99mTc-diphosphonate scintigraphy in successful knee arthroplasty and its relation to micromotion.

Nineteen tibial components after successful knee arthroplasty were studied with technetium 99m scintigraphy. All cases were also followed from the operation with roentgen stereophotogrammetric analysis (RSA). All but three cases became stable after an initial period of migration. Scintigraphic uptake was found in all cases, with a ratio as high as seven in the medial compartment and three in the lateral compartment. A group of cases with proven mechanical loosening showed an uptake ratio as high as 6.9 in the medial compartment and 5.5 in the lateral compartment. No correlation was found between scintigraphic uptake and alignment, whether cement was used, or the presence/absence of migration. Technetium 99m scintigraphy is not a useful method for assessing loosening in individual symptomatic cases of knee arthroplasty.