Computerised measurement of tibiofemoral alignment

Tibiofemoral alignment has a direct correlation with the survival of total knee arthroplasty. Traditionally, it has been measured using a goniometer o n radiographs. We describe new software which measures this alignment on sc anned radiographs by automatically detecting bones in the image. Two surgeons used conventional methods and two clerical officers used the c omputerised routine to assess 58 radiographs of the knee on two occasions. There were no significant differences between any of the paired comparisons . The largest mean difference detected was 1.19 degrees. Across all compari sons, the mean correlation was 0.755. A standardised routine for measuring tibiofemoral alignment was the greatest factor in reducing error in our stu dy. These results show that non-medical staff can reliably use the software to measure tibiofemoral alignment. It has the potential to measure all the par ameters recommended by the Knee Society.