Validation And Repeatability Of Computer-assisted Limb X Film Measuring Plate

Objective To introduce the making of the Limb X Film Measuring Plate(LXMP)and its softwares,and to study its validity and repeatability in order to produce a accurate and practical tool and method for clinical X film measurement of limb length and angle.Methods The LXMP was designed.Three known points in nine templates were taken as gold standard, which was compared with measuring results of those projected points on the X film for testing validation of the LXMP.21 knees with osteoarthritis were selected.The length and angle of the lower limbs were measured twice with help of the LXMP by an observer in different time interval for testing intra-observer repeatability.Two observer measured once above films at same time for testing inter-observer repeatability. The correlation coefficients,mean absolute differences between the repeated measurements,and error rate were calculated.Results The points on the LXMP can be seen clearly on X film.Validation tests showed the difference of angle measurement between gold standard and measuring results of those projected points on the X film is very small,with mean absolute differences 0.1°-0.21°,error rate 0.12%-3.15%and r close to 1,and difference of length measurement is also small,with mean absolute differences 0.05cm-0.16cm,error rate 0.12%-0.28%and r close to 1.Intra-observer repeatability test for both angle and length showed r close to 1,mean absolute differences 0.55°and 0.1-0.37cm and error rate 0.31%-0.97%,while inter-observer repeatability test,r close to 1,mean absolute differences 0.39°and 0.05-0.13cm and error rate 0.16%-0.35%.Conclusion The Limb X Film Measuring Plate can be used for accurate measuring of limb length and angle with good validity and repeatability.