MCID achievement in staged bilateral total knee arthroplasty: Are both joints created equal?

A notable portion of unilateral total knee arthroplasty (TKA) patients undergo arthroplasty of the contralateral knee. The aims of this study were to describe the Minimal Clinically Important Difference for Improvement (MCID-I) and Worsening (MCID-W) in staged bilateral TKAs (BTKAs) and identify factors associated with these outcomes.

Patients with staged BTKA were retrospectively reviewed. Demographics, surgery details, and Patient-Reported Outcome Measurement Information System Physical Function Short Form 10a (PROMIS PF10a) were collected. MCID-I and MCID-W were defined for PROMIS PF10a. Patients were stratified into nine groups based on the MCID achievement of the first and second TKA: (A) MCID-I, MCID- I, (B) MCID-I, Neutral, (C) MCID-I, MCID-W, (D) Neutral, MCID-I, (E) Neutral, Neutral, (F) Neutral, MCID-W, (G) MCID- W, MCID-I, (H) MCID-W, Neutral, (I) MCID-W, MCID-W. Neutral patients did not achieve either MCID-I or MCID-W.

The final cohort consisted of 59 staged BTKA patients. In patients who achieved MCID-I in the first TKA, 39.1% achieved MCID-I again in the second TKA (A), 39.1% were neutral (B), and 21.7% achieved MCID-W (C) in the second TKA. However, 77.8% of those who achieved MCID-W in the first joint (n = 9) went on to achieve MCID-I (G) in the second TKA. Those who achieved MCID-I after both TKAs (A) had a longer staged interval than those who achieved first MCID-I, then MCID-W (C) (15 months vs 8 months, P = 0.0113).

In staged BTKA, MCID achievement of the first TKA may not be associated with the outcome of the second TKA.