The Journal of Arthroplasty , Volume 33 , Issue 7 , S71 - S75.e2

How Much Pain Is Significant? Defining the Minimal Clinically Important Difference for the Visual Analog Scale for Pain After Total Joint Arthroplasty

Danoff, Jonathan R. et al.
Hip Knee

Background

The ability to detect changes in patient-perceived pain after total joint arthroplasty (TJA) is critical to manage postoperative pain. The minimal clinically important difference (MCID) for visual analog scale for pain (VAS-P) has not been investigated in this population. This study investigated the MCID for VAS-P in the TJA population.

Methods

Postoperative pain scores were collected on 139 total hip arthroplasty (THA) and 165 total knee arthroplasty (TKA) patients. VAS-P was measured and Likert scores for changes in pain recorded together throughout the hospitalization per patient. Using a linear mixed model, the mean difference between preceding and current VAS-P was calculated and correlated with Likert score, when the patient reported at least slight improvement or worsening in pain, defining the MCID. Minimal detectable change was calculated using the VAS-P standard error of the means for patients reporting “no change.”

Results

For THA, the overall mean and average highest VAS-P were 35.0 mm and 50.4 mm, respectively. For TKA, the overall mean and average highest VAS-P were 42.6 mm and 61.1 mm, respectively. The minimal detectable change in VAS-P was 14.9 mm for THA and 16.1 mm for TKA. The MCID for THA and TKA pain improvement was −18.6 mm and −22.6 mm, respectively, and for worsening was 23.6 mm and 29.1 mm, respectively.

Conclusion

In the postoperative TJA population, VAS-P MCID changes depend on the type of surgical intervention, and whether pain is improving or worsening. Statistically significant VAS-P, improving −18.6 mm and −22.6 mm for THA and TKA patients, respectively, sets a reasonable threshold to identify clinically meaningful pain intervention with high specificity.


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