Effect of experimentally induced knee pain on standing balance in healthy older individuals.

OBJECTIVE Standing balance is impaired in older individuals with knee pain. The extent to which this impairment is due to the effects of pain itself or other pathophysiological aspects related to the underlying musculoskeletal condition causing the pain is unclear. To isolate the influence of pain, this study evaluated the effect of experimentally induced knee pain on standing balance in healthy older individuals. METHODS We used a repeated-measures, within-subject design involving 12 healthy individuals aged 50-60 yr and with no history of knee pathology. Balance was tested during two randomly allocated experimental conditions: (i) control and (ii) knee pain induced by injection of hypertonic saline into the infrapatellar fat pad. Balance was measured using a computerized force platform under static and dynamic conditions as well as via the functional step test. RESULTS Standing balance was not significantly altered by experimentally induced acute knee pain, nor was there any relationship between the severity of reported pain and balance scores. CONCLUSIONS Impairments in balance associated with knee conditions such as osteoarthritis may be due to factors other than the sensation of pain. Thus, strategies designed to reduce pain in treatment of knee pathology may not necessarily lead to improvements in balance. Further research is required to determine the exact causes of balance impairment in individuals with knee joint pain and pathology.