title: Tibiofemoral subchondral surface ratio (SSR) is a predictor of osteoarthritis symptoms and radiographic progression: data from the Osteoarthritis Initiative (OAI).
abstract: OBJECTIVE
  Symptomatic knee osteoarthritis (OA) is poorly correlated with radiographic severity, but subchondral bone measures may be useful for risk assessment as bone shape is grossly unaffected at early radiographic stages. We sought to determine whether compartment-specific size mismatch in the naturally asymmetric tibiofemoral joint, measured as tibiofemoral subchondral surface ratio (SSR): (1) predicts incident symptoms, (2) predicts incident or progressive OA, (3) is reproducible and time invariant.
  
  
  METHODS
  OA Initiative participants with baseline MRIs and up to 48-month follow-up (n = 1,338) were analyzed. Logistic regression was used to determine the association between SSR and incident symptoms, incident OA, and progression of OA after adjusting for demographic, radiologic, injury-related, and lifestyle-related factors. Reproducibility was assessed as % coefficient of variation (CV) on repeat MRI studies at baseline and 24 months.
  
  
  RESULTS
  Increased medial SSR is protective against incident symptoms at 48 months (per 0.1 increase: OR 0.48 CI 0.30, 0.75; P = 0.001). Increased lateral SSR values are protective against lateral OA incidence (OR 0.23 CI 0.06, 0.77; P = 0.016) or progression (OR 0.66 CI 0.43, 0.99; P = 0.049) at 24 months. Both medial and lateral SSR are stable over time (medial: mean change 0.001 SD 0.016; lateral: mean change 0.000 SD 0.017) and are highly reproducible (3.0% CV medial SSR; 2.7% CV lateral SSR).
  
  
  CONCLUSIONS
  A larger medial SSR is protective against developing OA-related symptoms. A larger lateral SSR is protective against lateral OA incidence or progression. Finally, lateral and medial SSR are stable over time and are highly reproducible across MRI studies.
authors.affiliation: Department of Orthopaedics, The Ohio State University, USA. Electronic address: Joshua.Everhart@osumc.edu.
authors.forename: J S
authors.initials: JS
authors.lastname: Everhart
authors.affiliation: Department of Orthopaedics, The Ohio State University, USA; Department of Mechanical and Aerospace Engineering, USA. Electronic address: Siston.1@osu.edu.
authors.forename: R A
authors.initials: RA
authors.lastname: Siston
authors.affiliation: Department of Orthopaedics, Cartilage Restoration Program, Sports Health and Performance Institute, The Ohio State University, USA. Electronic address: david.flanigan@osumc.edu.
authors.forename: D C
authors.initials: DC
authors.lastname: Flanigan
mesh_terms: D000368:Aged; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000473:pathology*; D015331:Cohort Studies; D016001:Confidence Intervals; D018450:Disease Progression; D042241:Early Diagnosis; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology; D005500:Follow-Up Studies; D006801:Humans; D016015:Logistic Models; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging* / Q000473:pathology*; D010147:Pain Measurement; D011237:Predictive Value of Tests; D011859:Radiography; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology; D013997:Time Factors; D016474:Weight-Bearing
keywords: Femoral weight-bearing subchondral surface area: subchondral surface ratio (SSR); Knee osteoarthritis; Osteoarthritis risk factor; Symptomatic osteoarthritis