Abstract. Background. Lower limb mechanical axis has long been seen as a key to successful in lower limb surgery, including knee arthroplasty. Traditionally, coronal alignment has been assessed with weight-bearing lower limb radiographs (LLR) allowing assessment of hip-knee-ankle alignment. More recently CT scanograms (CTS) have been advocated as a possible alternative, having the potential benefits of being quicker, cheaper, requiring less specialist equipment and being non-weightbearing. Objectives. To evaluate the accuracy and comparability of lower limb alignment values derived from LLR versus CTS. Methods. We prospectively investigated patients undergoing knee arthroplasty with preoperative and postoperative LLR and CTS, analysing both preoperative and postoperative LLRs & CTS giving 140 imaging tests for direct comparison. We used two independent observers to calculate on each of imaging modalities, on both pre- and post-operative images, the: hip-knee-ankle alignment (HKA),