Does central sensitization play a role in chronic tendinopathy?
The prevalence of tendinopathies is high both in athletes and in the general population. Despite a wealth of literature, the pain mechanisms of tendinopathies are not well understood.
Currently, some studies have described whether, or to which degree, somatosensory changes within the nervous system may contribute to the pain in tendinopathies.
A patient controlled study was conducted in which the standardised quantitative sensory testing (QST) protocol developed by the German Research Network on Neuropathic Pain was used. This protocol consists of 7 different tests that measures 13 somatosensory parameters and can be seen as the gold standard for measuring somatosensory function.
Twelve athletes with clinically diagnosed patellar tendinopathy (PT), with a mean symptom duration of 30 months, and 20 control athletes were included in the study. In two of the thirteen QST parameters, namely Mechanical Pain Threshold and Vibration Disappearance Threshold, injured athletes were significantly more sensitive for the applied stimuli. None of the athletes had signs of Dynamic Mechanical Allodynia. Reduced mechanical pain thresholds or pinprick allodynia reflects the involvement of central sensitization upon the myelinated (Ad-fibre) nociceptive input. This reduced mechanical pain threshold is a plausible explanation why the pain occurs during or shortly after sports activities which is very characteristic for (patellar) tendinopathies and described in the classification of PT.
In two other studies, with 234 and 74 participants respectively, Pain Pressure Thresholds (PPT) were measured comparing athletes with patellar tendinopathy and healthy athletes. The PPT of asymptomatic athletes differed significantly (p<.001) from athletes with a diagnosis of patellar tendinopathy. The inter-rater (ICC 0.93) and intra-rater (ICC 0.60) reliability of the PPT measurements were adequate to moderate. There was a positive predictive value of 96.5% that athletes with a PPT below 36.8 N had patellar tendinopathy.
In conclusion, it appears that central sensitization might play a role in the onset of pain during and after sports activity in (a subgroup) of patella tendinopathy patients. Although further research is warranted PPT algometry seems to be a feasible, reliable and useful tool in the diagnosis and treatment evaluation of athletes with patellar tendinopathy.
Paul van Wilgen
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