Endogenous analgesia, assessed via conditioned pain modulation, is not different in people with hip osteoarthritis compared to controls: a cross-sectional study.

Background: In people with knee osteoarthritis, measures of pain sensitivity have been demonstrated to relate to both pain severity and treatment outcomes, dependent on the type of pain sensitivity being tested.

Objective: Quantify if differences in the pressure pain thresholds (PPT) or conditioned pain modulation (CPM) effect exist between people with hip osteoarthritis and age-matched controls without hip osteoarthritis.

Methods: We performed a cross-sectional study across two geographic locations. PPTs at a local (hip) and remote (elbow) site were collected via a manual algometer. CPM was quantified using PPTs immediately prior to, and during ice water immersion of the hand contralateral to the tested hip. We performed two linear mixed models (hip and elbow) to evaluate between-group (case vs control) differences in PPT over time. Significance was accepted with p < 0.05.

Results: We included 71 participants: 32 with hip osteoarthritis (75 % female sex), and 39 without hip osteoarthritis (82 % female sex). Osteoarthritis participants had significantly lower baseline hip PPTs than control participants (p = 0.038). Hip PPTs significantly increased over time following the conditioning stimulus (p < 0.001). However, we did not detect a significant interaction effect for PPTs between group and time (p = 0.308). There were no significant differences detected in elbow PPT between hip osteoarthritis and control participants (p = 0.114). Elbow PPTs significantly increased over time following the conditioning stimulus (p < 0.001). However, we did not detect a significant interaction for PPTs between group and time (p = 0.606).

Conclusion: This study demonstrates that people with hip osteoarthritis have local, but not widespread, increases in mechanical sensitivity. Further there were no group differences in CPM.