Tendinitis vs. Tendinosis

Tendinitis refers to the inflammation of a tendon. The term has been used for decades, but it’s inaccurate diagnosis resulted in a separate pathology being established – tendinosis.  This latter term was used to describe a patient suffering from the same symptoms as someone with tendinitis, but without the presence of inflammatory cells, or very few of them.

Many physicians have been/still are quick to diagnose pain in the patellar tendon as tendinitis. This is understandable as they are often basing their diagnosis off symptoms the patient is describing to them which may include:

  • pain when I walk up or down stairs
  • pain when I run
  • pain when I jump, especially during sports sports like basketball or volleyball

Tendinitis is almost always an overuse injury, meaning it is a result of repetitive wear and tear.

Tendinosis will have similar symptoms; however, there will be very few to no inflammatory cells present.  Instead, there are a number of internal abnormalities.

A healthy tendon is composed of type I fibers, with few type III fibers mixed in. The type I fibers are laid down very neatly, forming parallel lines. A healthy tendon will look very distinct under a microscope – it will be fairly white and shiny, reflecting polarized light.

Tendinosis, or unhealthy tendons, will have a darker, gray-ish tint to them, not reflecting polarized light under a microscope.  Type III fibers will be far more dominant, resulting in the tendon construction looking rather deformed. There will be a combination of thin and thick fibrils that look like they have been placed haphazardly forming a tendon. Some fibrils may not even be connected to one another, thus seriously compromising the integrity and function of the tendon.

This doesn’t look pretty, but more importantly it has major effects on the ability of the tendon to transmit force and sustain loads. This can result in tendon rupture, muscle imbalances, and frequent pain while participating in many physical activities.

(Any inflammatory cells present in tendinosis will be a result of partial tears or micro tears in the tendon, which is a direct result of the poor tendon structure and functioning.)

Take a look at the difference between a healthy tendon and tendinosis:

You can easily see the difference. Look at how neatly aligned the fibers are in (A), compared to (B). Including this visual should help you understand how poorly unhealthy tendons will function. However, discovering unhealthy tendons requires some intrusive work.  In many cases, a physician will only talk with a patient, or perhaps put them through a movement screen to elicit a response; rarely will they have the opportunity to look at the tendon under a microscope. I can attest to this first hand as I was casually diagnosed with tendinitis a while back. I know now with certainty that it was not solely a case of inflammation.

Neovascularization is also found in tendinosis. This is simply the laying down of new blood vessels. (Neo = new,  vascular = blood vessels). Unfortunately, this process of new blood vessels forming is of little to no help in assisting with the health of tendons. In fact, the vascular structures are often not even functioning blood vessels. They have also been known to form perpendicular to collagen fibers, which is far from optimal positioning.

So as you can see, tendinosis is a pretty bad situation – the tendon is of poor quality, resulting in sub-par functioning. This sub-par functioning can result in tears that exacerbate the problem by adding tendinitis (inflammation) to the mix. There is also an accumulation of near worthless vessels at the site.

OK, but what does all this mean?

The diagnosis has to be accurate because the treatments of tendinitis vs. tendinosis are SO different.

Treatment of tendinitis

Treatment of tendinitis is fairly straight forward – NSAIDs, or Non Steroidal Anti-Inflammatory Drugs such as acetaminophen. Corticosteroids are also used to treat tendinitis.

Tendinitis can be treated within a few days to a number of weeks. However, it can become extremely long term as it may be reoccurring.

Treatment of tendinosis

Treatment should revolve around the encouragement of collagen synthesis and type I collagen growth. This can be done through loading the joint and slowly building up strength in the tendon. This should lead to better alignment of fibres, as well as promote type I synthesis. Proper movement patterns should be emphasized throughout.

Alfredson et al. had a group of 15 people suffering from Achilles tendinosis carry out heavy eccentric loading as a treatment program. They found that all 15 participants were back to their pre-injury activities within a 12 week period.

Another study conducted also found that their participants’ ‘pain scores’ were significantly lower after a 12 week period.

There are other treatment modalities for tendinosis. These include ultrasound and laser surgery; however, the results of these methods are highly controversial.

If mis-diagnosed?

If anti-inflammatories or corticosteroids are prescribed for someone who is in fact suffering from tendinosis, this can accelerate the degenerative process, worsening the situation. This is why an accurate diagnosis is vital.

What can you do?

Obviously you should have trust in doctors and general practitioners, but don’t be afraid to ask a few questions. How are they so sure of the conclusion they came to? You can help them by being as precise as possible – include every minute detail you can recall. There may be that one thing that raises a red flag.

You would be surprised how many mistakes doctors make. In an industry where immense pressure is placed on them to prescribe remedies and diagnose with spot-on accuracy, errors get swept under the rug and there is certainly a denial of any wrong doing.  The system is built around perfection – this may seem like a good model; however, because we are human, this is impossible.  Healthcare and medicine should operate by learning from mistakes and thus minimizing future mistakes. Only then will doctors and physicians be close to achieving this eutopian, perfect working environment.

Here is an excellent TED talk about opening up to the mistakes doctors make.




Alfredson, H., Pietila, T., Jonsson, P., Lorentzon, R. Heavy-Load Eccentric Calf Muscle Training For the Treatment of Chronic Achilles Tendinosis. AJSM. Vol. 26 (3), 1998. pp.360-366



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