P Hernigou , P Filippini ,A Poignard, G Mathieu (Créteil)
Metallic debris from metallosis can compensate for the radiolucency resulting from bony destruction and compromise preoperative diagnosis of osteolysis. We compared the radiological findings in two groups of patients: those with pure osteolysis resulting from polyethylene debris and those with osteolysis associated with metallosis.
MATERIAL AND METHODS
This study compared ten total knee arthroplasties free of metallosis at revision (pathology examination revealed only polyethylene debris) with ten total knee arthroplasties with pathologically confirmed metallosis of the synovium and periprosthetic bony tissue. Revisions were performed for loosening or a femoropatellar problem. At revision, the localization and the degree of tibial and/or femoral osteolysis were noted. Preoperative x-rays were analyzed to search for femoral, tibial or patellar osteolysis and were compared with operative findings. On the AP and lateral views, ten osteolysis zones were defined for each knee (four tibia, five femur, and one patella).
RESULTS
Ten knees had osteolysis associated with polyethylene debris alone. Tibial osteolysis was found intraoperatively in 16 of the 40 theoretically possible localizations and was recognized on the preoperative x-rays in all 16. Femoral osteolysis was found intraoperatively in 18 of the 50 theoretically possible localizations was only recognized in 6 of the 18. For the ten knees with metallosis, tibial osteolysis was found intraoperatively in 22 of the theoretically possible localizations and was recognized on preoperative x-rays in 10 of the 22. Femoral osteolysis was found intraoperatively in 32 of the 50 theoretically possible localizations but was only recognized preoperatively in 5 of the 32. Comparisons between the two groups showed that femoral osteolysis was significantly more difficult to identify preoperatively than tibial osteolysis irrespective of the type of osteolysis (with or without metallosis). Furthermore, in patients with metallosis, it was significantly more difficult to recognize osteolysis preoperatively in both the tibial and femoral localizations.
DISCUSSION
Metallosis can mask the diagnosis of femoral osteolysis and makes it very difficult to recognize tibial osteolysis. Arguments in favor of osteolysis (abnormal skin pigmentation, radio-opaque effusion, abnormal color and density of the joint fluid) are discussed. When the diagnosis of metallosis is established preoperatively, the chances of finding osteolysis intraoperatively are much higher than suggested by the preoperative x-rays.