Acromiohumeral Distance as a Diagnostic and Prognostic Biomarker for Shoulder Disorders: A Systematic...

Objectives: The acromiohumeral distance (AHD) is widely used to evaluate subacromial pathology, particularly rotator cuff-related disorders. However, substantial heterogeneity exists across studies in imaging protocols, measurement definitions, and diagnostic thresholds. This systematic review aimed to synthesize current evidence on AHD measurement methods, assess reliability and diagnostic performance across imaging modalities, and examine the clinical relevance of AHD as both a structural and functional biomarker. Methods: A systematic search of PubMed, Web of Science, and SciELO (January 2006-May 2025) was conducted following PRISMA 2020. Eligible studies reported quantitative AHD measurements using ultrasound, MRI, or radiography in adults. Two reviewers independently conducted screening, extraction, and QUADAS-2 assessments. Due to heterogeneity, results were narratively synthesized. Results: Twenty-nine studies met the inclusion criteria. Definitions of AHD and imaging procedures varied substantially. Ultrasound showed the most consistent intra- and inter-observer reliability, whereas MRI and radiography demonstrated greater protocol-dependent variability. Reduced AHD values were frequently associated with full-thickness rotator cuff tears, while larger values typically characterized asymptomatic individuals. Several studies also reported reductions in AHD during arm elevation, supporting its interpretation as a functional parameter influenced by scapular motion and neuromuscular control. Conclusions: AHD is a reliable and clinically informative measure when acquired using standardized protocols, with Ultrasound demonstrating the highest reproducibility. Its sensitivity to positional and dynamic factors supports its role as both a structural and functional biomarker. Further research should prioritize standardized imaging procedures, dynamic assessment methods, and evaluation of emerging technologies to improve the diagnostic and prognostic value of AHD.