Patients who are obese and experience knee pain were found to have improved pressure pain threshold at the patella and the wrist after weight loss associated with bariatric surgery vs medical management in a study published in Arthritis Care & Research. This finding suggests that bariatric surgery may result in improved central pain sensitization.

Researchers recruited patients with obesity and knee pain planning to undergo bariatric surgery (n=45; mean age, 43.8 years) or medical management (n=22; 48.1 years) for weight loss. Knee pain and pressure pain threshold were assessed prior to surgery and 12 months postsurgery with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and a hand-held algometer, respectively. Pressure pain threshold was measured for the index patella and the right wrist.

Patients in the surgery group had a higher mean weight loss (32.7 kg) compared with patients in the medical management group (4.6 kg). The mean WOMAC score was reduced from baseline in the surgery group (-4.9; P <.0001) but not in the medical management group (-1.5; P =.13). In a similar manner, the number of joints with frequent pain were significantly reduced from baseline in the surgery group (-2.3; P. =002) but not in the medical management group (0.9; P =.41).

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Pressure pain thresholds in the index patella and in the wrist were improved from baseline in the surgery group (P =.0007 and P =.005, respectively). According to the researchers, the change in pressure pain threshold in the patella could reflect changes in peripheral or central sensitization, and the observed change in pressure pain threshold in the wrist is likely to reflect improved central sensitization. The medical management group did not experience changes in pressure pain threshold from baseline in the wrist or knee.

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The investigators concluded that, “improvements in joint pain in those who experience significant weight loss are likely to be due, in part, to improvement in sensitization, including effects on pain beyond reduced loading across painful knee joints.” They suggested that future research might, “consider the role of inflammatory markers in the circulation, adipocytokines, or metabolic parameters (eg, type 2 diabetes) that improve after bariatric surgery.”

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Stefanik JJ, Felson DT, Apovian CM, et al. Changes in pain sensitization after bariatric surgery [published online January 5, 2018]. Arthritis Care Res (Hoboken). doi: 10.1002/acr.23513