Healthy tendons are made up of densely packed, parallel collagen (connective tissue) fibres. This specific structure of tendons is what makes them so strong and resilient. The blood vessels that supply tendons also run parallel to these fibres, but the inner part of the tendon has a relatively poor blood supply.
With overuse or overloading there will be thickening of the tendon to reduce stress on the tendon. There isn’t any inflammation during this phase and, if the load is reduced in time, there isn’t any permanent damage to the tendon. However, the thickening can cause some loss of flexibility. This process is called a reactive tendinopathy. A normal tendon responds to load and tension by stiffening, so the thickening is your body’s way of compensating for a lack of stiffness, trying to heal the tendon. Therefore your tendon works like a worn out spring that struggles recoil & expand.
This is usually caused by a sudden increase in activity, for example someone who doesn’t normally run doing a trail run. Falling directly on your knee will also case
If a reactive tendinopathy is not managed properly – by decreasing the load on the tendon – the body will carry on this “healing” process. Unfortunately, this phase is different, because there is an increase in other cells in the tendon (not just collagen). These cells cause separation and disorganisation of the normal collagen in the tendon and small blood vessels develop in the inner part of the tendon, disrupting the tendon’s fibers from absorbing load. This is the tendon disrepair phase.
We normally see this condition if people carry on training through the pain for weeks of months. The tendon doesn’t have time to adapt in between the activities that cause the quadriceps tendinitis, like downhill running every day for weeks or repeated falls on your knee.
This phase is normally seen in older patients or athletes who kept on overloading the tendon for months or years. If you reach this phase, your condition cannot be reversed, because there are areas of “dead” tendon that cannot heal. These areas have lots of small blood vessels and very little collagen.
It’s not all bad news though, because there will still be areas of the tendon that can heal and this is what we as physiotherapists will focus on during treatment.