Please Note! The next section is going to get a bit technical. If you have previously had or currently do have a tendon injury (or you are a health professional) this section is well worth reading. If you would like to skip the details and just see how to get things fixed… jump to the bottom!
Tendinopathy is a broad term that encompasses painful conditions occurring in and around tendons in response to overuse. The previous term tendinitis worked on a old paradigm that inflammation was involved in tendon injury however more recent studies show painful tendons are devoid of inflammatory cells. What that means is that dysfunction here doesn't follow normal inflammatory/histological processes that we may find with muscle or bony injury and has no clear end-point. Instead, the pathology involves complex and ongoing non-inflammatory alterations in the tendon matrix and cells. It is essential to understand this, as it underpins how we choose to treat and assess the injury.
Loading changes are the primary stimulus that appears to drive the tendon response towards pathology. Repetitive energy storage and release and excessive tendon compression appear to induce pathology.
Most tendinopathies in the body usually occur at what we call the enthesis - this is the point at which the tendon inserts onto the bone. The only exception to this is a mid-portion achilles tendinopathy. At the enthesis, there are two main factors which influence the amount of stress that happens at the tendon:
1) tensile load from the loading through collagen fibres of the tendon when there is muscle use and 2) compression load around a bony insertion point (as most insertions work around a bony pulley - e.g. heel bone of the achilles).
In mid-portion achilles tendinopathy - tensile load is the biggest factor leading to tendon pathology - mainly the stretch-shorten storage and release of energy (e.g. jumping).
Loading a tendon causes matrix and cell deformation, and depending on the type and amount of load, the cell responds by producing matrix proteins (mainly collagen). Exercise increases collagen production that may contribute to increased tensile strength of a tendon however, there appears to be a fine line between load that stimulates a positive tendon response and load that triggers a negative response. Due to this, tendons are SLOW TO ADAPT TO CHANGE!! This is critical to understand why tendon rehabilitation takes so long, and also why a sudden change in training can cause pain in the first place. Tendons take up to 3 days after a bout of loading to respond to that load. If we load it too quickly before that point, then we can easily send the tendon over the edge.
Researcher Physiotherapist Jill Cook and colleague Craig Purdam have done extensive research into tendon pathology and rehabilitation. Just google their names with ‘tendinopathy’ and you’ll find pages and pages of research on the topic by these two. After overload in a tendon they propose a three stage tendon pathology continuum:
1) reactive phase - this is an acutely overloaded tendon. At this early stage, the tendon can revert to normal if the overload is discontinued or there is sufficient time between loads for the tendon to recover.
2) disrepair phase - this is essential failed healing and results from ongoing load to a reactive tendon, causing structural disorganization of the internal tendon substances resulting in some separation of the collagen and reducing its loading capacity.
3) degenerative phase - progression to extreme changes to a disordered internal structure, cell death and little collagen. These patients will usually have times when are pain free and will continuously recur over and over again.
Figure 1 from Cook & Purdam (2009)