Bursa: Not a Vestigial Organ
A seemingly useless tissue was
often surgically removed until it
was found to be very important
by Jerry Bergman, PhD
One of my favorite topics to research is vestigial organs. My guiding supposition is the human body was created, and did not evolve. Thus claims of vestigial (i.e., useless or worse than useless) organs have time and time again been proven to be incorrect.
Vestigial organs are defined as rudimentary organs (the term Darwin used), anatomically defined as “structures that are retained in a species despite having lost their primary ancestral function. These structures often lack an apparent purpose, in contrast to the full functionality of these organs observed in closely related and ancestral species.”[1] Synonyms of vestigial organs include degenerated organs, or remnant organs. As long ago as 1964 it was recognized that an organ labeled vestigial “may have a function which has not been discovered.” [2] Over and over this has been proven to be the case.
As a result of researching this topic for the last 30 years, I have learned by a detailed study of the peer-reviewed, scientific literature that all of the claimed vestigial organs have been proven by empirical research to be useful. Many have one or more very important functions.[3] Thus, I have seen the vestigial claim go from 100 claimed examples to none.
One claimed vestigial organ I was unaware of was the bursa tissue in the shoulder. When teaching anatomy, I explained that the bursa is a thin, fluid-filled sac whose sole role was to protect the tendons by providing a cushion between the tendons and adjacent bones. Now we have good evidence that it does much more than this. I was unaware of the bursa example which was described by one anatomist as “an unimportant vestigial structure.”[4] Other anatomists even describe the ligament that is located near the bursa, the coracohumeral ligament, as also a vestigial remnant of the humeral insertion of the pectoralis minor.”[5]
The Main Bursa
Figure 1. Note the bursa in blue. From Wikimedia Commons.
Actually, only the main bursa of the shoulder, which facilitates normal movement, has been studied in depth, partly because it is commonly the bursa involved in certain shoulder disorders (see Figure 1). Of note is, the “other shoulder bursae have been described, but their anatomy has not been well studied.” [6]
This again illustrates our lack of complete knowledge about our own bodies. If an organ is thought to be vestigial, the reasoning goes, it can be removed without problems. Now new evidence has determined that a “common practice of shoulder surgeons may be impairing the success of rotator cuff surgery, [according to] a new study from orthopedic scientists and biomedical engineers at Columbia University.[7] This practice is the removal of the main bursa.
In the past, surgeons often removed “the bursa while repairing torn tendons in the shoulder joint, but the Columbia University study suggests that this small tissue plays a role in helping the shoulder heal.”[8] The bursa removal was done in spite of the fact that anatomists “don’t know the role of the bursa in rotator cuff disease, so we don’t know the full implications of removing it.”[9] This will likely change because the Columbia University research supports the view “that surgeons should not remove the bursa without carefully considering the consequences.”[10]
Figure 2. Note the supraspinatus muscle. From Wikimedia Commons.
The scientists used an animal model with rats to evaluate the function of the bursa. They performed supraspinatus (i.e., the muscle of the back of the shoulder that arises from the supraspinous fossa of the scapula, that inserts into the top of the greater tubercle of the humerus) tenotomy (a surgical cutting of a tendon). This procedure was done to evaluate
the bursa’s effect on the injured supraspinatus tendon, the uninjured infraspinatus tendon, and the underlying humeral head [see Figures 2 and 3]. The bursa protected the intact infraspinatus tendon adjacent to the injured supraspinatus tendon by maintaining its mechanical properties and protected the underlying humeral head by maintaining bone morphometry. The bursa promoted an inflammatory response in injured rat tendon, initiating expression of genes associated with wound healing, including Cox2 and Il6. These results were confirmed in rat bursa organ cultures.[11]
Further evidence using proteomic profiling of bursa tissue samples from nine patients with rotator cuff injury, has documented that the bursa positively responded to injury in the underlying tendon. The theory is that the positive effect is because bursa tissue delivers drugs to the repaired tendon to improve healing.
The Importance of the Research
Figure 3. Coracohumeral ligament shown in red. From Wikimedia Commons.
Close to half of people over 65 have experienced a rotator cuff tear. The pain can make simple daily tasks, such as combing one’s hair, difficult. The result is over 500,000 rotator cuff surgeries are performed each year in the United States alone, “but they frequently fail — ranging from one in five surgeries in young patients to as high as 94% in elderly patients with large tears.”[12] The surgery usually fails due to “poor healing between tendon and bone where the tendon is reattached to the bone. The bursa often becomes inflamed, sometimes concurrently, when underlying tendons are injured, and in this case surgeons often remove the bursa tissue because they wrongly suspected it was a source of shoulder inflammation and pain.[13]
Summary
It has now been documented that the bursa tissue has critical biological roles besides mechanical cushioning, including promoting healing of the shoulder tendons. The “presence of the bursa protected the undamaged tendon by maintaining its mechanical properties and protected the bone by maintaining its morphometry. When the bursa was removed, strength of the undamaged tendon deteriorated and the bone quality deteriorated.”[14] The medical research concluded that
the bursa is not a bystander tissue but rather is an active participant in inflammatory and repair processes after tendon injury. In clinical biopsies and a rodent model of supraspinatus tendon injury, the bursa responded to nearby tendon injury by up-regulating genes associated with inflammation and healing. Bursa removal in the rat altered expression of inflammatory cytokines and had a detrimental effect on the adjacent intact infraspinatus tendon and humeral head. [15]
This finding may turn out to produce a medical revolution in reducing a problem that causes one in five surgeries in young patients to fail. This is yet another case where the evolutionary model has resulted in causing a major detrimental effect on health and wellness. In contrast, and in agreement with this author’s own research on this issue (see Figure 4), use of the creation model and intelligent design has in this case turned out to be a beneficial science model.
References
[1] Smith, H.F., and W. Wright. “Vestigial Organ.” In Vonk, J., and T. Shackelford (editors), Encyclopedia of Animal Cognition and Behavior. Springer Link; https://doi.org/10.1007/978-3-319-47829-6_406-1, 2018.
[2] Prout, T. “Observations on structural reduction in evolution.” The American Naturalist 98(901):239.
[3] Bergman, J. Useless Organs: The Rise and Fall of a Central Claim of Evolution, revised version. Bartlett Publishing, Tulsa, Oklahoma, 2024.
[4] Bland, J., et al. “The painful shoulder.” Seminars in Arthritis and Rheumatism 7(1):21-47; Lippmann, R. K. “Frozen shoulder, periarthritis, bicipital tenosynovitis.” Archives of Surgery 47(3):283-296. doi:10.1001/archsurg.1943.01220150064005, 1943.
[5] Guyot, J. “The Shoulder Girdle and Shoulder Joints.” In: Atlas of Human Limb Joints. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-02322-8_4, p. 102, 1981.
[6] Kennedy, M., et al. ”Clinical anatomy of the subacromial and related shoulder bursae: A review of the literature.” Clinical Anatomy 30(2):213-226, 2016.
[7] Columbia University Irving Medical Center. “Shoulder surgeons should rethink a common practice, study suggests.” 25 April 2024.
[8] Columbia University Irving Medical Center, 2024.
[9] Columbia University Irving Medical Center, 2024.
[10] Columbia University Irving Medical Center, 2024.
[11] Marshall. B. et al., 2014. The subacromial bursa modulates tendon healing after rotator cuff injury in rats. Science Translational Medicine. 16(744). DOI: 10.1126/scitranslmed.add8273. April 24.
[12] Columbia University Irving Medical Center, 2024.
[13] Columbia University Irving Medical Center, 2024.
[14] Columbia University Irving Medical Center, 2024.
[15] Marshall, B.P, et al.
Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,900 publications in 14 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,800 college libraries in 27 countries. So far over 80,000 copies of the 60 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.