Patients with chronic pain often present with hyperalgesia, possibly due to hyperexcitability of nociceptive pathways. The aim of the present study was to investigate alterations in flexor withdrawal reflex (FWR) excitability in individuals with knee osteoarthritis (OA) and the potential effect of specific physical inputs or therapeutic interventions (ie, joint compression and mobilization) on these behaviors. Ten subjects with and 10 without knee OA (age 45-75) were recruited. The FWR was examined utilizing suprathreshold, noxious electrocutaneous stimuli applied at the medial foot. Surface electromyographic (EMG) was recorded from the tibialis anterior (TA) and biceps femoris (BF), and peak joint torques recorded at the hip, knee, and ankle. FWR threshold was ascertained and responses at 2x threshold recorded after the following conditions: a maximal, volitional, joint-compression task, a sham hands-on intervention, and a Grade III oscillatory joint-mobilization intervention. A decreased threshold-to-flexor withdrawal response was found in the OA vs control group (P < .01). EMG and joint-torque FWR responses were further augmented in the OA group following the maximal joint-compression task (P < .05), yet remained unchanged or diminished in controls. Joint mobilization, but not sham intervention, reduced reflex responses significantly, although primarily by decreasing BF activity and knee torques (P < .05).
Perspective: Application of specific physical inputs to individuals with knee OA similar to those encountered during activity of daily living or during therapeutic interventions appear to modulate involuntary, nociceptive reflex responses. Routine weight-bearing activities such as walking may potentially enhance heightened FWR responses, while joint mobilization, a commonly used clinical intervention, may diminish reflex excitability.
Copyright 2010 American Pain Society. Published by Elsevier Inc. All rights reserved.