The Chemistry of Tendonitis


One of the most widely used terms to define joint pain within the body is the term tendonitis. Tendonitis is the inflammation and/or irritation of a specific tendon or a group of tendons. Usually, ankle tendonitis occurs in the peroneus longus or brevis tendon and is classified in either the chronic or acute categories. Acute injuries are usually seen as inversion ankle injuries or powerful contraction of the peroneal muscles with a forcefully dorsiflexed foot. The general perception of tendonitis is often presumed as a catch-all term for pain in a specific region of the body, however, most medical professionals will reference a specific tendon when issuing a diagnosis.

Throughout my life, I have been very active in sports, but, often after periods of high athletic intensity, I would experience pain in the dorsal aspect of my ankle. I often attributed this to tendonitis of the ankle and wore numerous braces to stabilize my foot/ankle, iced and rested often, went through physical therapy, and even had acupuncture done to the inflamed area. During periods of rest, my ankle would recover to a point of being pain-free, but would return to the irritated and painful state during physical activity.

After seeing many physical medicine rehab doctors, my ‘tendonitis’ was diagnosed to a cuboid inflammation on my peroneal brevis tendon, which was caused due to the irritation of the tendon attachment to the bone.

Composition of ...

    • Tendon(s)
      • Collagen fibers (mainly types I and III)
      • Fibroblasts (predominant cell types)
      • Proteoglycans (mainly decorin and lumican)
      • Tenoblasts and tenocytes (90-95% of cellular elements)
      • Chondrocytes (remaining 5-10% of cellular elements)
    • Molecules/Proteins
      • Proteoglycans
      • Glycosaminoglycans
      • Glycoproteins
      • Tenascin-C

Main Chemicals, Compounds, Components


Tendons are predominantly composed of collagen fibers embedded in proteoglycan matrix that attracts water and elastin molecules with a relatively small number of fibroblasts, the main blood cell type in tendons. Fibroblasts are spindle shaped and arranged in fascicles with surrounding loose areolar tissue called peritenon. Within the extracellular matrix network, tenoblasts and tenocytes constitute about 90-95% of the cellular elements of tendons. The remaining 5-10% of the cellular elements of tendons consist of chondrocytes at the bone attachment and insertion sites, synovial cells of the tendon sheath, and vascular cells, including capillary endothelial cells and smooth muscle cells of arterioles.

There are two main types of collagen in a tendon; collagen type I and type III. Type I collagen is the major component of tendons, also accounting for about 90-95% of the dry tendon’s weight. Collagen type III accounts for about 5% of the dry tendon’s weight. However, collagen type V,VI, XII, and II are present but at extremely smaller quantities. Proteoglycans, also knowns as PGs, account for the remaining 1-5% of the dry weight of tendons. The most accounted types of proteoglycans in the tendon are decorin and lumican. Because decorin molecules form cross-links between collagen fibers, they may increase the stiffness of the fibrils.

The epitenon, a fine, loose connective-tissue sheath containing the vascular, lymphatic, and nerve supply to the tendon, covers the whole tendon and extends deep within it between the tertiary bundles as the endotenon. The endotenon is a thin reticular network of connective tissue investing each tendon fiber. Superficially, the epitenon is surrounded by paratenon, a loose areolar connective tissue consisting of type-I and type-III collagen fibrils, some elastic fibrils, and an inner lining of synovial cells.


The ground substance of the extracellular matrix network surrounding the collagen and the tenocytes is composed of Proteoglycans, Glycosaminoglycans, Glycoproteins, and Tenascin-C.

Proteoglycans are glycoproteins which have a very high polysaccharide content. They are strongly hydrophilic, enabling rapid diffusion of water-soluble molecules and the migration of cells. Glycosaminoglycans are long, unbranched polysaccharides with a continuing disaccharide unit made of one of two modified sugars: N-acetylgalactosamine (GalNAc) or N-acetylglucosamine (GlcNAc), or a uronic acid such as glucuronate (GlcA), also known as iduronic. Common forms of glycoproteins are fibronectin and thrombospondin. These glycoproteins participate in repair and regeneration processes in tenons. Tenascin-C is abundant in the tendon body and is often found at the osteotendinous and myotendinous junctions. Tenascin-C may also play a role in collagen fiber alignment and orientation.

Chemistry's Role

There is not a lot of actual chemistry involved in tendonitis of the ankle. However, there is some chemistry in the inflammation and medication involved in the treatment/dealing with this particular pain. For example, inflammation of the tendon may involve chemical irritants such as histamine, bradykinin, serotonin, prostaglandins, and cyclooxygenase. This inflammation may also occur due to the toxins and alcohol in the blood reacting with one another as well.

Medication for tendonitis can sooth the pain and possibly aid in the lessening of inflammation of the infected area. Medication such as Ibuprofen, Advil, and Aleve have a certain compound in them that blocks the creation of the cyclooxygenase (COX) chemical. The stoppage of this chemical lessens the pain in an injured area.

Background Research

Ankle tendonitis can have many causes such as overuse, a dormant injury, an abnormal foot structure, and/or other medical conditions that are already in effect. Symptoms include pain, swelling, and often stiffness of the ankle and foot region. There are many different types of tendonitis that can occur in the ankle. One of the most common areas is located in the achilles and causes heel and calf pain. The posterior irritation affects the inner side of the foot while peroneal irritation affects the back and outer side of the ankle, foot, and/or leg. Extensor pain involves the top of the foot and anterior tendonitis affects the front of the foot closer to the toes.

As stated previously, many patients with tendonitis have inflammation as well as pain. The response of inflammation consists in changes in blood flow, an increase in the permeability of blood vessels (histamine), and the transmission of white blood cells, proteins, and different fluids to the affected area. The chemicals involved in inflammation originate from blood, plasma, white blood cells (basophils, neutrophils, monocytes, and macrophages) damaged tissue cells, and platelets.

Because tendonitis is the inflammation of a tendon and can prohibit you from many activities if not taken care of, treatment is a crucial part of healing this irritant. Often doctors will recommend that their patient undergo the RICE procedure (Rest, Ice, Compression, and Elevation) as well as getting over-the-counter medication such as ibuprofen or aspirin to lessen any pain or swelling. In many severe or chronic cases, immobilization such as a brace or a cast may be required for faster healing. Surgeries are also available to alleviate some of the buildup within the area of pain. If the present inflammation is too great and surgery does not help or heal the problem, surgeons will often extract the calcium buildup that comes with chronic tendonitis. Acupuncture and herbal remedies help to alleviate pain or reduce swelling as well.

Tendonitis can be reaquired throughout the patient’s life. To avoid having to deal with tendonitis again, doctors recommend warming up thoroughly before activity and conditioning your body for the task before hand. Having shoes that give enough support for an activity you wish to pursue and avoid running or stepping on uneven surfaces if at all possible will also help to limit the tendonitis of the ankle or foot. But, as with all bodily functions and pains, the patient must listen to their bodies and allow themselves to heal before undergoing major physical activity.


What tendons are affected and which categories these injuries would fall into.

What acute tendon injuries are seen as and often mistaken for.

What ankle tendonitis results in.

The causes, symptoms, and types of tendonitis.

How inflammation occurs in an area.

The chemical properties of inflammation.

Treatment such as calcium removal, acupuncture, and herbal remedies to reduce swelling.

The anatomy of the ankle.

"Chapter 2." The Physiology of Sports Injuries and Repair Processes. Web. 14 Dec. 2015.

The Histo Anatomical features of tendons (pdf).

Sharma, Pankaj. "Tendon Injury and Tendinopathy: Healing and Repair." The Journal of Bone and Joint Surgery (American) J Bone Joint Surg Am (2005): 187. Print.

The structure of tendons (article).

Molecules and proteins (Proteoglycans, Glycoproteins, Tenascin-C) involved in ankle tendonitis (article).

Proteoglycans: what they are and what they do in terms of tendonitis.

Glycosaminoglycans: what they are and what they do in terms of tendonitis.

How to prevent and treat foot and ankle tendonitis.

Background music for the video.

About the Author

Heather Murray is a junior at Billings Senior High School. Heather is apart of many activities such as STEM society, Senior Advocates, Varsity Singers/Choir, and extra curricular honors choirs. She was also chosen to be a a part of the All-State and All-Star choirs of 2014, as a sophomore, and 2015, as a junior. As well as being involved in many choirs, Heather was also part of the basketball team at Senior as a freshman and sophomore. Outside of school, Ms. Murray enjoys traveling, going to the beach to visit family, and spending time with friends and family.