Reliability of radiographic measurements of knee motion following knee arthroplasty for use in a virtual knee clinic

INTRODUCTION We sought to validate radiographic measurements of range of motion of the knee after arthroplasty as part of a new system of virtual clinics. METHODS The range of motion of 52 knees in 45 patients was obtained by 2 clinicians using standardised techniques and goniometers. Inter-rater reliability and intraclass correlation coefficients (ICCs) were calculated. Radiographs of these patients' knees in full active flexion and extension were also used to calculate intra and inter-rater reliability compared with clinical measurements using four different methods for plotting angles on the radiographs. RESULTS The ICC for inter-rater reliability using the goniometer was very high. The ICC was 0.91 in extension and 0.85 in flexion while repeatability was 8.49° (-8.03-8.99°) in extension and 5.23° (-4.54-5.74°) in flexion. The best ICC for radiographic measurement in extension was 0.86, indicating 'near perfect' agreement, and repeatability was 5.43° (-4.04- 6.12°). The best ICC in flexion was 0.95 and repeatability was 5.82° (-3.38-6.55°). The ICC for intrarater reliability was 0.98 for extension and 0.99 for flexion on radiographic measurements. CONCLUSIONS Validating the use of radiographs to reliably measure range of motion following knee arthroplasty has allowed us to set up a 'virtual knee clinic'. Combining validated questionnaires and radiographic measurement of range of motion, we aim to maintain high quality patient surveillance following knee arthroplasty, reduce our ratio for new to follow-up patients in line with Department of Health guidelines and improve patient satisfaction through reduced travel to hospital outpatients.