Inter-Observer and Intra-Observer Reliability of 2D Radiograph-Based Valgus Cut Angle Measurement in Preoperative Planning for Primary Total Knee Arthroplasty

Background Preoperative planning is imperative for a successful total knee replacement. Determining the valgus angle for the distal femoral cut from the preoperative 2D radiograph is a very inexpensive method that can be used to achieve the native knee alignment during a total knee arthroplasty (TKA). Objective The aim of this study was to document the intra-observer and inter-observer reliability of the valgus angle determination for distal femur cut from a preoperative digital radiograph in a TKA. Methods A total of 20 patients with bilateral grade 3-4 primary osteoarthritis were assessed independently by a medical student, five surgeons, of which one was a consultant with more than 20 years of experience, and four residents in varied levels of training. Full-length (pelvis to toes) weight-bearing radiographs of both lower limbs were obtained prior to the surgery. The measurements were made thrice at more than 24 hours interval without any possible knowledge of their own previous measurement or that of other surgeons. We assessed the angle between the mechanical and anatomical axis of both femurs. Results The single measures intraclass correlation was found to be 0.733, showing that there is a moderate reliability among the six raters when single measures were considered, whereas the average measures intraclass correlation was found to be 0.943, showing that there is an excellent reliability among the six raters when average measures were considered. For intra-observer reliability, the single measures intraclass correlation showed that there is a good-to-excellent reliability between the three trials when single measures was considered. The averages measures intraclass correlation showed that there is an excellent reliability between the three trials when average measures was considered. Conclusion A very inexpensive method of determining valgus angle for distal femur cut was found to have a moderate-to-excellent inter-observer reliability and a good-to-excellent intra-observer reliability.