Symptomatic versus asymptomatic knees after bilateral total knee arthroplasty: what is the difference in SPECT/CT?

PURPOSE: The primary purpose of this retrospective study was to evaluate the differences of bone tracer uptake (BTU) in symptomatic and asymptomatic knees after bilateral total knee arthroplasty (TKA) and identify typical BTU patterns with regards to TKA component position and alignment.

METHODS: A consecutive number of 37 patients after bilateral TKA were retrospectively included. The knees were grouped into symptomatic (group A) and asymptomatic (group B) knees. All patients underwent 99m-Tc-HDP-SPECT/CT. Coronal, rotational, and sagittal TKA component position was analysed in 3D reconstructed CT. BTU was anatomically localised and quantified using a validated standardized localization scheme. Maximum BTU values for each area were recorded and normalized values calculated. Signed log-rank test, chi-square test, paired t-tests, and Pearson correlations were used (p <0.05).

RESULTS: Symptomatic TKAs were significantly more flexed and had a tendency to be more internally rotated when compared to asymptomatic ones (p < 0.05). In all regions, the mean BTU in asymptomatic knees was lower than in symptomatic knees. In both groups the highest mean BTU was found around the tibial stem (symptomatic 7.30; asymptomatic 6.30, p = 0.061) and at the tip of the tibial stem (symptomatic 5.49; asymptomatic 4.74, p = 0.062). Superior patellar regions showed higher BTU than inferior regions. The highest patellar BTU was found in the superior medial patella (symptomatic 4.99; asymptomatic 3.98, p = 0.048). The lowest BTU was found in the posterior femoral regions (flatsp, flatip, fmedsp, fmedip) (Table 3). Tibial and patellar areas showed twice as high mean BTUs than femoral areas (Fig. 3). A significant correlation of TKA component position and BTU was demonstrated.

CONCLUSIONS: Distribution and intensity of BTU in SPECT/CT depends on TKA component position and alignment. In addition, typical BTU patterns in symptomatic and asymptomatic knees were identified. A profound knowledge of BTU pattern, TKA component position, and alignment helps to identify pathologies in patients after TKA.

CLINICAL EVIDENCE: Diagnostic study, level II.