Alternative method for measuring the mechanical axis of the knee

Objective. To identify the existence of significant differences in the degrees of mal-alignment of the mechanical axis of the knee between a traditional measuring method and an alternative method. Materials and methods. One hundred mechanical axes of the knee were determined in patients of both sexes. The degree of axis mal-alignment was obtained first using the traditional measuring method and subsequently using the alternative method. The results obtained from the two methods were then compared. The measurement variable control was standardised by positioning the patients in the same place during radiography when beginning mechanical axis determination. A wooden ruler on which each centimetre was indicated by a metal strip and numbered at every 10-centimeter interval was used to evaluate the degree of pelvic mal-alignment. The ruler was then used as a mechanical axis correction reference in accordance with the characteristics of each patient. Results. The following results were obtained from 100 mechanical axes evaluated by the traditional method and by the alternative method, respectively: varus deformity of the right pelvic segment was 21 degrees +/- 16 degrees vs. 7 +/- 6 degrees; varus deformity of the left pelvic segment was 22 +/- 17 degrees us. 8 +/- 5; valgus deformity of the right pelvic segment was 21 +/- 15 degrees vs. 8 +/- 6; and valgus deformity of the left pelvic segment was 16 +/- 11 us. 6 +/- 5 degrees. Conclusions. Our results suggest that the proposed method provides more accurate mechanical axis measurement and that the correction is exponential: the greater the angle measured traditionally, the greater the correction with our proposed method.