Clinical value of SPECT/CT in the ‘unhappy’ total knee arthroplasty (TKA)- a prospective study in a consecutive series of 100 painful knees after TKA

AIMS AND OBJECTIVES: Bone SPECT/CT is considered as beneficial hybrid imaging modality in unhappy patients with pain, stiffness or swelling after total knee arthroplasty (TKA). The purpose of this study was to identify typical pattern of tracer uptake distribution and intensity values in these patients after TKA. The above findings were correlated with the type of TKA, the time from primary TKA, fixation of TKA (cemented or non-cemented) and intraoperative findings at revision surgery (loose vs well fixed TKA components). MATERIALS AND METHODS: A total of 100 knees (mean age±standard deviation 70±11 years) of 84 consecutive patients who have previously undergone primary TKA and complained about postoperative knee pain or stiffness after TKA were prospectively included. All patients underwent clinical and radiological examination including standardized radiographs and Tc-99m-HDP-SPECT/CT as part of a routine diagnostic algorithm. The diagnosis before and after SPECT/CT imaging, as well as the final treatment were recorded. Femoral and tibial TKA component position (varus-valgus, flexion-extension, internal rotation-external rotation) was determined on 3D reconstructed images using a customized analysis software. Intensity and anatomical distribution of 99mTc-HDP-SPECT/CT bone tracer uptake was determined using a validated localisation scheme. Maximum intensity values were recorded as well as ratios between the respective value and the background tracer activity (proximal mid-shaft of the femur). Level of significance was p<0.05. Univariate analysis (Chi square test, Pearson correlation, t-test for independent samples) was performed to identify any correlations between component position, tracer uptake and diagnosis. For all analysis, p<0.05 was considered statistically significant. RESULTS: SPECT/CT changed the clinical diagnosis and final treatment in 85/100 (85%) knees. 33 knees (33%) were surgically revised, 58 knees (58%) non-surgically treated and 9 knees (9%) were scheduled for revision surgery. Intraoperative findings confirmed the preoperative SPECT/CT diagnosis in 32/33 knees (97%). Femoral and tibial TKA loosening as well as progression of patellofemoral OA was correctly diagnosed in 100% of knees. Typical patterns of uptake distribution for specific pathologies were identified. Loose femoral TKA components significantly correlated with increased bone tracer uptake only at the lateral femoral regions (p<0.05). Loose tibial TKA components significantly correlated with increased bone tracer uptake at all tibial regions (p< 0.05) and around the tibial peg (p >0.01). CONCLUSION: The diagnostic benefits of SPECT/CT in patients after total knee arthroplasty have been proven. Typical pathology related bone tracer uptake patterns were identified, which will improve reporting quality. Due to the benefits in establishing the correct diagnosis SPECT/CT, when performed and analysed as described here, offers, it is our belief that it should be part of the routine diagnostic algorithm for patients with pain after TKA.