PATELLAR HEIGHT RATIOS - COMPARISON OF 4 MEASUREMENT METHODS

Three blinded observers on three separate occasions calculated four co mmonly employed patellar height ratios on the knees of 15 patients who had three lateral radiographs each. The observers used the same measu rement instrument, a hand-held goniometer ruler, to determine the rela tive reliability of each patellar height ratio, The measurements by th e three observers were examined, and the error and reliability of the four methods of measurement were tested statistically. Among the four methods of measuring patellar height that we studied, the Blackburne-P eel method most consistently reproduced the patellar height index. Int erobserver measurement error averaged 0.06 for all ratios, Values grea ter than 0.06 represented real patellar height changes. The ratios wer e not significantly affected by the change of knee flexion angle from 30 degrees to 50 degrees. Side-to-side patellar height measurement dif ferences averaged 0.16, which suggests that the healthy contralateral limb is not reliable as a control, Mild arthritic changes decreased va riability of measurements by an average of 24% because small osteophyt es better defined the articular margins of the patella.