Contralateral mechanical hyperalgesia and altered pain modulation in men who have unilateral insertional Achilles tendinopathy: A cross-sectional study

Objective: The primary aim was to assess whether men who have insertional Achilles tendinopathy (IAT) have altered endogenous modulation of painful stimuli, and secondarily if they exhibit unaffected-side pressure hyperalgesia. Methods: Using a cross-sectional design, we recruited men with unilateral IAT and asymptomatic men as controls matched for age, body mass index (BMI) and activity history (participation in running, lower limb loading sport or sedentary). We collected pressure pain threshold (PPT) at the asymptomatic side Achilles tendon insertion for cases, and dominant side Achilles tendon insertion for controls. We compared PPT between groups before and after immersion of the hand in painful cold water. Results: Twenty men with unilateral IAT (45.4 years [SD 10.02], BMI 29.09 [SD 4.61], 60% sedentary) and 34 men without symptoms (43.2 years [SD 8.78], BMI 27.59 [SD 3.18], 50% sedentary) participated. An interaction effect was found for group x time (F (1,50) = 7.67, p = 0.008), with PPT increase after cold water immersion being 1.20 (95%CI 0.25 to 2.15) Kg greater in the control group (1.44 Kg [SD 1.79]) compared to IAT unaffected side (0.24 Kg [SD 1.47]). Before cold water immersion, PPT was 4.77 (CI 3.22 to 6.31; p < 0.001) Kg greater in the control group. Discussion: This study provides evidence men with IAT have altered endogenous modulation of a painful stimulus, and display pressure hyperalgesia at their unaffected side compared to men without symptoms. These findings infer alterations to pain processing in men with IAT, suggesting nociplastic mechanism(s) may contribute to pain.

Automated summary

This study provides evidence that men with insertional Achilles tendinopathy have altered endogenous modulation of a painful stimulus, and exhibit pressure hyperalgesia at their unaffected side compared to men without symptoms. These findings suggest alterations to pain processing in men with IAT, potentially involving nociplastic mechanisms.