655: No Universal Mechanical Threshold for Pain: Evidence from Knee Acceleration and Impulse in Knee OA

Topic: Experimental (Non-clinical) Human Studies
Subtopic: Non -specific to any diagnosis, Developing methodology/technology, Assessment and Measurement of Pain/Nociception, Pain mechanisms (e.g. descending inhibitory control, placebo, inflammation)

Background and Aims: Quantitative assessment of pain using mechanical parameters remains a major challenge in clinical biomechanics. Our previous study ;IASP2024 using accelerometers demonstrated that reductions in knee acceleration were associated with decreased pain; however, no clear acceleration threshold for pain could be identified.
The present study aimed to further investigate whether a mechanical threshold for pain exists by examining frontal plane knee joint impulse in addition to acceleration-based measures.

Methods: The study population comprised 8 women. All the members were osteoarthritis of the knee.
The participants were tested in two conditions of the "bare foot", "orthosis: lateral wedge insole". The participants walked at their preferred but constant speed 10m. The same experiment was repeated thrice. Walking was measured using VICON. The following parameter was calculated frontal plane impulse. The mean value for each parameter was determined. The frontal plane impulse of two groups compared it in t-test.

Results: Reductions in both knee acceleration and frontal plane impulse were consistently associated with reductions in pain.
However, substantial inter-individual variability was observed in both mechanical parameters and pain responses. No consistent threshold value could be identified that distinguished painful from non-painful conditions across participants.
Instead, pain reduction appeared to occur in a continuous and individualized manner in response to decreasing mechanical load.

Conclusions: Although mechanical stress parameters such as acceleration and frontal plane impulse are associated with pain, a universal threshold for pain does not appear to exist.
These findings suggest that pain is not determined by a fixed mechanical cutoff value, but rather by individualized responses to mechanical stress.
Therefore, mechanical measures are useful for within-subject evaluation of treatment effects, but not for defining universal pain thresholds or for between-subject comparisons.

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Presenting Author: Takahiko Fukumoto
Submitting Author: Takahiko Fukumoto

Senior Author: Takahiko Fukumoto

IASP 2026 Global Year theme of Neuropathic Pain: No

• Hiroshi Maeoka - Kio University