The influence of bicipital groove morphology on the stability of the long head of the biceps tendon.

Purpose: We aimed to evaluate the influence of the bony morphology of the bicipital groove on the stability of the long head of the biceps tendon (LHBT).

Methods: Among the patients who underwent magnetic resonance imaging of the shoulder at our outpatient clinic in 2012, those aged >40 years were included. After excluding cases with complete tear or unclear positioning of the biceps tendon, 464 shoulders were analyzed according to the position of the LHBT with respect to the bicipital groove. Shoulders with subluxation or dislocation of the LHBT were labeled as having unstable LHBT, while those with the LHBT located in the bicipital groove were labeled as having stable LHBT. The bony morphology of the bicipital groove was measured in terms of opening angle, medial wall angle, and depth. A shallow bicipital groove was defined as having an opening angle >94°, concurrent with earlier studies. We compared shoulders with stable and unstable LHBT regarding bicipital bony morphology. We also compared shoulders with normal and shallow grooves regarding tendon stability.

Results: Shoulders with stable and unstable LHBT differed significantly regarding bony morphology. Shoulders with unstable LHBT showed a shallower mean depth (by 0.3 mm; p = 0.008), a smaller mean medial angle (by 2.2°; p = 0.014), and a larger mean opening angle (by 3.7°; p = 0.016). Bony morphology characterized by a shallow groove was significantly associated with increased prevalence of instability defined as LHBT subluxation or dislocation ( p = 0.011).

Conclusion: A shallow bicipital groove, identified by the larger opening angle, smaller medial angle, and shallower depth, may represent a predisposing factor for biceps tendon instability.