Increased pain sensitivity but normal function of exercise induced analgesia in hip and knee osteoarthritis – treatment effects of neuromuscular exercise and total joint replacement

Summary Objective To assess exercise induced analgesia (EIA) and pain sensitivity in hip and knee osteoarthritis (OA) and to study the effects of neuromuscular exercise and surgery on these parameters. Design The dataset consisted of knee ( n = 66) and hip ( n = 47) OA patients assigned for total joint replacement at Lund University Hospital undergoing pre-operative neuromuscular exercise and 43 matched controls. Sensitivity to pressure pain was assessed by pressure algometry at 10 sites. Subjects were then instructed to perform a standardized static knee extension. Pressure pain thresholds (PPTs) were assessed at the contracting quadriceps muscle (Q) and at the resting deltoid muscle (D) before and during contraction. The relative increase in PPTs during contraction was taken as a measure of localized (Q) or generalized (D) EIA. Patients were assessed at baseline, following on average 12 weeks of neuromuscular exercise and 3 months following surgery. Results We found a normal function of EIA in OA patients at baseline. Previous studies have reported beneficial effects of physical exercise on pain modulation in healthy subjects. However, no treatment effects on EIA were seen in OA patients despite the increase in muscle strength following neuromuscular exercise and reduced pain following surgery. Compared to controls, OA patients had increased pain sensitivity and no beneficial effects on pain sensitivity were seen following treatment. Conclusions To our knowledge, this is the first study of EIA in OA patients. Despite increased pain sensitivity, OA patients had a normal function of EIA.