77 SPECT/CT in the post-operative painful knee SPECT/CT after unicondylar knee arthroplasty (UKA) There is only very limited evidence for normal patterns versus patterns on boneSPECT/CT indicating a complication as loosening or infection regarding UKA. A recent prospective study by Suter, et al. including 21 patients specifically investigated SPECT/CT performance in UKA [56]. This study examined uptake patterns after UKA, using a self-designed localization scheme and 3D volumetric quantification of the SPECT/CT images on which, next to BTO, femoral and tibial component position (varus-valgus, flexion-extension, internal and external rotation) were determined on the CT part. The inter- and intraobserver coefficients of agreement using this method were high (all scores 0.73 and higher). Their SPECT/CT algorithm proved reliable and valuable for analyzing postoperative knees after UKA in their patients. Confirmation of this approach in clinical studies is needed to investigate whether establishing the diagnosis in patients with a painful UKA is accurate when using this strategy [56]. SPECT/CT may diagnose both loosening of a part of the UKA, as well as (secondary) OA in other knee compartments (Figure 4). SPECT/CT after total knee arthroplasty Aseptic loosening and other aseptic complications A landmark article on the role of SPECT/CT in the painful knee andmainly focusing on aseptic loosening was published in 2015 by Hirschmann, et al. [34]. This prospective study in 100 patients after TKA clearly described the diagnostic accuracy of SPECT/ CT using novel structured pathology-related 3D-patterns of bone turnover. SPECT/CT was shown to improve diagnosis and treatment in 85% of patients and SPECT/CT diagnosis was confirmed intra-operatively in 97%. Loosening of tibial or femoral components and patello-femoral OA were diagnosed correctly in 100% of the patients. The publication provided a detailed description on the clinical relevance of increased BTO at specific sites [34]. A standardized localization scheme for interpreting BTO on SPECT/CT after TKA has been proposed by Hirschmann, et al., which could be able to relate biomechanical loading to SPECT/CT uptake patterns (Figure 5) [44]. A selection of pivotal structured SPECT/CT findings with direct correlation to clinical relevance is shown in Table 3. As previously reported by the same group, it was concluded that SPECT/CT should be part of the routine diagnostic algorithm for patients with pain after TKA [34]. This will need further confirmation in clinical practice by other groups. 3