Background:The hourglass biceps, an intra-articular entrapment of the long head of the biceps (LHB), is a possible diagnosis in cases of shoulder pain associated with loss of passive elevation.Purpose:The objective of this study is to investigate the role of dynamic ultrasound (U/S) in determining the diagnosis of the hourglass biceps lesion.Materials and Methods:A prospective cohort of 16 patients with the clinical suspicion of an hourglass lesion, a preoperative ultrasound, and a confirmed hourglass LHB at surgery, were included in the study. Eight patients had preoperative dynamic ultrasound assessment of the LHB, and eight had standard ultrasound investigations and served as a control group.Results:Dynamic ultrasound accurately diagnosed an hourglass biceps in three out of eight cases. LHB hypertrophy was demonstrated in five out of eight cases with U/S and three out of eight cases with standard U/S. All patients were treated by excision of the intra-articular portion of the LHB, 15 by bipolar tenotomy, and one by LHB tenodesis.Conclusions:Dynamic ultrasound shows promise in improving the accuracy in diagnosis of LHB hypertrophy and the Hourglass lesion.Level of Evidence:III (Consecutive case-control study investigating a diagnostic test).