Multimodality imaging considerations for genicular artery embolization in knee osteoarthritis

Table 1 Kellgren-Lawrence radiographic grading system for knee osteoarthritis

Grade	Description
0	No radiographic features of osteoarthritis
1	Doubtful joint space narrowing and possible osteophytic lipping
2	Definite osteophytes and possible joint space narrowing
3	Moderate multiple osteophytes, definite joint space narrowing, some sclerosis, and possible bone deformity
4	Large osteophytes, marked joint space narrowing, severe sclerosis, and definite bone deformity

Table 2 Comparison of semiquantitative magnetic resonance imaging scoring systems for knee osteoarthritis relevant to genicular artery embolization (whole-organ magnetic resonance imaging score, Boston-Leeds osteoarthritis knee score, and magnetic resonance imaging osteoarthritis knee score)

Feature	WORMS	BLOKS	MOAKS
Primary goal	Whole-organ assessment across 14 knee subregions	Focuses on lesion detail	Unified system integrating the best aspects of WORMS and BLOKS
Synovitis assessment	Combined score for effusion and synovitis; did not separately quantify them	Separated effusion from Hoffa’s fat pad synovitis	Dual scoring: Evaluates Hoffa’s fat pad synovitis and effusion-synovitis separately (0-3 scale)
BMLs	Graded by size in various subregions	More granular scoring for BML size and number	Simplified grading (0-3) by size with a clearer, more reproducible definition
Meniscal damage	Combined tear types and extrusion into one metric	More detailed evaluation, including hypertrophy and maceration	Improved percentage-of-area scoring to enhance sensitivity to small changes. Meniscal damage is scored by tear/maceration status and extent in each meniscal subregion, with separate assessment of meniscal extrusion (0-3 scale for extrusion)
Reliability	Good but not perfect; some features overlap	Improved inter-reader reliability for specific features	Highest clinical adoption; achieves substantial-to-excellent agreement (Kappa 0.61-1.0)
GAE application	Used to summarize whole-joint MRI disease burden in GAE cohorts. Can support prognostic modeling when WORMS subscores are used as imaging inputs	Useful for separating synovial membrane thickening from joint fluid on non-contrast MRI. Supports synovitis-phenotype characterization relevant to GAE candidate selection	Supports characterization of the synovitis-phenotype. Provides a standardized framework for candidate selection. Correlates baseline synovial/cartilage health to clinical pain response

WORMS: Whole-organ magnetic resonance imaging score; BLOKS: Boston-Leeds osteoarthritis knee score; MOAKS: Magnetic resonance imaging osteoarthritis knee score; BMLs: Bone marrow lesions; GAE: Genicular artery embolization; MRI: Magnetic resonance imaging.

Table 3 Genicular artery anatomy and common variants

Artery	Typical origin	Common variants
Superior lateral	Popliteal artery	Early branching, accessory vessels
Superior medial	Popliteal artery	Shared origin with DGA from SFA
Inferior lateral	Popliteal artery	Origin from anterior tibial artery
Inferior medial	Popliteal artery	Multiple branches, anastomoses
Descending genicular	SFA (adductor canal)	Shared origin with SMGA

SFA: Superficial femoral artery; DGA: Descending genicular artery; SMGA: Superior medial genicular artery.

Table 4 Expected post-genicular artery embolization imaging findings by follow-up interval (0-12 months)

Modality	0-1 month (early)	1-3 months (intermediate)	6-12 months (long-term)
Radiography (X-ray)	No structural response expected. Primary role is safety to exclude fracture or rapid collapse	OA hallmarks (osteophytes, joint space narrowing) remain unchanged; not considered a response biomarker	Useful mainly for longitudinal progression tracking in research cohorts
MRI	May show decreased synovial enhancement transient subchondral marrow signal abnormalities may be seen early and warrant interval reassessment	Most consistent imaging response window: Decreased synovial enhancement/thickness; Effusion-synovitis often trends downward	Reduced synovitis generally persists; cartilage loss and osteophytes remain stable and non-reversible

MRI: Magnetic resonance imaging; OA: Osteoarthritis.

Table 5 Post-genicular artery embolization imaging interpretation guide for knee osteoarthritis showing expected response patterns

Category	Imaging findings and interpretation
Expected response patterns	Reduced synovial enhancement on contrast-enhanced MRI. Reduced synovial thickness/volume. Lower effusion-synovitis grade when scored. Interval normalization of early marrow signal changes when present

This table highlights expected post-procedural imaging response patterns, meaning findings that generally reflect treatment-related improvement in inflammation-predominant disease on follow-up imaging. These include reduced synovial enhancement on contrast-enhanced magnetic resonance imaging, decreased synovial thickness or volume, lower effusion-synovitis grade when scored, and interval normalization of early marrow signal changes when present. MRI: Magnetic resonance imaging.

Table 6 Post-genicular artery embolization imaging interpretation guide for knee osteoarthritis showing common pitfalls

Category	Imaging findings and interpretation
Interpretive pitfalls	Persistent osteophytes should not be interpreted as treatment failure. Static cartilage defects should not be interpreted as treatment failure. No change in joint space narrowing on radiography does not exclude clinical response. Early focal T1-hypointense subchondral signal should not be labeled osteonecrosis without follow-up

This table highlights interpretive pitfalls, meaning findings that may persist or fluctuate after genicular artery embolization and should not be automatically overcalled as treatment failure or irreversible complication without clinical correlation and interval comparison. These include persistent osteophytes, unchanged cartilage defects, no radiographic change in joint-space narrowing, and early focal subchondral T1-hypointense signal that should not be labeled osteonecrosis without follow-up assessment.