3-PHASE BONE-SCAN PATTERN IN ASYMPTOMATIC UNCEMENTED TOTAL KNEE ARTHROPLASTY

In this study we investigated the bone scan pattern in a homogeneous g roup of asymptomatic patients implanted with the same type of total kn ee arthroplasty (TKA) and with a minimum follow-up of 2 years. Twenty- nine patients (21 females, 8 males, mean age 62 years), with a total o f 30 uncemented Hofmann TKAs, were entered in the study. The rime inte rval from surgery to scintigraphic evaluation ranged from 2 to 4 years . Bone scan was performed using the three-phase technique and images w ere interpreted by visual analysis using a three-point scale for the d ynamic and blood pool phases and a five-point scale for the bone phase . Areas of increased periprosthetic technetium-99m methylene diphospho nate (MDP) uptake were observed until 4 years after surgery. However, comparing the TKAs implanted 2, 3 and 4 years previously, a decreasing pattern in tracer uptake intensity was noted this being more evident in the femoral and lateral tibial components. In some cases, a persist ently elevated tracer uptake, not exceeding a moderate grade, was foun d in the medial tibial component. In conclusion, increased periprosthe tic Tc-99m-MDP uptake is a common finding in asymptomatic uncemented H ofmann TKAs for a prolonged period after surgery, but the uptake inten sity is generally mild or moderate and shows a characteristic decreasi ng pattern over time. Furthermore, in contrast with other types of asy mptomatic knee implants previously investigated, no case of high or ve ry high bone uptake was recorded with this type of implant. We may spe culate that scintigraphic parameters of normality, and pathology, shou ld be determined for each type of TKA, It is likely that, with the unc emented Hofmann TKA, a high or very high tracer uptake or a progressiv e increase in the uptake intensity is suggestive of the presence of co mplications.