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Objectives and questions: Computed tomography (CT) underpins modern three-dimensional (3D) planning in hip and knee arthroplasty, supporting implant positioning, alignment assessment, navigation, robotics, and patient-specific instrumentation. Despite widespread adoption, substantial variability exists in CT protocols, including inconsistent scan coverage, inclusion of key anatomical landmarks, variation in technical parameters and radiation dose. These inconsistencies may compromise planning accuracy and lead to repeat imaging. The aim of this study was to evaluate current CT protocols used for hip and knee arthroplasty planning and to propose consistent, best-practice guidelines through an informal consensus process.

Material and methods: A multidisciplinary team of orthopaedic surgeons, radiologists, engineers, medical physicists, and industry representatives reviewed 29 CT protocols (17 hip, 12 knee). Protocols were assessed for scan coverage, inclusion of anatomical landmarks, and technical parameters including tube voltage (kV), tube current (mAs), and use of metal artefact reduction strategies. Areas of overlap, inconsistency and omission were identified, and five harmonised CT protocols were developed through iterative discussion and informal consensus. Agreement was reached when participants confirmed the protocols reflected best clinical practice while meeting surgical planning requirements.

Results: Substantial variability was identified across existing CT protocols. Scan volumes were inconsistently defined, with 35% of hip protocols omitting the knee joint, which is required for assessment of leg length and femoral rotation. Key technical parameters such as kV and mAs were omitted in up to 65% of hip and 42% of knee protocols, and where reported, values varied widely (100–150 kV and 100–250 mAs for the hip protocols, and 90–140 kV and 120–400 mAs for the knee protocols). The consensus process resulted in five CT protocols. These defined clear scan boundaries, included essential anatomical landmarks, and specified consistent yet adaptable imaging parameters: Primary Hip: Pelvis, proximal femur, and both knees; 100 kV, 100 mAs. Revision Hip: Iliac crest to knee joint line; 140 kV, 140 mAs. Primary Knee: Hip joint (excluding full pelvis), both knees (~20 cm), and tibiotalar joint; 100 kV, 100 mAs. Revision Knee: Hip joint, both knees (~40 cm), and tibiotalar joint; 120 kV/120 mAs (knees) and 100 kV/100 mAs (hip and ankles). Total Femoral Replacement: Continuous scan from pelvis to ankles; 140 kV, 140 mAs.

Discussion and conclusions: This consensus study demonstrates significant inconsistencies in current CT imaging protocols for lower-limb arthroplasty planning. The proposed harmonised protocols provide clear, clinically focused guidance to optimise image quality, ensure inclusion of essential anatomical landmarks, and reduce unnecessary scan regions. Adoption of these protocols offer the potential to improve the reliability of CT-based planning, reduce repeat imaging, and enhance workflow consistency across hip and knee arthroplasty.