The role of atmospheric pressure in stabilising the shoulder. An experimental study

The role of atmospheric pressure in providing static stability of the shoulder was studied experimentally in 24 cadaveric shoulders. Atmospheric air was allowed to enter the joint after puncturing the capsule. Three types of experiment were performed: in the first, the capsule was punctured after sequential division of the muscles; in the second, atmospheric air was let in by percutaneous puncture of of the capsule without dividing the muscles; and in the third, air was first let into the joint by percutaneous puncture of the capsule and then the muscles of the shoulder were divided. It was found that the intact shoulder subluxated after percutaneous puncture even without division of the overlying muscles or the capsule. Our findings suggest that negative pressure and muscle tone are the main static stabilisers of the shoulder, rather than the joint capsule.