Cobalt in periprosthetic soft tissue. Observations in 6 revision cases

Cobalt (Co) was analyzed in sera obtained before surgery and in biopsies of periarticular soft tissue from 7 control patients undergoing primary total hip arthroplasty and from 6 Co-exposed patients who developed aseptic loosening of the femoral component after hip arthroplasty (CoCrMo alloy, greater than 59 percent Co, metal-on-plastic type). Serum-Co concentrations were not elevated in the Co-exposed patients compared with control patients or healthy adults. In 5 of the 6 Co-exposed patients, Co concentrations were greatly increased in periprosthetic tissue sections 0-1 mm from the synovial surface (median 2.4 [2.1-27] micrograms Co/g) compared with corresponding sections from the control patients (median 0.4 [0.1-0.6] microgram Co/g). Co concentrations diminished in tissue sections at successive distances of 2-3 and 4-5 mm from the synovial surfaces. In the Co-exposed patients, Co concentrations in sera and periprosthetic soft tissues were not correlated, indicating that serum Co concentration is not a reliable index of the Co burden in periprosthetic soft tissue.