Bone loss associated with the use of spacer blocks in infected total knee arthroplasty

Twenty-five knees in 24 patients with infected total knee replacements were treated with debridement, component removal, and insertion of an antibiotic impregnated cement spacer block. Intravenous antibiotics were administered for 6 weeks during which time the patients' knees were kept in a knee immobilizer nonweightbearing. These cases were reviewed retrospectively to determine radiographically the amount of bone loss that occurred during the period before reimplantation. Tibial and femoral bone loss occurred frequently from invagination of the cement spacer block into the femoral and tibial cancellous bone. Tibial bone loss was present in 10 (40%) cases and averaged 6.2 mm. Femoral bone loss was present in 11 (44%) cases and averaged 12.8 mm. Bone loss was more common when spacer blocks were undersized. None of the 15 spacer blocks that were made with a small intramedullary stem displaced. Three of the remaining 10 spacer blocks made without an intramedullary stem did displace with associated bone loss. Antibiotic spacer blocks used in the two-stage treatment of infected total knee replacements can be associated with subsequent tibial and femoral bone loss.