Minimal clinically important difference for HSS of patients with primary osteoarthritis after total knee arthroplasty

  Objective  To identify the minimal clinically important difference (MCID) for hospital for special surgery knee score (HSS) after total knee arthroplasty (TKA).

  Methods  A retrospective analysis was performed in patients diagnosed with primary knee osteoarthritis and treated with unilateral TKA from January 2017 to June 2018 in the department of orthopaedic surgery of the First Medical Center of Chinese PLA General Hospital. Pre-operative and 1 year postoperative HSS scores and 1 year postoperative satisfaction for 413 patients undergoing a primary TKA for osteoarthritis were collected. Simple linear regression was used to calculate the MCID for improvement HSS score according to the level of patient satisfaction after 1 year.

  Results  The mean age of the 413 subjects was 66±7.8 years. There were 320 (77.5%) female and 93 (22.5%) male subjects. In average, the HSS improved by 34.33 (95% CI : 33.11-35.54) points. The level of satisfaction was excellent in 59 cases, very good in 131 cases, good in 177 cases, fair in 34 cases, and poor/terrible in 12 cases. The changes in HSS in excellent group was 44.96 (95% CI:42.51-47.41), very good group 38.44(95% CI:36.74-40.14), good group 32.26(95% CI: 30.71-33.81), fair group 20.45(95% CI: 17.35-23.55), poor/terrible group 8.08(95% CI: 2.83-13.34). The MCID identified for HSS was 9.18 (95% CI: 6.37-11.98). changes in HSS between each group varied significantly; The HSS improved by 34.33 (95% CI: 33.11-35.54) points. The MCID identified for HSS was 9.18 (95%CI: 6.37-11.98).

  Conclusion  This study has determined that the MCID for HSS in patients with knee osteoarthritis is 9.18 points at 1 year after total knee arthroplasty. It is recommended 9.18 can be set as the cut-off score to evaluate clinical significance.