Objectives: To establish the reliability of a standardised ultrasound protocol to measure normal inferior glenohumeral capsule (IGHC) thickness and to investigate the effects of age, sex, hand dominance and angles of abduction on the thickness.
Methods: IGHC images were obtained at 60o, 90o and 180o abduction angles of 151 asymptomatic shoulders in supine position. Following the proposed guidelines, three sonographers blindly measured the IGHC thicknesses for intra- and interrater reliability assessments.
Results: The intrarater reliability was excellent (intraclass correlation coefficient value = 0.95; 95% CI = 0.92-0.97). The interrater reliability was moderate (intraclass correlation coefficient value = 0.74; 95% CI = 0.60-0.83). The mean IGHC thickness values in mm ± SD at 60o, 90o and 180o abduction angles for males were 3.3 ± 0.93, 3.0 ± 0.80 and 2.6 ± 0.55 and those for females were 2.7 ± 0.86, 2.4 ± 0.7 and 2.0 ± 0.56 respectively. Although males had thicker IGHC, the rate at which the thickness reduced with increased abduction was same in both males and females. Age and hand dominance had no effect.
Conclusion: The normal IGHC thickness varies with sex and the abduction angle of the arm at which it is measured. A large variation of IGHC thickness exists in the normal population.
Advances in knowledge: The results of this study discourage the use of a single value of IGHC thickness and emphasise the importance of comparing the thickness of the symptomatic side to that of the asymptomatic side of the same subject at the same abduction level. The guidelines provided in this study can be used in clinical practice and in future research studies.