Shunxing Wang,1,2,* Shuxin Yao,1,* Peng Xiao,3,* Lei Shang,4 Chao Xu,1,4,* Jianbing Ma1,* 

1Department of Knee Joint Surgery, Honghui Hospital, Xi’an Jiaotong University, Xi’an, People’s Republic of China; 2Xi’an Medical University, Xi ‘An, People’s Republic of China; 3Department of Orthopedics (International Ward), Hospital of Chengdu University of Traditional Chinese Medicine, Chengdu, People’s Republic of China; 4Department of Health Statistics, Faculty of Preventive Medicine, the Air Force Military Medical University, Xi’an, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Jianbing Ma, Department of Knee Joint Surgery, Honghui Hospital, Xi’an Jiaotong University, No. 555 E.Youyi Road, Xi’an, 710061, People’s Republic of China, Email drmajianbing@163.com

Purpose: Research on the Minimum Clinically Important Difference (MCID) of the Brief Pain Inventory (BPI) following Total Knee Arthroplasty (TKA) is limited. This study addresses this gap by determining the MCID of the BPI for patients undergoing primary TKA.
Patients and Methods: This study was designed to quantitatively determine the MCID of the BPI for patients undergoing primary TKA. A prospective cohort of 288 patients was evaluated, with the BPI administered both preoperatively and at a one-year follow-up. The MCID was calculated using two primary approaches: the anchor-based method, considered the gold standard, and the distribution-based method. Additionally, this study explored various calculation approaches within the distribution-based framework, benchmarking them against the anchor-based method. The distribution-based methods included calculations based on Standard Deviation (SD), Effect Size (ES), Standardized Response Mean (SRM), and Standard Error of Measurement (SEM). All statistical calculations were performed using established formulas.
Results: The anchor-based method determined the MCID for BPI pain severity to be 3.9 points, the pain interference dimension to be 5.8 points, and the total score to be 9.7 points. Comparisons with the gold standard highlighted the 0.65ES, 1.96SEM, and 0.5SRM methods as the most suitable approaches for distribution-based MCID estimation.
Conclusion: The MCID for BPI in TKA patients was established using both anchor-based and distribution-based methods. When anchor-based determination is impractical, the distribution-based methods— 0.65ES, 1.96SEM, and 0.5SRM—are recommended for MCID calculation.
Plain Language Summary: Understanding whether a treatment makes a meaningful difference to patients is crucial. This study focuses on determining the Minimum Clinically Important Difference (MCID) of the Brief Pain Inventory (BPI) for individuals undergoing Total Knee Arthroplasty (TKA). The MCID helps identify the smallest improvement in pain that patients perceive as beneficial and significant enough to influence their care. By analyzing BPI scores before and one year after surgery, the study used two methods: anchor-based (considered the gold standard) and distribution-based approaches. Various calculation techniques within the distribution-based method were compared to the anchor-based method. The results showed that when the anchor-based method is not feasible, specific distribution-based methods, such as 0.65ES, 1.96SEM, and 0.5SRM, can reliably estimate the MCID. These findings provide clinicians with clear benchmarks for interpreting pain outcomes, ensuring a patient-centered approach to post-TKA care.

Keywords: brief pain inventory, total knee arthroplasty, minimal clinically important difference, patient-related outcome, quality of life