Why defining MCID matters in osteotomy outcomes
When patients undergo a corrective knee osteotomy—such as a medial opening-wedge high tibial osteotomy (OWHTO)—it is not enough to report that outcome scores improved. Clinicians and researchers need to know what magnitude of change is actually clinically meaningful for patients.
The concept of the Minimal Clinically Important Difference (MCID) addresses this: it is the smallest difference in a patient-reported outcome measure (PROM) that patients perceive as beneficial and that would justify a change in management. Having MCID thresholds helps evaluate the effectiveness of surgery, power clinical trials, and interpret PROM improvements.
How the study was conducted and what measures were used
This was a prospective observational cohort study of 196 patients who underwent isolated OWHTO with patient-specific cutting guides between January 2013 and January 2017.
Pre-operative scores and 2-year follow-up data were collected using three PROMs:
- Knee injury and Osteoarthritis Outcome Score (KOOS) — multiple subscales (Pain, Symptoms, ADL, Sport/Recreation, Quality of Life)
- Knee Society Score (KSS) — Symptoms and Activity components
- Short Form 12 (SF-12) — Physical Component Summary (PCS) and Mental Component Summary (MCS)
An anchor-based method was used to determine who achieved a “minimal change” vs “no change”: at 24 months patients answered a 5-point global question (“Compared with before surgery, how would you rate the operated joint now?”). Those who said “somewhat better” formed the minimal-change group; those who answered “about the same” or “somewhat worse” formed no-change. ROC curves were used to define cutoff scores that differentiated the groups.
What the results showed: MCID values and their interpretation
Key findings include:
- MCID values for the KOOS subscales:
- Pain: 15.4
- Symptoms: 15.1
- ADL: 17.0
- Sport/Recreation: 11.2
- Quality of Life: 16.5
- MCID values for KSS:
- Symptoms: 3.0
- Activity: 5.6
- MCID values for SF-12:
- Physical Component (PCS): 7.2
- Mental Component (MCS): 6.3
- All PROMs showed significantly greater improvement in the minimal-change group vs no-change group at 2 years.
How this informs clinical practice and research
These MCID thresholds help clinicians and researchers in several ways:
- Interpreting individual patient outcomes: Knowing that a KOOS Pain improvement of ~15 points or an SF-12 PCS improvement of ~7 points is likely meaningful helps assess whether a given patient has achieved a clinically relevant benefit.
- Designing trials/power calculations: The MCID values provide benchmarks for sample-size calculation or defining responder criteria in studies of OWHTO.
- Benchmarking surgical performance: Surgeons may compare their cohort’s change in PROMs with these MCID values to assess whether their results meet meaningful thresholds.
- Patient counselling: Surgeons can provide patients with realistic expectations regarding how much improvement in PROMs is considered meaningful.
Key take-away messages
- After OWHTO, the study defined specific MCID values: e.g., ~15 points for KOOS Pain, ~17 points for KOOS ADL, ~7 points for SF-12 PCS.
- Achieving change above these thresholds is more likely to represent a meaningful benefit to the patient, not just statistical improvement.
- These thresholds may be used for outcome interpretation, study design and patient counselling—but they are specific to OWHTO with PSCGs and may not apply to other techniques or populations without validation.
- As a Level II prospective cohort study, the findings are credible but future studies should validate the MCID in different patient groups, longer follow-up durations, and other osteotomy techniques.
Link to full paper: Evaluation of the “Minimal Clinically Important Difference” (MCID) of the KOOS, KSS and SF-12 scores after open-wedge high tibial osteotomy
Sources used in report overview:
