title: Normal range of osteoblastic activity in total hip arthroplasties on single-photon emission computed tomography bone scintigraphy.
abstract: OBJECTIVE
  Knowledge of the normal range of periprosthetic osteoblastic activity around total hip arthroplasties is required for rational diagnosis of complications. The aim of this study was to establish such a normal range for single-photon emission computed tomography (SPECT). Clinical utility of such a range is confident differentiation of normal from abnormal arthroplasties.
  
  
  METHODS
  A total of 122 asymptomatic acetabular cups (age: 0-22 years) and 71 femoral stems (age: 0-20 years) were scanned with SPECT/CT. Two acetabular and three femoral activity ratios to normal reference bone were defined [acetabular axial (AA/RA), acetabular coronal (AC/RA), RA=reference acetabulum; femoral calcar (FC/RF), femoral mid-stem (FM/RF), femoral stem tip (FS/RF), RF=reference femur]. Upper cut-off of normal was defined as mean +3 SD (rounded). Two time breakpoints were analysed (12 and 24 months).
  
  
  RESULTS
  The upper cut-off for the normal range was 1.0 for AA/RA, 1.5 for AC/RA and 2.2 for all thee of FC/RF, FM/RF and FS/RF. AA/RA, FM/RF and FS/RF showed no statistically significant temporal trends. AC/RA showed stabilization of activity after 12 months and FC/RF after 24 months.
  
  
  CONCLUSIONS
  Measured activity ratios that fall within our normal range are likely to represent normal periprosthetic osteoblastic activity. Measured activity ratios that fall above the upper cut-offs of our normal range are likely to be abnormal. The cut-offs are robust in clinical practice and have utility in discriminating normal from abnormal stabilized arthroplasties where visual interpretation is ambiguous. Elevated AC/RA under 12 months and FC/RF under 24 months may represent normal periprosthetic activity and should be interpreted with caution.
authors.affiliation: aDepartment of Diagnostic Imaging, Monash Health, Melbourne bLake Imaging, St. John of God Hospital, Ballarat, Victoria cDepartment of Anatomy and Neuroscience, the University of Melbourne, Parkville, Victoria dUniversity of Notre Dame, Sydney, New South Wales, Australia eDepartment of Nuclear Medicine, National Cancer Institute, Cairo University, Cairo, Egypt fDepartment of Pharmacology and Pharmacy, Centre for Safe Medication Practice and Research, Li Ka Shing Faculty of Medicine, the University of Hong Kong, Hong Kong.
authors.forename: Senpei
authors.initials: S
authors.lastname: Jin
authors.forename: Raef R
authors.initials: RR
authors.lastname: Boktor
authors.forename: Kenneth
authors.initials: K
authors.lastname: Kc Man
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Pitman
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging; D000368:Aged; D015331:Cohort Studies; D005269:Femur / Q000000981:diagnostic imaging; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D010006:Osteoblasts / Q000166:cytology*; D011475:Prosthesis Failure; D012016:Reference Values; D012189:Retrospective Studies; D000072098:Single Photon Emission Computed Tomography Computed Tomography; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon