Doctor of Philosophy
Health Related Sciences
Daniel L. Riddle
Benjamin J. Darter
SMALLEST WORTHWHILE EFFECT VALUES FOR PAIN AND FUNCTION AFTER A TOTAL KNEE REPLACEMENT
Nancy Henderson, PT
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Virginia Commonwealth University.
Virginia Commonwealth University, 2020
Dr. Dan Riddle, PT, PhD, Physical Therapy
Meaningful change is an important concept in healthcare as it allows providers to better understand the efficacy of an intervention. Three commonly used methods to assess meaningful change include the distribution-based, anchor-based, and benefit-harm trade-off methods. The benefit-harm trade-off method improves upon the limitations of the distribution-based and anchor-based methods. Unlike the other two methods, the benefit-harm trade-off method allows patients to determine clinically meaningful change by assessing the benefits and risks of an intervention compared to no intervention. The smallest worthwhile effect is a response measure which is derived using the benefit-harm trade-off method. The primary aim of the current study was to determine smallest worthwhile effect values for pain and function following a Total Knee Replacement.
This study enrolled 121 participants. A standardized script was used to determine smallest worthwhile effect values for the KOOS Pain and KOOS function, daily living subscales. A feasibility study was initially conducted to assess feasibility of subject recruitment, locations for data collection, and to assess wording and interpretability of the standardized script. Baseline and psychosocial variables were assessed for their influence on smallest worthwhile effect values. A 6-month follow-up, via telephone, was conducted to determine if participants achieved their smallest worthwhile effect values and to determine patient satisfaction and complication rates.
The results of this study demonstrated that 90% of participants needed at least a 57 point improvement in their KOOS Pain subscale scores, over their baseline pain, to feel that the surgery was worthwhile as compared to not having surgery. Similarly, 90% of participants needed at least a 51 point change on their KOOS Function, daily living subscale scores to view the surgery was worthwhile when compared to not having a knee replacement. Baseline scores on the KOOS Pain and Function, daily living subscales were the only significant predictors of smallest worthwhile effect estimates. Eighty-three of the 121 participants completed the 6-month follow-up. Of the six month follow-up participants, 91% were satisfied with their current state. There was a significant association between meeting or exceeding the smallest worthwhile effect estimates for the KOOS Pain and Function, daily living subscales and patient satisfaction.
The smallest worthwhile effect estimates generated in the current study are higher than response measures calculated using the distribution- and anchor-based methods. The higher estimates in the current study may ultimately mean that individuals require more benefit after surgery, as previously thought, when costs and risks are factored into determining meaningful change following a knee replacement. Those individuals with higher baseline pain and worse preoperative function required a greater improvement after surgery to feel that the surgery was worth the associated costs and risks. Surgeons and patients should factor baseline pain and function into their decision whether or not to undergo a knee replacement. The association between smallest worthwhile effect estimates and patient satisfaction further strengthens the use of the smallest worthwhile effect estimate as an accurate measure with which to estimate meaningful change.
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