Monday, June 15, 2009
Anatomy of the Shoulder and Rotator Cuff
I have received an inordinate number of calls this week from attorneys with rotator cuff injury cases or medical malpractice cases involving arthroscopic shoulder repairs. Regretfully, many of these conversations have reinforced my opinion that the shoulder is one of the most widely misunderstood areas of anatomy that is frequently involved in litigation. To many attorneys this ball and socket joint seems like a confusing mass of tendons and skeletal structures with functions that are difficult to recognize and names that are hard to pronounce. It certainly doesn’t need to be that hard. I’ll take just a few minutes to provide a basic overview of the anatomy of the shoulder so that you’ll be better prepared in your next personal injury or medial malpractice case.
In my opinion, the key to understanding the entire shoulder is a thorough understanding of the scapula (shoulder blade). The scapula is a fairly flat triangular shaped bone located on the upper outer portion of the back. The back of the scapula is divided by a ridge called the spine that we will be important to remember later when we discuss the rotator cuff. You should also note the two small projections or processes that protrude from the scapula. The tip of the spine becomes the acromion process projecting upward which articulates with the clavicle (collar bone). Also there is the coracoid process that projects forward.
Both of these processes provide attachments to various muscles of the chest and arm. The final skeletal aspect of the scapula that you need to appreciate is the glenoid cavity that forms the socket portion of the ball and socket joint of the shoulder.
The rotator cuff is a group of four muscles that that extend from the scapula to the humerus (upper arm bone) to provide stability and prevent dislocation. The first three of these muscles are named in association with where they lie in relation to the scapula. Now that you appreciate the skeletal anatomy of the scapula, you will better understand these names. The supraspinatus runs along the top of the scapula above the spine. The infraspinatus runs along the back of the scapula beneath the spine. The subscapularis runs beneath the scapula. There is also the teres minor which runs on the back of the scapula at the very bottom. Any or all of these muscles or the tendons that connect them to the humerus can be injured, but in my experience, the supraspinatus is by far the most commonly injured. One reason for the vulnerability of the supraspinatus is that it runs beneath the acromioclavicular joint where the clavicle joins the acromion process. Injury to either surface of this joint can cause bone spurs that protrude down leading to tearing of the underlying supraspinatus tendon.
Of course there are other aspects of the shoulder that I haven’t discussed here such as the glenoid labrum, the subacromial bursa, the vessels of the thoracic outlet or the nerves of the brachial plexus. Perhaps we will return to the shoulder in future articles and explore this wonderfully complex joint in greater detail.