Inter-observer variability and its correlation to experience in measurement of lower limb mechanical axis on long leg radiographs

IntroductionRestoration of mechanical axis (MA) is one of the most important aims of treatment of knee arthritis. The measurement of MA is often done on hip knee ankle (HKA) radiographs (LLR), but its measurement is often difficult and variable. We studied to check if inter-observer variability in the measurement of MA is dependent on the experience of the observer.Materials and methods48 patients (70 knees) underwent measurement of MA on HKA radiographs. The measurement was done by five observers of different experience. All the results were tested for inter-observer variability.ResultsThe overall intra-class correlation was 0.70. The two full time consultants had good agreeability among them (p < 0.456). All the surgeons who had less than five years of experience among them also had good agreeability amongst them (all p values >0.005). All the other groups (except senior consultant and senior registrar) had statistically significant difference amongst them (all p values <0.005).ConclusionThere is an inter-observer variability in the measurement of MA on the HKA radiographs. The agreeability between the observers increases as the experience of the personnel increases. Although long leg radiographs can be used for assessment for HKA, this variability should be kept in mind while using this as a tool for planning management of the arthritic knee.