IKDC Subjective Knee Form: complete clinical guide
Scoring formula, reference values, pre- and post-ACL application and clinical interpretation of the IKDC with free online calculator.
What is the IKDC Subjective Knee Form?
The IKDC Subjective Knee Form (International Knee Documentation Committee) was developed in 2001 by Irrgang et al. as a standardised patient-reported outcome instrument for knee injury patients. It is the most widely used outcome questionnaire globally in ACL, meniscus and chondropathy research.
Unlike the Lysholm — which evaluates specific domains with fixed weights — the IKDC measures the patient's global perception of symptoms, function and ability to return to activities.
ACL, PCL, collateral ligament and meniscal injuries, chondropathy, osteoarthritis and post-partial arthroplasty. Primary endpoint in international clinical trials.
Structure: 18 items across 3 domains
| Domain | Items | What it assesses |
|---|---|---|
| Symptoms | Q1–Q7 | Pain at rest, on stairs, squatting, stiffness, swelling |
| Sports and daily activities | Q8–Q16 | Gait, stairs, impact activities, sports |
| Current knee function | Q17–Q18 | Global patient rating on a 0–10 scale |
Each item uses an ordinal scale of 2 to 11 response options. Raw values are transformed into a 0–100 score using the official formula.
Calculate the IKDC for free
Apply the questionnaire online and get the score with exportable PDF.
Scoring formula
0 = maximum limitation | 100 = full function without symptoms
If any question is unanswered, the score is invalid. ISAKOS does not recommend missing data imputation for the IKDC.
Interpretation and reference values
| IKDC Score | Normative reference | Clinical context |
|---|---|---|
| 90–100 | Healthy knee | No limitation for competitive sports |
| 75–89 | Excellent post-ACL | Return to sport without restriction at 6–9 months |
| 60–74 | Good recovery | Limitations in high-impact sports |
| 45–59 | Moderate recovery | Daily activities preserved, sports limited |
| <45 | Unsatisfactory recovery | Significant functional limitation |
Healthy adults aged 20–40 without knee injury score between 89 and 94 points on average (Nwachukwu et al., 2020).
Clinical application: pre- and post-ACL
| Timepoint | Purpose | Expected score |
|---|---|---|
| Pre-operative | Functional baseline | 30–55 pts |
| 3 months post-op | Early progression | 45–65 pts |
| 6 months post-op | Return-to-sport criterion | ≥ 65 pts |
| 12 months post-op | Final functional outcome | 75–85 pts |
| 2+ years | Long-term follow-up | 80–90 pts |
Patients who reach IKDC ≥ 65 before return to sport have an 84% lower re-rupture risk (Grindem et al., BJSM 2016).
MCID and clinically relevant change
| Study | MCID | Population |
|---|---|---|
| Ingelsrud et al. (2018) | 11.5 pts | ACL |
| Schmitt et al. (2004) | 6.3–11.3 pts | Mixed |
| Ogura et al. (2022) | 9.2 pts | Post-meniscus |
In clinical practice, an improvement of ≥ 10 points between assessments is considered clinically relevant for most knee conditions.
References
- 1. Irrgang JJ, Anderson AF, Boland AL, et al. “Development and validation of the International Knee Documentation Committee Subjective Knee Form.” Am J Sports Med, 2001;29(5):600–613.
- 2. Grindem H, Snyder-Mackler L, Moksnes H, et al. “Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction.” Br J Sports Med, 2016;50(13):804–808.
- 3. Nwachukwu BU, Chang B, Fields K, et al. “Defining the patient acceptable symptom state for the IKDC, KOOS, and WOMAC.” Am J Sports Med, 2020;48(5):1129–1136.