MRI Osteoarthritis Knee Score (MOAKS)

Last revised by Henry Knipe on 11 Mar 2020

MRI Osteoarthritis Knee Score (MOAKS) is a semi-quantitative scoring tool that was developed from the Whole Organ Magnetic Resonance Imaging Score (WORMS) and Boston Leeds Osteoarthritis Knee Score (BLOKS) scoring tools. MOAKS has been shown to have very good to excellent reliability. 



Fourteen subregions are defined for scoring of articular cartilage and bone marrow lesions 1:

  • patella (axial view)
    • medial patella (including median patellar ridge)
    • lateral patella
  • femur
    • medial and lateral trochlea
    • medial and lateral central femur
    • medial and lateral posterior femur
  • tibia
    • anterior, central and posterior medial articular cartilage
    • anterior, central and posterior lateral articular cartilage
    • subspinous region (tibial spines)

N.B. lesions crossing two subregions are scored in both subregions

Individual features
Bone marrow lesions and cysts
  • bone marrow lesion: ill-defined trabecular bone signal that is low on T1 and high on T2FS weighted imaging
  • cyst: well-defined regions of fluid signal adjacent to the subchondral bone plate
  • multiple bone marrow lesions in one subregion are collated into one percentage
  • scoring
    • subregional volume of bone marrow lesion (including cysts)
      • grade 0: none
      • grade 1: <33%
      • grade 2: 33-66%
      • grade 3: >66%
    • % of lesion that is bone marrow lesion vs cyst
      • grade 0: none
      • grade 1: <33%
      • grade 2: 33-66%
      • grade 3: >66%
Articular cartilage

Articular cartilage is graded for lesion size (any cartilage loss) and degree of full-thickness loss:

  • size of cartilage loss as a percentage of subregion size
    • grade 0: none
    • grade 1: <10%
    • grade 2: 10-75%
    • grade 3: >75%
  • percentage of full-thickness cartilage loss in subregion
    • grade 0: none
    • grade 1: <10%
    • grade 2: 10-75%
    • grade 3: >75%

Osteophytes are graded in 12 regions as none (grade 0), small (grade 1), medium (grade 2) or large (grade 3):

  • anterior femur (trochlea): medial and lateral (sagittal/axial)
  • posterior femur: medial and lateral (sagittal/axial)
  • central femur: medial and lateral (coronal)
  • patella: superior, inferior (sagittal) and medial, lateral (axial)
  • tibia: medial and lateral (coronal)
Hoffa's synovitis and synovitis-effusion

Mild chronic synovitis in MOAKS is described as diffuse high signal on T2/PD FS sequences within Hoffa's fat pad. It is scored on the sagittal view as:

  • grade 0: normal
  • grade 1: mild
  • grade 2: moderate
  • grade 3: severe

Effusion-synovitis is scored on the axial view as:

  • grade 0: physiological volume
  • grade 1: small - fluid continuous in the retropatellar space
  • grade 2: medium - slight convexity of the suprapatellar bursa
  • grade 3: large - evidence of capsular distension

Meniscal position and morphology are graded. Meniscal extrusion is graded as <2 mm (grade 0), 2-2.9 mm (grade 1), 3-4.9 mm (grade 2), and >5 mm (grade 3) and scored in four locations:

  • medial meniscus
    • medial extrusion relative to medial tibial margin (coronal)
    • maximal anterior extrusion (sagittal)
  • lateral meniscus
    • lateral extrusion relative to lateral tibial margin (coronal)
    • maximal anterior extrusion (sagittal)

Morphology is scored at the anterior and posterior horns (sagittal) and body (coronal) for both medial and lateral menisci. The following features are scored as present (yes) or absent (no):

  • signal not extending through to meniscal surface on at least two slices
  • vertical tear (radial and longitudinal): must extend to both femoral and tibial surfaces
  • horizontal and radial tear: must extend from the periphery to either femoral or tibial surface
  • complex tear: ≥3 point involvement of the tibial and femoral surfaces
  • root tear
  • partial maceration
  • progressive partial maceration'
  • complete maceration
  • meniscal cyst
  • meniscal hypertrophy

The following are scored:

  • anterior cruciate ligament
    • normal vs complete tear
    • associated bone marrow lesion/cyst at site of insertion or origin
    • anterior cruciate ligament repair
  • posterior cruciate ligament
    • normal vs complete tear
    • associated bone marrow lesion/cyst at site of insertion or origin
  • patellar tendon
    • normal signal vs signal abnormality
Periarticular features

The following structures are defined as being absent or present:

  • pes anserine bursitis
  • iliotibial band signal
  • popliteal (Baker's) cyst
  • infrapatellar bursa signal
  • prepatellar bursa signal
  • ganglion cyst
    • associated with the tibio-fibular joint
    • associated with the cruciate ligaments
    • other
  • loose bodies

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