Table 2.

Imaging techniques for knee OA diagnosis.

Imaging technique	Working principle	Pros	Cons	Detectable OA features	Grading scale
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