Effect of Experimental Pain and Visual Feedback on the Accuracy and Precision of Knee Joint Position Sense.

Objective: To investigate the effects of experimental pain and visual feedback on the accuracy and precision of knee joint position sense following a period of motor training. Methods: Forty healthy young subjects (age: 24.5 ± 3.6 years old) underwent an 8 day motor training. After the training, they were instructed to perform a knee reposition task before and after receiving an injection of either hypertonic (pain group) or isotonic (control group) saline into the infrapatellar fat pad of the left knee. The Visual Analog Scale (VAS) was recorded for both groups. In each condition, participants were instructed to extend their knee to three predetermined target positions (30°, 45°, and 60°) for 10 repetitions, both with visual feedback (VF) and without visual feedback (NVF). The accuracy and precision of the knee reposition task were measured before and after the injection. Accuracy was determined by calculating the mean difference between the target angle and the actual angle achieved, while precision was determined by calculating the standard deviation of all actual angles. Data were analyzed using two-way ANOVAs and independent-samples t-tests to compare the pain and control groups. Results: The VAS were 4.14 ± 2.48 for the pain group and 0.83 ± 0.89 for the control group. There was a significant decrease in knee accuracy after the injection of hypertonic saline compared to movements before the injection during VF (p=0.009). The pain group showed significantly worse knee accuracy compared to the control group in the relative change of performance during VF (p=0.015). Conclusions: This study demonstrates that experimental knee pain impairs the accuracy of joint position sense, even after a period of motor training. This could serve as a helpful cue for individuals with knee pain to pursue timely treatment, thereby reducing the risk of additional injury. Trial Registration: ClinicalTrials.gov identifier: NCT04146311.