The modified Boytchev procedure, i.e., rerouting of the coracoid process with its attached conjoined tendon (short head of biceps and coracobrachialis) deep to the subscapularis and reattachment to its anatomical location, has been advocated for recurrent anterior glenohumeral instability with controversial clinical outcomes. We aimed to investigate the dynamic contribution of the conjoined tendon in situ or transferred to the glenohumeral articulation in stable and unstable shoulders. Eight cadaveric shoulders were tested with the arm in 90 degrees abduction and 90 degrees external rotation. A constant 1.5 kg anterior translation force was applied to the proximal humerus, combined with 0, 1.5, 3.0 kg of load applied to the conjoined tendon sequentially. Anterior displacement of the humeral head relative to the scapula was recorded before and after an imitation Bankart lesion was created, and after treated with the modified Boytchev procedure for the Bankart lesion. Application of load to the conjoined tendon significantly reduced anterior displacement of the humeral head either with the capsule intact or with Bankart lesion simulated. The most significant decrease of the anterior displacement occurred when the conjoined tendon was transferred beneath the subscapularis. Our findings show that the conjoined tendon per se has a stabilizing effect on stable and unstable shoulders and therefore provide scientific support for the treatment of recurrent shoulder instability using the modified Boytchev procedure.