Impacts of Experimental Knee Pain on Gait Biomechanics and Pain Sensitivity: A Randomised Crossover Trial of Young and Pain‐Free Volunteers

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ABSTRACT Background Knee osteoarthritis is hallmarked by pain and structural changes, impacting biomechanical function. However, the interplay between pain and biomechanics is poorly understood. Experimental knee pain may act as a surrogate model of clinical pain to study potential changes in pain mechanisms and biomechanics. Methods This randomised, controlled crossover study induced knee pain with hypertonic saline (7%) injected into the infrapatellar fat pad, controlled by isotonic saline (0.9%) injections. Gait biomechanics (speed, braking impulse, propulsion impulse) were measured using motion capture. Cuff‐pressure algometry estimated pressure pain and tolerance thresholds (PPT and PTT), temporal summation of pain and conditioned pain modulation. Sleep, depression, anxiety, pain catastrophizing and pain were assessed by questionnaires. Results Thirty‐four young, healthy participants had a mean peak pain of 58 (0–100) after the hypertonic saline injection. Changes in PPT ( F (2,62) = 8.0, p < 0.001) and propulsion impulse ( F (1.8,50.0) = 1.79, p = 0.039) were observed after pain induction. Multiple linear regression revealed that a combination of baseline PPT, depression scores, speed and propulsion impulse explained 38.7% of the variability in peak knee pain ( F (4,29) = 4.6, p < 0.01), while a combination of PTT, speed, braking and propulsion impulse measured during experimental pain explained 57.4% ( F (4,29) = 9.8, p < 0.001) of the variability. Conclusion Changes in PPTs and propulsion impulse were observed after the knee pain induction. Peak knee pain variability can be partly explained using a combination of biomechanics, pain sensitivity and cognitive factors. This forms the basis for a targeted clinical evaluation of patients. Significance Statement Knee osteoarthritis has been increasingly recognised as a multifactorial condition influenced by, for example, cognitive factors and pain sensitivity. This study demonstrated an experimental pain model that mimicked clinical pain experienced by people with moderate‐to‐severe OA pain. Additionally, this study provides novel insights into the interplay between pain sensitivity, biomechanics and cognitive factors and experimental knee pain.

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