Blumensaat line and patellar height

Obj ectiv e s: We investigated the agreement between the Blumensaat method and patellar height ratios and evaluated the reliability of the method in patellar height measurements. Methods: We retrospectively evaluated 105 digital knee x-rays of 77 patients (23 males, 54 females; mean age 32 years; range 21 to 62 years), whose radiographs were obtained at 30° of knee flexion. Patellar heights were measured with the use of the Blumensaat, Insall-Salvati, modified Insall-Salvati, and Blackburne-Peel methods. Patellar height was also evaluated after standardization of the angle between the femoral shaft and the Blumensaatʹs line (corrected Blumensaat method). Agreement and cor¬relations were sought between the qualitative and quanti¬tative results of the methods, respectively. Resul t s: When the qualitative results were considered, agree¬ment of the Blumensaat method was very weak with the Insall-Salvati, modified Insall-Salvati, and Blackburne-Peel methods (kappa coefficients: 0.21, -0.14, and 0.12, respec¬tively). The corrected Blumensaat method also had a very weak agreement with the other indices (kappa coefficients: 0.27, -0.11, and 0.13, respectively). Correlation analyses of the quantitative results showed very weak to moderate corre¬lations between the methods used. The Blumensaat method was relatively well correlated with the modified Insall-Salvati method (r=0.514, p<0.05). Correlations were weak to moder¬ate between the patellar height indices, the highest correlation being between the modified Insall-Salvati and Blackburne- Peel methods (r=0.557, p<0.05). Conclusion: The results of the patellar height measure¬ments obtained by the Blumensaat method do not agree with widely used patellar height indices.