Background: The introduction of a standardized SPECT/CT algorithm including a localization scheme, which allows\naccurate identification of specific patterns and thresholds of SPECT/CT tracer uptake, could lead to a better\nunderstanding of the bone remodeling and specific failure modes of unicondylar knee arthroplasty (UKA). The\npurpose of the present study was to introduce a novel standardized SPECT/CT algorithm for patients after UKA and\nevaluate its clinical applicability, usefulness and inter- and intra-observer reliability.\nMethods: Tc-HDP-SPECT/CT images of consecutive patients (median age 65, range 48ââ?¬â??84 years) with 21 knees after\nUKA were prospectively evaluated. The tracer activity on SPECT/CT was localized using a specific standardized UKA\nlocalization scheme. For tracer uptake analysis (intensity and anatomical distribution pattern) a 3D volumetric quantification\nmethod was used. The maximum intensity values were recorded for each anatomical area. In addition, ratios between\nthe respective value in the measured area and the background tracer activity were calculated. The femoral and tibial\ncomponent position (varus-valgus, flexion-extension, internal and external rotation) was determined in 3D-CT. The\ninter- and intraobserver reliability of the localization scheme, grading of the tracer activity and component measurements\nwere determined by calculating the intraclass correlation coefficients (ICC).\nResults: The localization scheme, grading of the tracer activity and component measurements showed high inter- and\nintra-observer reliabilities for all regions (tibia, femur and patella). For measurement of component position there was\nstrong agreement between the readings of the two observers; the ICC for the orientation of the femoral component\nwas 0.73-1.00 (intra-observer reliability) and 0.91-1.00 (inter-observer reliability). The ICC for the orientation of the tibial\ncomponent was 0.75-1.00 (intra-observer reliability) and 0.77-1.00 (inter-observer reliability).\nConclusions: The SPECT/CT algorithm presented combining the mechanical information on UKA component position,\nalignment and metabolic data is highly reliable and proved to be a valuable, consistent and useful tool for analysing\npostoperative knees after UKA. Using this standardized approach in clinical studies might be helpful in establishing the\ndiagnosis in patients with pain after UKA.
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