For this project, we were tasked with creating our own improved joint in order to alleviate the commonality of a certain dysfunction or injury. I chose the shoulder joint, in particular the dislocation of the glenohumeral joint, because I was curious about the specifics of how dislocation works, as I have never personally had it happen to me before. I had also recently come across a certain dysfunction of the body that intrigued me, the Ehlers-Danlos Syndromes(EDS) which also pertains to dislocation, motivating me to chose this topic. Throughout the project, I researched the anatomy of the shoulder, finding important structures crucial to the movements of the shoulder, and then looked up what exactly causes the dislocation of the shoulder. In doing so, I realized the broad nature of the term “dislocation of the shoulder” and narrowed it down to a more specific injury in a Bankart lesion. I then brainstormed a way to fix the problem, and recorded the details of my discoveries down below.
The shoulder joint is the joint that I focused on for this project, and it is actually composed of 4 joints, only one of which I centered on for my project. The glenohumeral joint is the typical ball-and-socket joint that connects the humerus and the scapula at the glenoid cavity when one thinks “shoulder”, and the joint is stabilized by surrounding rotator cuff muscles and glenohumeral ligaments. Specifically, the superior, inferior, and middle glenohumeral ligaments(GHL) help keep the shoulder from dislocating, while the coraco-aromial ligament(CAL) links the corocoid process, a part of the scapula which projects, to the acromion, the notable ridge on the clavicle. Another ligament is the coraco-clavicular ligament, which works to connect the scapula and the clavicle. The shoulder has two main types of tendons: the rotator cuff tendons, a group of four tendons including the scapularis, supraspinatus, infraspinatus, and teres minor; and the biceps tendons, having both the long and short head tendons to connect the bicep to the shoulder. Nerves of the shoulder are called the brachial plexus, and include the axillary nerve, long thoracic nerve, suprascapular nerve, musculocutaneous nerve, and many more. Blood vessels that surround the shoulder joint include the subclavian and axillary veins and arteries.
As mentioned before, the shoulder joint is a ball-and-socket joint, and is given some stability by the glenoid labrum, a fibro-cartilaginous surrounding of the glenoid cavity which also fuses the two parts of the joint together. The rotator cuff tendons and their attached deep muscles, as the name may suggest, rotates and extends at the shoulder joint, allowing us to circumduct our shoulders. Additionally, muscles that elevate, depress, and rotate the scapula and the clavicle, two other bones along with the humerus that make up the shoulder joint, include the trapezius, rhomboid major, and pectoralis minor, to name a few.
Despite the placement of many of these structures intended to stabilize the shoulder joint, the fact that the humerus does not completely fit into the glenoid cavity makes the joint susceptible to instability, which can result in the injury of shoulder dislocation. Shoulder dislocation can be classified as being caused traumatically(with the joint being knocked out of normal position with excessive force) or atraumatically(either habitually or painlessly, usually occurring without as much force). Considering that this project deals with the improvement of what structures are involved within the joint and not so much with the muscles surrounding the joint or the problems of individuals having more “lax” joints(associated with hyperextension, etc), I chose to focus on the traumatic dislocation of the shoulder, specifically the injury of a Bankart lesion.
The chance of dislocation is exponentially increased when there is instability in the shoulder, caused by a tear or distortion of the glenoid labrum and/or the glenohumeral ligaments mentioned above. For traumatic dislocation especially, the most common injury is called the Bankart lesion, where a part of the glenoid labrum is torn from the bone. In order to prevent this injury from happening, or at least lessen the severity of it, my proposal of a better joint would be either to increase the thickness of the labrum by 1 mm. The labrum as it is currently is 3.8mm’ 3.3 at the subscapularis bursa level, and 6.1mm’ 5.8 at the inferior portion of the glenoid, so adding on an additional 1 mm or so would greatly increase the durability of the labrum, but might cause problems with flexibility of the shoulder, in rotation or extension of the arm.
Another proposal would be to add a new structure to the inside of the labrum, in between it and the glenoid, to help hold the labrum to the glenoid and the bone with more stability. The labrum would have that additional structure holding it to the glenoid to prevent it from tearing as easily; however, the addition of that intermediate structure may affect the way the humerus fits into the scapula, and perhaps cause the glenohumeral joint to pop in and out even more easily, perhaps causing atraumatic dislocation of the shoulder. Since there are no major blood vessels weaving within the joint, those would remain unaffected, but the rotator cuff tendons that surround the glenohumeral joint may be stretched with the extra tissue inside the joint, and the stability provided by the glenohumeral ligaments(superior, inferior, and middle) may also be compromised with with this addition.
For both of these designs, I was inspired by looking at a diagram of the glenoid labrum and thought logically of how I could bolster the natural design of joint. I realized that since the labrum itself is reminiscent of the meniscus of the knee, and overall is just a rim of fibrous tissue, a thickening of the tissue might help with preventing tears; consequently, the observation that the labrum and glenoid had nothing in between the area that usually gets the most torn led me to the conclusion that something should be done to patch the area together. My design does have its flaws though; I mentioned how the surrounding ligaments and tendons and even the joint itself might be taxed by my alterations, but the nervous system may well be affected as well. The suprascapular nerve does branch down close to the glenohumeral joint, so if the glenoid cavity were to be lessened somewhat, the nerve itself may become entrapped.
Obviously, since we are unable to truly “fix” our joints, proper care of these problem areas and building strength in the muscles surrounding it are the only ways we can prevent these injuries from happening. For traumatic shoulder dislocations, prevention can be found in avoiding high-contact sports and being careful of harshly impacting the shoulder, while we can minimize damage by exercising the shoulder muscles to increase the cushion that we have when falling; atraumatic shoulder dislocations can be relieved through exercises and surgery to some extent.
Works Cited
"Bones and Joints of the Shoulder." ShoulderDoc. N.p., 11 Feb. 2016. Web. 27 Apr. 2017.
"Glenoid Labrum." ShoulderDoc. N.p., 5 Mar. 2017. Web. 05 May 2017.
"Labrum." ShoulderDoc. N.p., 7 May 2017. Web. 09 May 2017.
National Institute Of Arthritis And Musculoskeletal And Skin Diseases. The human shoulder joint. Digital image. Wikimedia Commons. N.p., 16 Sept. 2006. Web. 8 May 2017.
"Nerves of the Shoulder." ShoulderDoc. N.p., 7 May 2017. Web. 08 May 2017.
"Shoulder Anatomy." Arthritis Foundation. Arthritis Foundation, n.d. Web. 27 Apr. 2017.
"Shoulder Dislocation." ShoulderDoc. N.p., 5 Feb. 2017. Web. 05 May 2017.
"Shoulder Ligaments." ShoulderDoc. N.p., 5 Mar. 2017. Web. 05 May 2017.
Totora, Gerard J., and Bryan Derrickson. Introduction to the Human Body. 7th ed. New York: John Wiley and Sons, 2007. Print.
Weinstock, David. Shoulder Injury. Digital image. Flickr. N.p., 17 Sept. 2016. Web. 9 May 2017.
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