Although back pain, neck pain, and headaches are the three most common reasons why individuals seek out the services of a chiropractor, shoulder pain is another frequent complaint seen in the office. Sometimes there is a traumatic mechanism to explain the onset of pain, such as a fall or over-exertion with lifting, reaching, pulling, or throwing types of activities. However, often the cause is not very obvious, suggesting that a more cumulative process has resulted in a pain experience at the shoulder. Discussing the structure and function of the shoulder will help us understand how this may occur. Note - it is also important to realize that pain felt at the shoulder may not have its origin at the shoulder at all but instead have a more central source, commonly the neck region, with structures either referring or radiating pain to the shoulder, with or without the presence of neck discomfort.
The shoulder is a ball and socket joint. As such, it is a very mobile joint with many movement possibilities, but with greater potential for instability as well. The "ball" is the head of the upper arm bone called the humerus and the "socket" is a shallow depression on the shoulder blade, made deeper only by the addition of projections of cartilage called the labrum. The shoulder blade essentially floats on our mid back by way of muscular attachments with its only direct bony connection to the rest of our skeleton being made via the collar bone. The four rotator cuff muscles attach the ball to the shoulder blade and function to keep the ball centred in the socket while larger muscles around the shoulder, the deltoid and "pecs" for example, create the actual movement of the shoulder/arm. With ranges of motion, the ball rotates and glides in the socket, the shoulder blade itself moves in a variety of directions, and the collar bone rotates and tilts. The mid back also needs to extend. All of these motions have a pre-wired sequencing or rhythm in which they occur to move the shoulder optimally and basically keep the ball in the socket. When this pattern of motion is altered due to a new injury or persists after an older problem resolved but wasn't fully rehabilitated, or simply as a result of postural imbalances, this sets the stage for future trouble.
Unlike other joints in the body where the muscles that move and/or stabilize the joint surround the bony connection, the shoulder is unique in that some soft tissues (i.e. rotator cuff muscles and tendons, bursae) are contained in an area surrounded by bony structures. To orient you, feel the bony tip of your shoulder blade, named the acromion, where the shoulder slopes down to become the arm. The area beneath the acromion is appropriately called the sub-acromial space, which houses those soft tissues, sandwiching them between the ball of the ball and socket below and the acromion above. If the rhythm mentioned previously becomes altered and the ball is not well maintained in the socket throughout ranges of motion, these tissues can become overly pinched, or "impinged" between the bony surfaces. Over time this can result in a number of different painful conditions, such as bursitis, a biceps tendonopathy, a rotator cuff tear or tendonopathy, shoulder impingement syndrome, and arthritis to name a few.
Part 2 of this article will continue this discussion and suggest a few things one may try to help optimize shoulder function. This article is for general information purposes only and is not to be taken as professional medical advice.