Comparison of five patellar height measurement methods in 90A° knee flexion

The aim of this prospective study was to evaluate the patellar height in 90A degrees knee flexion. A total of 85 patients with 95 knee joints were included in the study. Patellar height was measured according to the Blackburne-Peel, Labelle-Laurin, Insall-Salvati, Linclau, and Caton-Deschamps methods in the whole group and in subgroups based on age, gender, and side. The BP-ratio showed a patella norma in 45 cases, and in 25 cases a patella alta and infera, respectively. The Labelle-Laurin method determined a patella norma in eight knees, in 35 a patella alta and in 52 a patella infera. The IS-ratio revealed a patella norma in 52 patients, a patella alta in six and in 37 a patella infera. The Linclau method demonstrated in 52 cases a patella norma, in 17 a patella alta and in 26 a patella infera. The CD-ratio showed the highest values of a patella norma among all tested methods in 67 knees, whereas a patella alta was evident in 13 and a patella infera in 15 cases. In the subgroups, discrepancies depended on the subgroup and method used. Our results demonstrate a method-dependent discrepancy in the measurement of patellar height. A future study should evaluate this effect in a direct comparison between 30A degrees and 90A degrees knee flexion.