Abstract
Aim: Severity of knee osteoarthritis (OA) can be defined clinically, radiologically, or pathologically. The Système Française D’Arthroscopie (SFA) is a validated method of grading and scoring the severity of changes on the articular surface as observed through the arthroscope. We have validated a modification of the SFA system for use with digital photographs of pathological samples.
Material and Method: After Ethics Committee approval, both tibial plateaux and femoral condyles were collected from 84 patients undergoing total knee replacement or at post mortem. Extent and grading of cartilage changes were documented for the 4 compartments of each sample on a diagram using direct visualisation and probing (Pathological Scores). In addition, each sample was digitally photographed at standard magnification and illumination, archived, graded and scored (Photographic Scores). A second observer (AY) also graded and scored photographic images for 72 compartments of the first 18 cases.
Data analysis: Repeatability was measured as Repeatability Coefficients (Bland and Altman, Lancet1986; 1; 307–10). 95% of the differences between 2 measurements of a case are expected to fall within the Repeatability Coefficient. Associations between compartments are expressed as Pearson correlation coefficients.
Results: For each of the 4 compartments studied, scores ranged from -2.2 to +717.8, representing the full range of possible scores. Allocation of scores to diagrams was highly repeatable (Repeatability Coefficient = 50). There was good agreement between Pathological and Photographic Scores (Repeatability Coefficient = 88). There was moderate agreement between Photographic Scores allocated by the 2 observers, with greatest agreement for low (< 200) and high (> 500) scores. Scores for each compartment correlated with scores for each of the other 3 compartments (R values 0.7 to 0.9, all P < 0.005).
Conclusion: Our modified SFA system permits scoring of OA severity using digital photographs of pathological samples. Our data support the view that OA affects the entire joint, and that a single compartment (e.g. medial tibial plateau) can be taken as broadly representative of the tibiofemoral joint as a whole.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
