Cartilage

Several methodological comparisons have been made regarding quantitative radio graphic data generated by the OAI (Supplementary Table 2 online). The findings emphasize, for example, the need to take radio-anatomic alignment of OAI fixed-flexion radiographs into account when analyzing change in JSW, and the need for central radiographic readings. Regarding semiquantitative scoring of articular tissue pathology using MRI images, two existing systems—WORMS (whole organ MRI score) and BLOKS (Boston Leeds osteoarthritis knee score)—were applied to a sample of images of 113 knees with radiographic OA and at risk of progression, from the OAI cohort. Both methods were shown to be reliable cross-sectionally (Supplementary Table 2 online). Longitudinally, BLOKS was found to be superior to WORMS for assessment of change in the meniscus, and WORMS was superior to BLOKS for scoring bone-marrow lesions (BMLs), in terms of predicting cartilage loss.^{4 (link)} A new hybrid method (MOAKS; MRI OA knee score) was hence proposed with the aim of combining the advantages of each scoring system.^{5 (link)} In assessing which sequence is better to detect such changes, more and larger focal cartilage defects and BMLs were detected with the intermediate-weighted fat-suppressed spin echo sequence than with DESS^{6 ,7 (link)} (Figure 2, Supplementary Table 2 online).
Semi-automated segmentation algorithms for quantitative measurement of cartilage, bone, meniscus, and thigh muscles (Figure 3) have been assessed. These studies have used different image analysis approaches and have reported, in part, the level of agreement with manual segmentation and/or the level of inter-observer reliability (Figure 1, Supplementary Table 2 online).
The sensitivity to change of cartilage thick ness over 1 year in the medial femorotibial compartment was found to be similar between sagittal DESS, coronal multiplanar reconstructed DESS, and coronal FLASH in 80 knees (Figure 2), with SRMs ranging from −0.34 to −0.38.^{8 (link)} The three protocols were also highly intercorrelated cross-sectionally (coefficient of correlation [r] ≥0.94); analysis of every second 0.7 mm DESS image provided similar sensitivity to change as analysis of every image.^{8 (link)} Change in the medial weight-bearing femur substantially exceeded that in the posterior aspect of the femoral condyle, suggesting that structural progression is faster in (commonly) weight-bearing regions of the joint.^{9 (link)}Measuring between-group differences using cartilage subregions (Figure 4) or atlases of cartilage thickness within anatomically defined cartilage plates has also been explored by several groups, alongside assessing whether such methods improve sensitivity to change (Supplementary Table 3 online). These studies generally identified the central subregion of the weight-bearing medial femoral cartilage plate as the region of interest with the greatest rate of cartilage loss and sensitivity to change (Figure 4).

At sacrifice the operated knees (mid femur to mid tibia) of all mice, and non-operated knees from 3 animals, were harvested, and the skin and muscle removed. Specimens were fixed in 10% neutral buffered formalin for 24 hrs, decalcified for 3 days in 10% formic acid/5% formalin, and paraffin embedded. Serial 4μm sagittal sections were cut across the width of the medial femoro-tibial joint and mounted on superfrost plus glass slides (3 serial sections per slide) with heating at 85°C for 30 minutes then overnight at 55°C. Sections every 40μm were stained with 0.04% toluidine blue and counterstained with 0.1% fast green (12–15 slides per mouse).
Two observers (CBL, AB) blinded to genotype and post-operative time, scored cartilage aggrecan loss (0–3) and structural damage (0–7), with maximal and summed score (sum of all scores in all slides) recorded as previously described (7 (link)). Each slide received a single score for each parameter representing the maximal score in the three sections on the slide. The number of slides with scores for structural damage was recorded as a measure of the “stage” of OA (width of joint affected). The presence or absence of morphological chondrocyte hypertrophy (enlarged chondrocyte lacunae with lack of toluidine blue stain around a collapsed cell as typically observed in the growth plate or calcified cartilage) in the non-calcified articular cartilage was recorded. Osteophyte size (0 = none, 1 = small ~ the same thickness as the adjacent cartilage, 2 = medium ~ 1–3 × the thickness as the adjacent cartilage, 3 = large >3 × the thickness as the adjacent cartilage) and osteophyte maturity (0 = none, 1 = predominantly cartilaginous, 2 = mixed cartilage and bone with active vascular invasion and endochondral ossification, 3 = predominantly bone) were scored on coded digital images of the same location of the anterior-medial tibia in each animal.