title: A novel standardized algorithm using SPECT/CT evaluating unhappy patients after unicondylar knee arthroplasty--a combined analysis of tracer uptake distribution and component position.
abstract: BACKGROUND
  The introduction of a standardized SPECT/CT algorithm including a localization scheme, which allows accurate identification of specific patterns and thresholds of SPECT/CT tracer uptake, could lead to a better understanding of the bone remodeling and specific failure modes of unicondylar knee arthroplasty (UKA). The purpose of the present study was to introduce a novel standardized SPECT/CT algorithm for patients after UKA and evaluate its clinical applicability, usefulness and inter- and intra-observer reliability.
  
  
  METHODS
  Tc-HDP-SPECT/CT images of consecutive patients (median age 65, range 48-84 years) with 21 knees after UKA were prospectively evaluated. The tracer activity on SPECT/CT was localized using a specific standardized UKA localization scheme. For tracer uptake analysis (intensity and anatomical distribution pattern) a 3D volumetric quantification method was used. The maximum intensity values were recorded for each anatomical area. In addition, ratios between the respective value in the measured area and the background tracer activity were calculated. The femoral and tibial component position (varus-valgus, flexion-extension, internal and external rotation) was determined in 3D-CT. The inter- and intraobserver reliability of the localization scheme, grading of the tracer activity and component measurements were determined by calculating the intraclass correlation coefficients (ICC).
  
  
  RESULTS
  The localization scheme, grading of the tracer activity and component measurements showed high inter- and intra-observer reliabilities for all regions (tibia, femur and patella). For measurement of component position there was strong agreement between the readings of the two observers; the ICC for the orientation of the femoral component was 0.73-1.00 (intra-observer reliability) and 0.91-1.00 (inter-observer reliability). The ICC for the orientation of the tibial component was 0.75-1.00 (intra-observer reliability) and 0.77-1.00 (inter-observer reliability).
  
  
  CONCLUSIONS
  The SPECT/CT algorithm presented combining the mechanical information on UKA component position, alignment and metabolic data is highly reliable and proved to be a valuable, consistent and useful tool for analysing postoperative knees after UKA. Using this standardized approach in clinical studies might be helpful in establishing the diagnosis in patients with pain after UKA.
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laifen), CH-4101, Bruderholz, Switzerland. basil.suter@unibas.ch.
authors.forename: Basil
authors.initials: B
authors.lastname: Suter
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laifen), CH-4101, Bruderholz, Switzerland. Enrique.Testa@unibas.ch.
authors.forename: Enrique
authors.initials: E
authors.lastname: Testa
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laifen), CH-4101, Bruderholz, Switzerland. Patrick.staempfli@ksbl.ch.
authors.forename: Patrick
authors.initials: P
authors.lastname: Stämpfli
authors.affiliation: Department of Radiology, Plymouth, UK. pkonala@nhs.net.
authors.forename: Praveen
authors.initials: P
authors.lastname: Konala
authors.affiliation: Institute for Radiology and Nuclear Medicine, Kantonsspital Baselland, Bruderholz, CH-4101, Switzerland. helmut.rasch@unibas.ch.
authors.forename: Helmut
authors.initials: H
authors.lastname: Rasch
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laifen), CH-4101, Bruderholz, Switzerland. niklaus-f.friederich@unibas.ch.
authors.forename: Niklaus F
authors.initials: NF
authors.lastname: Friederich
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Kantonsspital Baselland (Bruderholz, Liestal, Laifen), CH-4101, Bruderholz, Switzerland. michael.hirschmann@unibas.ch.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Hirschmann
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D018771:Arthralgia / Q000175:diagnosis* / Q000209:etiology; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D019544:Equipment Failure Analysis / Q000379:methods; D005260:Female; D006240:Happiness; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000592:standards; D020370:Osteoarthritis, Knee / Q000150:complications / Q000175:diagnosis* / Q000601:surgery*; D010147:Pain Measurement / Q000379:methods; D017060:Patient Satisfaction; D011475:Prosthesis Failure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D015899:Tomography, Emission-Computed, Single-Photon / Q000592:standards*; D014057:Tomography, X-Ray Computed / Q000592:standards*; D016896:Treatment Outcome