title: The sand rat model for disc degeneration: radiologic characterization of age-related changes: cross-sectional and prospective analyses.
abstract: METHODS
  This report is composed of two studies, one cross-sectional and one prospective cohort study, that analyze the radiologic features of disc degeneration in the sand rat (Psammomys obesus).
  
  
  OBJECTIVE
  To statistically assess progressive disc degeneration in this useful animal model in terms of a cross-sectional study and a prospective monthly evaluation of individual animals.
  
  
  BACKGROUND
  P. obesus is an attractive small rodent model for spontaneous age-related disc degeneration. Because disc degeneration is spontaneous, the model avoids use of chemonucleolysis or surgical injury to cause disc degeneration. Little is understood, however, about specific details of the progressive disc deterioration.
  
  
  METHODS
  This study statistically assessed 158 animals in a cross-sectional study and 22 animals in a longitudinal study, which followed individual animals to 12 months of age. Radiologic features involving irregular disc margins, disc wedging, disc narrowing, endplate calcification, subchondral sclerosis, ligament calcification, and osteophyte formation were studied.
  
  
  RESULTS
  Significant age-related cross-sectional changes were present for all features (P < or = 0.005). Males showed a statistically greater incidence of wedging at 6 and 12 months, wedging at 2 and 6 months, and endplate calcification at 2 months than did females. By 6 months of age, however, endplate calcification had a higher incidence in females than in males. Prospective analysis showed that wedging, narrowing, endplate calcification, and irregular disc margins were more common at 12 months of age than at 2 months (P = 0.0001). By the age of 12 months, all lumbar sites of both males and females showed endplate calcification and the majority of animals showed narrowing and wedging.
  
  
  CONCLUSIONS
  Radiographic signs of degeneration were evident by age 2 months; wedging, narrowing, irregular disc margins, and endplate calcification were the most common degenerative changes in older animals. These data show that the sand rat provides a reliable, useful model of spontaneous disc degeneration.
authors.affiliation: Department of Orthopaedic Surgery , Carolinas Medical Center, Charlotte, North Carolina 28232, USA. hgruber@carolinas.org
authors.forename: Helen E
authors.initials: HE
authors.lastname: Gruber
authors.forename: Tracy
authors.initials: T
authors.lastname: Johnson
authors.forename: H James
authors.initials: HJ
authors.lastname: Norton
authors.forename: Edward N
authors.initials: EN
authors.lastname: Hanley
mesh_terms: D000375:Aging / Q000473:pathology; D000818:Animals; D001835:Body Weight; D002114:Calcinosis / Q000000981:diagnostic imaging; D003430:Cross-Sectional Studies; D004195:Disease Models, Animal; D018450:Disease Progression; D005260:Female; D005849:Gerbillinae; D007403:Intervertebral Disc / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology*; D008137:Longitudinal Studies; D008161:Lumbosacral Region / Q000473:pathology / Q000503:physiopathology; D008297:Male; D011446:Prospective Studies; D011859:Radiography; D012737:Sex Factors; D013122:Spinal Diseases / Q000000981:diagnostic imaging* / Q000473:pathology / Q000503:physiopathology*; D013131:Spine / Q000000981:diagnostic imaging / Q000473:pathology