OARSI DMM Grade Osteoarthritic Methods

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Processing of Knee Joints for OARSI DMM Grade Osteoarthritic Methods

Knees are embedded in paraffin blocks in the frontal plane. A section is taken at the approximate mid-point of the knee and stained with toluidine blue (t. blue).

Evaluation of Joints

The following parameters are evaluated for each of the four surfaces (surface meaning the entire thickness of the cartilage, not just the outer surface) of the knee (medial tibial plateau, medial femoral condyle, lateral tibial plateau, lateral femoral condyle):

Grading of Osteoarthritic Cartilage Damage (OARSI Criteria)

0 = Normal

0.5 = Very Minimal Degeneration: Loss of t. blue (or other cationic dye) stain (proteoglycan loss) without structural changes

1 = Minimal Degeneration: Small surface to subsurface fibrillations without major loss of chondrocytes or cartilage matrix, may have small focal area of chondrocyte loss extending partial thickness over less than 5% of total surface

2 = Mild Degeneration: Vertical clefts down to the layer immediately below the superficial layer with few extending deeper and some loss of surface matrix, or focal areas of chondrocyte/proteoglycan loss with good collagen preservation extending partial thickness over 5 to 10% of the surface

3 = Moderate Degeneration: Vertical clefts/erosion to the calcified cartilage extending over <25% of the articular surface, or focal areas of chondrocyte/proteoglycan loss with some collagen preservation extending full thickness over 10 to 24% of the surface

4 = Marked Degeneration: Vertical clefts/erosion to the calcified cartilage extending over 25 to 50% of the articular surface, or focal areas of chondrocyte/proteoglycan loss with some collagen preservation extending full thickness over 25 to 50% of the surface

5 = Severe Degeneration: Vertical clefts/erosion to the calcified cartilage extending over 50 to 75% of the articular surface, or focal areas of chondrocyte/proteoglycan loss with some collagen preservation extending full thickness over 50 to 75% of the surface

6 = Very Severe Degeneration: Vertical clefts/erosion to the calcified cartilage extending >75% of the articular surface, may be few areas of acellular collagen remaining

If a surface is not in the section or not in the load bearing area then no score is given and NA is recorded.

Total Joint Cartilage Degeneration Sum

The sum of the cartilage degeneration scores for all four surfaces is calculated. The maximum value is 24.

Osteophyte Score and Measurement

The largest osteophyte (tibia or femur) is measured using an ocular micrometer. A score is assigned based on the measurement as follows:

1 = Small (up to 150 µm)
2 = Medium (151 to 300 µm)
3 = Large (>300 µm)

Total Joint Score

The total joint score is calculated by adding the medial and lateral osteophyte scores to the total joint cartilage degeneration sum. The maximum value is 30.

Supplemental Parameters (Not included in overall joint scores)

Measured Cartilage Degeneration

Cartilage damage (chondrocyte, proteoglycan and collagen matrix damage) and loss across all four surfaces is quantified by measuring (using an ocular micrometer) the total width of the following using an ocular micrometer. Measurements are expressed as a percentage of the total tibial or femoral surface width:

Any damage (proteoglycan loss or fibrillation ranging from superficial to full thickness loss).
Severe damage (total or near total loss of viable cartilage matrix to tidemark, >75% thickness)
Moderate damage or loss (extends thru 25 to 75% of the cartilage thickness)
Mild damage or loss (extends through 5 to 25% of the cartilage thickness)
Minimal damage (proteoglycan loss and/or minor surface fibrillations).

Bone Score (Medial tibia only, Indicative of load bearing differences between medial and lateral)

The extent of subchondral bone sclerosis/reduction in bone marrow area is scored as follows, in comparison to the lateral side of the joint:

0 = No increase
1 = Minimal (1 to 10% increase in bone mass/trabecular widths)
2 = Mild (11 to 25% increase in bone mass/trabecular widths)
3 = Moderate (26 to 50% increase in bone mass/trabecular widths)
4 = Marked (51 to 75% increase in bone mass/trabecular widths)
5 = Severe (>75% increase in bone mass/trabecular widths)

Instability Score (Indicative of response to surgical destabilization)

An instability score is assigned to indicate any proliferative changes in marginal zones, menisci (especially medial) or cruciate ligaments as follows:

0 = Normal
1 = Minimal to Mild
2 = Moderate
3 = Severe

Descriptive and Synovial Comments

Synovial reaction is described and characterized with respect to inflammation type and degree if present but not included in the score. Synovial/joint capsule/medial meniscal changes (inflammation and/or fibrosis) are described as minimal, mild, moderate, or severe if present and NSL if synovium is normal to further justify the instability score.