The shoulder should not be placed at 90 degrees to the mattress as this may trigger spasm in the trapezius muscle. The trapezius muscles perform a variety of actions, including acting as a platform for elevating the skull and need to recover during sleep. If the shoulder is placed slightly forward on the mattress, in front of the sleeper, assuming the mattress can accommodate this position, the risk of forcing the scapula towards the spine is reduced. When positioned in the 90 degree position sleepers may wake with upper arm pain and sensation to the little and ring fingers. If a pillow applies excessive pressure to the neck in the back sleeping position, particularly the C2, C3, vertebrae, then treatment that has been provided will almost always be compromised.
Pressure can irritate the nerve sheaths, sensitive muscles, and facet joints in the neck.
Equally, if the joints are not resting easy, the inflammatory process may be sustained and any recovery will be much more difficult. The nerve pathway at this site travels down the arm, and causes either upper arm pain or pins and needles in the little and ring fingers or both, especially if there is already a problem in this area. Many shoulder problems are caused by referred pain from the neck, therefore, stabilising the neck during sleep is of paramount importance. The skull is, in the main, held up by the shoulder muscles, therefore any compromising of these muscles during sleep will generally not be solved by a pillow, if the shoulders are being compressed for long periods. A question asked by so many.