Assessing the validity of the modified Blumensaat method for radiographic evaluation of patellar height.

Abstract

Although several indexes have been used for patellar height evaluation, the literature on patellar height evaluation using a femoral reference point is scant. We have previously reported on a new index, the modified Blumensaat (MB) method, which evaluates the patellar height using a femoral reference point. The purpose of this study was to evaluate the validity of the MB method. In addition to 10 volunteers (group C), 10 men (group M) and 10 women (group F) who underwent knee surgery were selected for the study. The Insall-Salvati (IS), modified IS (MIS), Blackburne-Peel (BP), MB, and modified intercondylar-shelf-angle-corrected Blumensaat (MIB) ratios were measured on lateral knee radiographs with the knee in 30°, 40°, and 50° flexion. In group C, the MB and MIB ratios were similar; the IS ratio was not dependent on the knee flexion angle, and there was no significant difference in the MIS and BP ratios between 40° and 50° of knee flexion and in the MB and the MIB ratios between 30° and 40° of knee flexion. There were no differences between group M and group F with respect to any of the indexes. Furthermore, the differences in all indexes among the different knee flexion angles, in groups M and F, were similar to those in group C. The MB method is applicable for patellar height evaluation and is recommended with a knee flexion angle of 30°-40°.