Systematic review for reliability and validity of ultrasound imaging for femoral cartilage morphology and composition against MRI: protocol.

INTRODUCTION: Evaluating femoral cartilage morphology (eg, thickness) and composition (eg, water content) is important for understanding and managing knee conditions including knee pain and osteoarthritis. While magnetic resonance imaging (MRI) is considered the reference standard for assessing cartilage morphology and composition, ultrasound imaging has gained increasing attention due to its affordability, accessibility and non-invasive nature. To date, the reliability and validity of ultrasound imaging for assessing femoral cartilage thickness and water content have not been thoroughly examined. This systematic review aims to evaluate the reliability and validity of ultrasound imaging for measuring femoral cartilage thickness and water content in individuals with and without knee pathology. METHODS AND ANALYSIS: This protocol for a systematic review and meta-analysis was developed in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) guidelines. PubMed (MEDLINE), EMBASE, Scopus, Web of Science and Cochrane Library will be searched for studies investigating the reliability and validity of ultrasound imaging for femoral cartilage thickness and water content. Studies published in English up to 1 April 2026 will be included. Risk of bias and methodological quality will be assessed using the COnsensus-based Standards for the Selection of Health Measurement Instruments checklist. Meta-analysis will be conducted when studies are sufficiently comparable in terms of population characteristics, imaging protocols and outcome definitions. ETHICS AND DISSEMINATION: Ethical approval is not required because this study will synthesise data from previously published literature. The findings will be disseminated through publication in a peer-reviewed journal related to orthopaedics, musculoskeletal imaging, or rehabilitation science, regardless of the results. PROSPERO REGISTRATION NUMBER: CRD420261352774.