Concurrent Validity and Test-Retest Reliability of Inertial Measurement Units for Measuring Spinal Kinematics: A Systematic Review

Background spine pain is a leading contributor to global pain and disability, and knowledge of spinal kinematics is essential for understanding and managing this pain and pathology. Expensive and laboratory-confined optoelectronic motion capture systems are considered the gold standard for joint angle measurement, but recently, small and inexpensive inertial measurement units (IMUs) have emerged as a promising alternative, and the rapid growth of literature in this area required a systematic review. Methods this systematic review aimed to compile and assess the current literature on concurrent validity (compared to gold standard optoelectronic systems) and test-retest reliability of IMUs for inter-segmental spine kinematics covering the trunk, lumbar, thoracic, and cervical regions into a unified framework in context of recently developed ISB guidelines. Three different databases (PubMed, Scopus, and Web of Science) were searched. Methodological quality was determined using a structured quality appraisal tool, while direction and strength of evidence were determined based on four criteria (imprecision, risk of bias, indirectness, and inconsistency). Results 37 studies met the eligibility criteria. Reported validity and reliability metrics indicate that IMUs have the potential to derive reliable and clinically valid spinal kinematics across all anatomical planes and regions. However, their performance is highly sensitive to variations in task, methodology, and context. Conclusions IMUs offer a promising and accessible alternative to optoelectronic systems, but their effective use requires careful consideration, specific validation, and adherence to standardized protocols.