Fu’s theory of failed healing (that’s a mouthful!), stems from the belief that there is release of pro-inflammatory mediators causing relevant metallpotonise release and hence collagoynic injuries. A tendon that was previously damaged therefore may not have healed adequately prior to an external load being added/increased . At this point Fu believes mechanical weakness and pain are not significant and therefore the tendon still has the ability to heal spontaneously. This is different from the reactive stage described by Cook and Purdum, where the cells are activated but no damage is described.
The failed healing stage occurs when the cells are not able to repair the collageniylic injuries and the exact cause of this is unknown. It is widely appreciated that tendon healing requires many sequential process’s in order to repair damaged tissue.
- neural ingrowth,
- recruitment of healing cells,
- proliferation and
Somewhere along this process disturbances occur. Either the tendon has not received significant rest in order for these processes to happen, or the initial inflammatory process is disturbed by the prescription of NSAIDS causing an increase in pro-inflammatory cytokaines and not the ordinary inflammatory infiltration into the damaged tissue. Fu also surmises that depending on the location of the pathology, there could be a peritendious reaction which may lead to a restrictive fibrosis due to increased innervations and vascular in-growth may also occur from the paratendon.
Symptomatic tendons are diagnosed by activity related pain and medical imaging. Rupture will occur due to mechanical weakness in the tendon. The pain mechanisms in this phase are now non-phlogstic such as agitation to periteninous nerves by nocioceptive substances and swelling. Due to the failed healing response previously mentioned, tendons will not be homogenious in their presentation, depending on which stage of the healing has been distrupted. Fu suggests that new treatments could be based on this failed healing model,” to override on the failed healing tissues and restart the healing process”.