The Sphygmomanometer Pain Test: A Simple Method for Identifying Patients at Risk of Excessive Pain after Total knee Arthroplasty

Background: Despite the overall success of total knee arthroplasty (TKA), a relatively large proportion of patients remain dissatisfied with the outcome. We hypothesized that patients with a lower threshold for pain were more likely to have worse outcomes after TKA. Methods: Forty-eight consecutive patients with primary knee osteoarthritis graded a standardized painful stimulus caused by inflating a sphygmomanometer placed on the forearm, on a visual analog scale (VAS) scale before their TKA. We compared the VAS scores to patients' Knee Society scores and Knee Society function scores 2 years after TKA. Results: Patients with a severe VAS score (>74 mm) had significantly worse Knee Society scores compared to patients with mild (0-44 mm) and moderate (45-74 mm) VAS scores (55 ± 20.5 vs 81.5 ± 11.1 and 84.8 ± 13, respectively, P =.04) and worse Knee Society Function scores (34 ± 20.7 vs 75.2 ± 17.3 and 77 ± 17.4, respectively, P =.027) at 2 years after TKA. Conclusions: Patients with a lower threshold for pain, as determined by a standardized painful stimulus, are more likely to have lower Knee Society pain and function scores after TKA.