Methodological aspects of the acromiohumeral distance measurement with ultrasonography—Reliability and effects of extrinsic and intrinsic factors in overhead and non‐overhead athletes

Abstract

Introduction: To improve comparability and interpretation of acromiohumeral distance (AHD) measurements, consequences of varying methodological approaches and population specific effects have to be known. This study aimed to investigate the intra-and inter-rater reliability of different AHD ultrasound image analysis approaches in asymptomatic overhead-and non-overhead athletes. Furthermore, the impact of shoulder muscle activity as well as relationships between AHD and individual factors were examined in different measurement positions.Methods: Isometric shoulder strength, shoulder range of motion (ROM) and AHD were measured in 27 male and female participants (14 overhead athletes; 13 nonoverhead athletes, age = 27.8 ± 5.2 years).Results: Intra-rater reliability (ICC 3,1 0.996) was excellent. Inter-rater reliability for the AHD defined as shortest distance between the most infero-lateral edge of the acromion and the most superior aspect of the humerus (ICC 2,1 0.997) was minimally higher than for the AHD defined as perpendicular distance (ICC 2,1 0.959). Increased shoulder muscle activity led to larger AHD reductions with abduction. Higher shoulder strength was associated with larger AHD, while larger shoulder ROM led to shorter AHD, dependent on measurement position and population. Conclusion:While shoulder muscle activity and ROM had a pronounced effect on AHD, effects of shoulder strength and population appeared to be marginal.