BACKGROUND: Lateral compression type1 (LC-1) fragility fractures are a common, painful injury in older adults resulting in reduced mobility. The incidence of these fractures is increasing with the growing older adult population. The current standard of care is non-surgical management; however, patients with this injury are at risk of long-term immobility and related complications. INFIX is a pelvic fixation device used in younger patients with high-energy fractures. The device is fitted via a percutaneous technique with no external pin sites and has good purchase even in osteoporotic bone. It therefore has the potential to be well tolerated in patients with LC-1 fragility fractures. INFIX could improve patients' ability to mobilise and reduce the risk of immobility-related complications. However, there is a risk of complications related to surgery, and robust evidence is required on patient outcomes. This study will investigate the clinical and cost-effectiveness of surgical fixation with INFIX compared to non-surgical management of LC-1 fragility fractures in older adults. METHODS: A multi-centre randomised controlled trial of 600 patients allocated 1:1 to non-surgical management or INFIX surgery. The study will have a 12-month internal pilot to assess recruitment and trial feasibility. The primary outcome will be the patient quality of life over 6 months, measured by the patient-reported EQ-5D-5L. The secondary outcomes will include physical function, mental health, pain, delirium, imaging assessment, resource use, and complications. DISCUSSION: The L1FE study aims to compare the clinical and cost-effectiveness of surgical and non-surgical management of people aged 60 years and older with LC-1 fragility fractures. The trial is sufficiently powered and rigorously designed to inform future clinical and patient decision-making and allocation of NHS resources. TRIAL REGISTRATION: International Standard Randomised Controlled Trial Number Registry ISRCTN16478561. Registered on 8 April 2019.