Prospective, observational study to evaluate the relation between patient-reported outcomes and component rotation in total knee replacement: protocol for the CRACK study

INTRODUCTION: Total knee replacement (TKR) for osteoarthritis results in a satisfactory outcome in the majority of patients, although up to one in five patients may be dissatisfied with the outcome. Persistent pain is a main contributor to patient dissatisfaction, and femoral and tibial component malrotation have been identified as a potential cause for both persistent pain and patellofemoral problems. Based on the assumption that component malrotation is the causative factor for persistent pain, early revision for patients with symptomatic malrotated components has been advocated in the literature. However, convincing evidence that component malrotation indeed results in less than optimal outcomes is lacking. This study aims to assess the relation between knee prosthesis component rotation and patient-reported outcomes in a large group of patients and to determine the range of femoral, tibial and combined rotation that results in the best clinical outcomes. METHODS AND ANALYSIS: In this single-centre, prospective observational cohort study, a total of 500 patients will undergo TKR. All patients will have a 3D-CT assessment of femoral and tibial component rotation within 8 weeks after surgery. Outcome measures will include the Oxford Knee Score, the Knee Injury and Osteoarthritis Outcome Score, EQ-5D, visual analogue scale for pain, the American Knee Society Score and the knee joint range of motion. We will assess the relation between femoral, tibial and combined component rotation and patient-reported outcome measures at 8 weeks and 1 year of follow-up, and we will determine the range of femoral, tibial and combined rotation that results in the best clinical outcomes. ETHICS AND DISSEMINATION: Ethical approval for this study has been granted by the Isala Hospital ethics committee. The results will be published in a peer-reviewed journal and presented at relevant meetings. TRIAL REGISTRATION NUMBER: NL7635.