Moment arms of the coracobrachialis and short head of biceps following a Latarjet procedure: a modeling study

Abstract

BackgroundThe Latarjet procedure transfers the coracoid process to the anterior glenoid. This prevents recurrent anterior humeral dislocation but alters the origin of the coracobrachialis (CBR) and short head of bicep (SHB). The impact of this alteration on the moment arms of these muscles has not been examined. MethodsThe Newcastle Shoulder Model was updated with 15 heathy cadaveric bone models to create customized shoulder models. The CBR and SHB muscles were attached to the anterior glenoid via an elliptical wrapping object. Muscle moment arms were calculated for abduction, forward flexion, scapula plane elevation and internal rotation with 20⁰ and 90⁰ abduction. Statistical comparison between native and Latarjet moment arms was performed using spm1D. ResultsBy transferring the origin of CBR and SHB to the anterior glenoid, both muscles had extension moment arms during glenohumeral elevation in coronal, sagittal, and scapular plane. Their average moment arms during abduction (CBR: -30.4±3.2mm; SHB: -29.8±3.0mm) and forward flexion (CBR: -26.0±3.1mm; SHB: -26.2±3.2mm) suggested that their role after Latarjet changed, compared with that of their role in a native shoulder (p<0.001). At higher abduction levels both the muscles had higher internal rotation moment arms compared to the native shoulder. ConclusionThe Latarjet procedure affected the moment arms of the CBR and SHB. Both muscles had increased extension and internal rotation moment arms at higher degrees of elevation, compared to the native shoulders, this suggests that these muscles act as dynamic stabilizers after Latarjet.