Role of deltoid and passives elements in stabilization during abduction motion (0 degrees-40 degrees): an ex vivo study.

The deltoid and the passive elements of the glenohumeral joint play a role during abduction of the upper limb. However, there is a lack of quantification of their respective role. The aim of the present study was to describe the influence of the deltoid and the passive elements during kinematics experiments in abduction (0 degrees-40 degrees) of unconstrained humerus. Six fresh-frozen anatomical specimens were considered. Bi-planar X-rays were obtained using the EOS imaging system (Biospace Med, Paris, France). Then a horizontal traction at constant speed was applied to the "acromion and clavicle block", using an universal testing machine and specific device, and the humerus kinematics was recorded using an optoelectronic system (Polaris, NDI, Canada). For each anatomical specimen the protocol included two types of tests: intact capsule and perforated capsule. For a displacement of 28 mm of the acromio-clavicular set, the amplitudes of "abduction" rotation vary between 26 degrees and 41 degrees for the "intact capsule" configuration and between 27 degrees and 40.5 degrees for injured capsule configuration. For the same displacement the translation according to Y of the humeral head changes between 1 and 5.5 mm for intact capsule configuration and between -0.5 and 5.5 mm for injured capsule configuration. During the abduction (0 degrees-40 degrees) motion this study suggests that the humeral head is stabilized by the deltoid, the labrum, tendons of the rotators cuff and to a lesser level by the glenoid.