Objectives: Peripherally directed treatments (targeted exercise, surgery) can reduce, but not fully eliminate, pain for up to 40% of patients with Achilles tendinopathy. The objectives of the present study were (1) to identify indicators of altered central processing in participants with Achilles tendinopathy compared to controls, and (2) to determine which indicators of altered central processing would persist after a local anesthetic injection in patients with Achilles tendinopathy.
Design: Mechanistic clinical trial.
Methods: Forty-six adults (23 with chronic Achilles tendinopathy, 23 matched controls) repeated (1) a movement-evoked pain rating, (2) motor performance assessment, (3) pain psychology questionnaires, and (4) quantitative sensory testing. Participants with Achilles tendinopathy received a local anesthetic injection before repeat testing and controls did not. Mixed-effects analyses of variance examined the effects of group, time, and group by time.
Results: The Achilles tendinopathy group had movement-evoked pain, motor dysfunction, and higher pain psychological factors (pain catastrophizing, kinesiophobia) compared to controls (P<.05). The Achilles tendinopathy group did not have indicators of nociplastic pain with quantitative sensory testing (P>.05). In those with Achilles tendinopathy, local anesthetic injection eliminated pain and normalized the observed deficits in heel-raise performance and pain catastrophizing (group-by-time effect, P<.01), but not in kinesiophobia (P = .45). Injection did not affect measures of nociplastic pain (P>.05).
Conclusion: People with Achilles tendinopathy had elevated pain psychological factors and motor dysfunction but no signs of nociplastic pain with quantitative sensory testing. Removal of nociceptive input normalized movement-evoked pain and some indicators of altered central processing (motor dysfunction, pain catastrophizing), but not kinesiophobia. J Orthop Sports Phys Ther 2020;50(6):334-343. Epub 29 Apr 2020. doi:10.2519/jospt.2020.9242.
Keywords: central sensitization; kinesiophobia; kinetics; movement-evoked pain; nociceptive.