Report (Requirement #2)
By Bop DiBenedetto
Near the beginning of IRC, I started experiencing shoulder pain and learned I had a slightly non-functioning/activating serratus anterior. Rehabbing my shoulder, being hypermobile, along with learning that I had little to no clue what the scapulothoracic joint actually did (or was) lead me to wanting to learn more about the scapulothoracic joint and how it glides around the thorax. This paper is an examination of the structures within the scapulothoracic joint, more specifically the layers from the scapula to the ribs (or the scapulothoracic joint sandwich as I visualize it-the bony structures are the bread, it makes more sense if you look at pictures of MRIs).
The scapulothoracic joint is a false joint. Joints are characterized by fibrous, cartilaginous, or synovial tissue attachments to another bony structure[1]. The scapula is attached to the thorax by ligaments at the acromioclavicular joint, and suction provided by muscular attachments. The lack of bony attachments allows a wide range of movement[2]. The scapulae are separated from the ribs by: 2 muscles-the serratus anterior, and the subscapularis; 2 main bursae (not attached to any bony structure)-the scapulothoracic bursa, and the subscapularis bursa; and fascia-allowing for smooth gliding of the scapulae over the ribs and musculature[3]. Any movement of the scapula on the thorax is accompanied by movement of the acromioclavicular or sternoclavicular joints[4] (which is something I will not be covering in this paper).
The serratus anterior can be broken into three parts: the superior, middle, and inferior part. All 3 parts originate on the lateral side of the thorax, under the pectoral muscles. The superior part begins at ribs 1 to 2, and attaches to the superior angle of the scapula. The intermediate part begins at ribs 2 to 3 and attach to the medial border of the scapula. The inferior part begins at ribs 4 to 9 and attach to the medial inferior angle of the scapula. The inferior part is the most prominent and powerful. Beyond providing stabilization during shoulder elevation, and protraction, the serratus anterior lifts the ribs during respiration, and the inferior and superior parts act antagonistically for stabilization[5]. For example, when elevating your arm or inhaling, the inferior part allows the scapula to glide ventrolaterally around the ribs, while the superior part depresses the scapula, maintaining the suction of the scapula to the thorax.
Interesting (and slightly off-topic) tidbit about the serratus anterior: due to the movements controlled by this muscle (and the average person’s daily activities), a person using crutches often feels side pain. When a person is injured and needs to use crutches, they often feel like the crutches are rubbing against the side of their body and causing pain. The pain they experience is usually muscle soreness, due to the average person’s movement patterns not engaging the serratus anterior, rather than chafing.
The subscapularis is the largest muscle of the rotator cuff. It originates on the anterior surface of the scapula-more specifically the medial and lower two thirds groove on the lateral border[6]. The subscapularis attachment is complex. The muscle transitions to a tendon, with three distinct sections with different attachment areas. The superior part blends with the ‘biceps pulley system’, the middle part attaches to the lesser tuberosity, while the lower part is a less common muscular attachment to the lesser tuberosity of the proximal humerus[7]. It important in stabilizing the glenohumeral joint, internally rotating and adducting the humerus, and promotes coordination between the glenohumeral and scapulothoracic joints[8]
Bursae are tiny fluid filled sacs that allow gliding between structures throughout the body. Bursa are comprised of a very thin synovial membrane which surrounds (and produces) synovial fluid-which is lubricating fluid for the joint (like joint WD-40). Bursae are divided into 3 types: synovial, superficial, and adventitious/accidental. Synovial bursae are located between bones and muscles, tendons, and ligaments. Superficial bursae are located just below the skin. Adventitious bursae develop when repeated irritation occurs[9]. The scapulothoracic joint contains 2 synovial bursae and around 4 adventitious bursae. The scapulothoracic (or infraserratus) bursa is located between the serratus anterior and the chest wall. The subscapularis (or supraserratus) bursa is located between the subscapularis and serratus anterior muscles[10]. The minor 4 bursae (adventitious), when found, are scattered around the inferior margin of the scapula[11],[12].
Fascia is a multi-layer tissue, with liquid (hyaluronan) between the layers. It surrounds every organ, blood vessel, bone, nerve fiber, and muscle, and keeps them in place[13]. Fascia has 3 fundamental structures: superficial, deep, and muscle related layers. Superficial fascia is comprised of loose connective tissue containing webs of collagen and some fibers of elastin. Deep fascia is formed by a connective membrane that is devoid of fat and sheaths all muscles, nerves, vessels, and various organs and glands. The Muscle-related layers is the fascia that encloses each muscle and is involved with the tension between the muscle spindles and Golgi tendon organs[14].
Focus on the scapula as a solution and cause for shoulder pain is relatively new (within the past 25-ish years). The scapula itself has 17 muscles that attach to or originate from it and is massively important in stabilization and assisting in wider range of movement in the shoulder (lifting the arm overhead would not be possible without it). While it’s easy to say that a specific muscle does one thing (like serratus anterior responsible for punching), a whole complex of muscles must work in concert to make a movement possible and stable (video with muscle pulling elves on Scapular Force Couple demonstrating this). To sum up the anatomy of the scapulothoracic joint in sandwich-layer terms: scapula-> subscapularis->bursa(e)->serratus anterior->bursa->ribs, with fascia surrounding the structures, and ligaments connecting muscles to the bones.
Understanding joint movements and anatomy is helpful for my own movement, awareness, and knowledge; and by extension my ability to coach. Awareness of one’s own body can be learned a myriad of ways, through movement, tactile and verbal cueing, knowledge of anatomy, and more. People learn different ways, my ability to explain what I’m asking them to do, and understanding what they are actually asking me, is greatly improved if I have knowledge of the body and its mechanics. Since this research, I have already found myself more aware of my scapulothoracic joints, what muscles are activating, and what structures are gliding over each other each time I do conditioning or rehab exercises.
[1] Physiopedia: Scapulothoracic Joint
[2] Paine, Russ, and Michael L Voight. “The role of the scapula.” International journal of sports physical therapy vol. 8,5 (2013): 617-29.
[3] Medscape: Scapulothoracic Joint Pathology
[4] "Scapulothoracic Joint." Physiopedia, . 29 Aug 2019, 19:53 UTC.
[5] KenHub: Serratus Anterior Muscle
[6] Aguirre K, Mudreac A, Kiel J. Anatomy, Shoulder and Upper Limb, Subscapularis Muscle. [Updated 2021 Aug 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.
[7] Sports Injury Bulletin: As the shoulder turns: understanding the subscapularis-Part 1
[8] KenHub: Subscapularis Muscle
[9] Arthritis-health: What is a Bursa?
[10] Merolla G, Cerciello S, Paladini P, Porcellini G. Snapping scapula syndrome: current concepts review in conservative and surgical treatment. Muscles Ligaments Tendons J. 2013 Jul 9;3(2):80-90. doi: 10.11138/mltj/2013.3.2.080. PMID: 23888290; PMCID: PMC3711706.
[11] Acar N. Low-energy versus middle-energy extracorporeal shockwave therapy for the treatment of snapping scapula bursitis. Pak J Med Sci. 2017 Mar-Apr;33(2):335-340. doi: 10.12669/pjms.332.12262. PMID: 28523033; PMCID: PMC5432700.
[12] Frank RM, Ramirez J, Chalmers PN, McCormick FM, Romeo AA. Scapulothoracic anatomy and snapping scapula syndrome. Anat Res Int. 2013;2013:635628. doi: 10.1155/2013/635628. Epub 2013 Nov 28. PMID: 24369502; PMCID: PMC3863500.
[13] John’s Hopkins Medicine: Muscle Pain: It May Actually Be Your Fascia
[14] Thomas Findley, Hans Chaudhry, Antonio Stecco, Max Roman, Fascia research – A narrative review, Journal of Bodywork and Movement Therapies, Volume 16, Issue 1,2012,Pages 67-75,ISSN 1360-8592