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| Imaging technique | Working principle | Pros | Cons | Detectable OA features | Grading scale |
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| X-ray imaging/radiography/roentgenography | Ionizing radiation from X-ray passes through patient’s body in one direction | (i) Low cost | (i) Mostly limited to 2D visualization | (i) Joint space narrowing | (i) Kellgren–Lawrence (KL) |
| (ii) Routine OA imaging in clinical practice | (ii) Less sensitive to change over time | (ii) Osteophyte formation | (ii) Ahlbäck |
| (iii) Allows bony structure visualization | (iii) Lack of soft tissue visualization | (iii) Cyst formation | (iii) Brandt |
| (iv) Subjects can be scanned in different positions, including supine, sitting, standing, fully extended, semiflexed, non-weight-bearing, and weight-bearing conditions | (iv) Prone to positioning errors | (iv) Subchondral sclerosis | (iv) Osteoarthritis Research Society International (OARSI) |
| | (v) Risk of radiation | | (v) International Knee Documentation Committee (IKDC) |
| | (vi) Fair bank |
| | (vii) Jäger-Wirth |
|
| Magnetic resonance imaging (MRI) | Protons in patient’s body are stimulated using magnetic fields | (i) Permits visualization of intra-articular structures and soft tissues | (i) Expensive | (i) Joint space narrowing | (i) Modified Outerbridge classification |
| (ii) Permits visualization of cartilage biochemical properties and pathological features | (ii) Intolerable to metal implant | (ii) Bone marrow lesions | (ii) Whole-Organ MRI Scoring (WORMS) |
| (iii) Allows 2D and 3D visualization | (iii) Risk of overdiagnosis | | (iii) Knee Osteoarthritis Scoring System (KOSS) |
| | | | (iv) Boston Leeds Osteoarthritis Knee Score (BLOKS) |
| | | | (v) MRI Osteoarthritis Knee Score (MOAKS) |
|
| Computed tomography (CT) | Ionizing radiation is passed through patient’s body using motorized X-ray source before reaching the electronic detector | (i) Permits visualization of bony structure and calcified tissue (e.g., intra-articular calcium crystal deposition) | (i) Expensive | (i) Osteophyte formation | (i) OsteoArthritis Computed Tomography (OACT) |
| (ii) Allows study of osteoarthritic biomechanics using weight-bearing and kinematic four-dimensional CT | (ii) Risk of radiation | (ii) Cyst formation |
| (iii) Allows study of joint metabolism | (iii) Requires intra-articular injection of contrast material in the case of CT arthrography, may cause allergic reaction | (iii) Subchondral sclerosis |
| (iv) Potential image-guided therapy tools with CT arthrography | | |
| (v) Allows 2D (slices) and 3D visualization | | |
|
| Nuclear medicine bone scan | Radioactive tracer is injected into patient’s vein is absorbed by metabolically active cells and tissues | (i) Enables radiopharmaceutical localization | (i) Injection of radioactive tracer | (i) Osteophyte formation | Nil |
| (ii) Allows evaluation of injury status | (ii) Complicated procedures | (ii) Cyst formation |
| (iii) Differentiation of OA from bone metastases and osteomyelitis | (iii) No grading system for OA disease severity | (iii) Subchondral sclerosis |
| (iv) 2D and 3D visualization | | (iv) Bone marrow lesions |
|
| Ultrasonography | Knee joint is scanned with sound waves | (i) Low cost | (i) Limited to 2D visualization | (i) Osteophyte formation | (i) Ultrasonographic grading scale |
| (ii) Evaluation of ligaments and synovium | (ii) Poor contrast caused by fat and air |
| (iii) Real-time assessment | (iii) Limited to evaluation of the far inner margins of lateral and medial femorotibial joints |
| (iv) Portable | (iv) Risk of overdiagnosis |
| (v) Potential image-guided therapy tools | |
| (vi) Better spatial resolution | |
|
| Optical coherence tomography (OCT) | Cartilage sample is scanned with infrared light | (i) Evaluation of articular cartilage at resolution up to micron scale at 4 to 20 μm near real-time assessment | (i) Not applicable to in vivo assessment | (i) Cartilage surface roughness | (i) Degenerative joint disease (DJD) classification |
| (ii) Portable | (ii) Time-consuming | (ii) Degeneration of articular cartilage |
| (iii) Potential image-guided therapy tools | | |
| (iv) 2D and 3D visualization | | |
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