CT protocols for lower limb arthroplasty: the Stanmore hip and knee protocols

Computed tomography (CT) enables 3D surgical planning for implant size and position, patient-specific instruments, and robotic-assisted lower limb joint replacement. Orthopaedic companies provide CT protocols tailored to specific implant systems and designs, including off-the-shelf and custom-made implants, leading to substantial variability in imaging guidelines for centres and hospitals. This study aims to consolidate CT imaging workflows through harmonised protocols that minimise ambiguity and enhance clarity, clinical practice and patient safety. A multidisciplinary team critically reviewed all 17 hip and 12 knee CT protocols that were available. Imaging elements were assessed, highlighting deficiencies and inconsistencies. These protocols informed the recommendation of five harmonised CT protocols through informal consensus: i) primary hip, ii) revision hip, iii) primary knee, iv) revision knee and v) total femoral replacement. Significant variability was found among company guidelines regarding scan volume, X-ray tube current, voltage and other parameters, resulting in inconsistent image quality and radiation exposure. Lack of harmonisation can lead to scan rejections and repeat imaging. The harmonised protocols prioritise high-resolution imaging with optimal parameters, reduced scan volume and minimal metal artefacts. Designed to be clear, concise, consistent and comprehensive, these user-friendly protocols effectively capture key anatomical structures, landmarks and alignment details crucial for planning and monitoring lower limb arthroplasty. The protocols are sufficiently flexible to accommodate both standard and customised implant planning requirements. These protocols streamline the imaging process, fostering alignment across companies by consolidating existing protocols; they reduce duplication and eliminate inconsistencies, without redefining the content or intent of the original protocols.