants. There was a sevenfold increase in metal levels of loose compared with well-fixed cobalt-chromium implants. There was a 21-fold increase in metal levels of loose compared with well-fixed titanium-alloy (Ti-6Al-4V) implants. Tissue-metal levels from revised cobalt-chromium implants averaged 45 micrograms/g dry tissue weight compared to 4,470 micrograms/g dry tissue weight from revised titanium-alloy implants, a 100-fold increase. Implant retrieval analysis showed severe burnishing and scratching in all titanium-alloy femoral heads and extensive burnishing and scratching in the majority of the femoral stems. Well-fixed cemented implants have similar low synovial fluid metal levels. However, when loosening of implants occurs, titanium-alloy implants release disproportionate levels of metal into synovial fluid and local tissues compared to stainless steel or cobalt-chromium.