Intra-observer and inter-observer errors in CT measurement of torsional profiles of lower limbs: a retrospective comparative study

BACKGROUND The purpose of this study was to determine errors in measurement of torsional profiles (TP) (torsional femoral angle, torsional tibial angle, and femoral ankle angle) among four orthopedic surgeons, experts, and non-experts in measurement, and the learning curve. METHODS Twenty-six lower extremities of 13 patients with spastic diplegia candidates for femoral/tibial derotational osteotomy had preoperative bilateral computer tomography (CT) scan grams to establish the TP. Each measurement was done by four orthopedic surgeons, two experienced clinicians and interpreters of CT imaging and two with limited clinical and imaging assessment experiences. Images were blinded and the surgeons made three determinations at least 5 days apart; the three angles were measured each time for each limb. Intra-observer and inter-observer variability were determined using bias, standard deviation, and interclass correlation coefficient. RESULTS Significant inter-observer variability and bias were noted between experts and non-experts (average variability: ICC experts: 0.88 ± 0.15; ICC non-experts: 0.91 ± 0.09). For non-experts, excessive bias (25° and 14°) was observed. An associated improvement in bias with additional measurement experience indicated a potential significant learning curve for interpreting these studies. Less inter-observer variability was observed between experts. CONCLUSIONS Measurement of TP is a reliable tool when used by experienced personnel, and their use as a preoperative tool should be reserved to ones with experience with such image assessments. Non-experts' measurements produced a weak agreement when compared to experts'.