From the Guidelines
MRI of the knee uses several diagnostic criteria and scales to evaluate injuries and conditions, including standardized scoring systems like the WORMS, MOAKS, or BLOKS for osteoarthritis evaluation, a grading system for ligament injuries, and classification systems for meniscal tears and cartilage damage. The diagnostic criteria for an MRI of the knee include:
- Standardized scoring systems like the WORMS (Whole-Organ Magnetic Resonance Imaging Score), MOAKS (MRI Osteoarthritis Knee Score), or BLOKS (Boston Leeds Osteoarthritis Knee Score) for osteoarthritis evaluation 1
- A grading system for ligament injuries, ranging from Grade 1 (mild sprain) to Grade 3 (complete tear)
- Classification systems for meniscal tears, including location (medial/lateral), pattern (horizontal, vertical, radial, complex), and extent
- The ICRS (International Cartilage Repair Society) scale for cartilage damage, ranging from Grade 0 (normal) to Grade 4 (exposed bone)
- Evaluation of bone marrow lesions by size and intensity These standardized criteria help ensure consistent interpretation across different radiologists and medical facilities, allowing for accurate diagnosis and appropriate treatment planning 1. Some studies have shown that MRI can diagnose the patterns and severity of bone marrow contusions that frequently have an association with the specific mechanisms of injury and can predict associated soft-tissue injuries 1. Additionally, MRI can change management from surgical to conservative in up to 48% of patients presenting with a locked knee, which is usually an indication for arthroscopic procedure 1. The specific criteria used may vary depending on the suspected condition, with specialized protocols for conditions like osteochondral defects, synovitis, or inflammatory arthropathies.
From the Research
Diagnostic Criteria for MRI of the Knee
The diagnostic criteria or scales used for an MRI of the knee include:
- Outerbridge score 2
- Noyes' score 2
- Whole Organ Magnetic Resonance Score 2
- Boston-Leeds Osteoarthritis Knee Score 2
- MRI Osteoarthritis Knee Score 2
- Kellgren-Lawrence radiographic scores 3, 4
MRI Grading Systems
Several MRI grading systems have been proposed for osteoarthritis of the knee, including:
- A practical MRI grading system for osteoarthritis of the knee, which provides high interobserver and intraobserver agreement 3
- MRI evaluation of knee osteoarthritis, which enables visualization of tissues that are not seen by radiography, including cartilage, meniscus, bone marrow lesions, synovitis, and muscles 5
Comparison of Imaging Techniques
Studies have compared the accuracy of radiographs, MRI scans, and arthroscopic assessment in grading knee osteoarthritis, finding that:
- Kellgren-Lawrence grading of radiographs was moderately correlated with Outerbridge grades from arthroscopy for the medial compartment of the knee 4
- MRI reporting of knee osteoarthritis was moderately correlated with Outerbridge grades in the medial compartment 4
- KL and MRI grading was moderately correlated for the medial compartment 4