Linking Osteoarthritis and Obesity with the Right Imaging

Prof. Mikael Boesen, IAG’s Lead for Musculoskeletal Clinical Research and his team have published a comprehensive review on the association between weight loss and hip/knee osteoarthritis (OA) worsening, ‘The effects of weight loss on imaging outcomes in osteoarthritis of the hip or knee in people who are overweight or obese: a systematic review,’ in Osteoarthritis and Cartilage, 28(2020).

The paper evaluates joint structural changes in a weight-loss group and stable-weight group, using imaging techniques together with qualitative or quantitative scoring systems. The paper answered the following key question:

1. What is the effect of weight loss on imaging outcomes in OA of the hip or knee in people who are overweight or obese?
2. Which structural joint pathologies have been examined in OA weight loss studies?
3. Which outcome measurement instruments (OMIs) have been used in the assessment of structural OA changes, and what were the reported performance metrics?

This review highlighted the discrepancies between results depending on the imaging technique used and its associated scoring system.

The most widely imaging technique was MRI assessed with qualitative or quantitative scoring system. The qualitative scores showed inconclusive relationship between weight and OA improvement, making them less suitable as OMIs when evaluating the effect of weight loss on knee/hip OA progression. On the other hand, the use of quantitative scoring systems on MRI images lead to more concordant data in between studies.

The use of 3T MRI and T2 relaxation time mapping and Gadolinium-Enhanced MRI Cartilage (dGEMRIC) both concluded that weight loss improved cartilage quality. The few discordances found in these studies could be explained by differences in methodology. For instance, in the dGEMRIC studies, some groups chose intravenous gadolinium injection, whilst others preferred intra-articular, which led to disagreement on which compartments were most significantly affected.

The review brings to light an opportunity to correctly exploit modern imaging and quantitative assessments with the weight loss and further explore its impact on the cartilage loss and quality.

X-Ray + Joint Space Width (JSW)

Three of the 14 studies have used X-Ray as their imaging technique, which is widely used in the healthcare system to assess OA. The images were quantitatively assessed using Joint Space Width (JSW), where a higher score suggests more severe cartilage degeneration. None of the studies using this method of assessment found any significant changes in JSW over time, between groups. It therefore suggests no association between weight loss and OA improvement. This indicates that JSW might not be suitable to evaluate the effects of weight loss on joint structure for reasons, such as repositioning errors when measuring or difficulty distinguishing between meniscus and cartilage on X-Ray images.

MRI + Qualitative scoring systems (WORMS and MOAKS)

Two studies used Whole-Organ MRI Score (WORMS), which gives a multi-feature, qualitative organ assessment. Scores were compared at different time points in each group, where a bigger score increase indicated disease progression. Unfortunately, the two studies had discrepant results. The first study reported, after 48-months follow up, that the weight loss group had smaller adjusted mean increase in their score when compared to the stable-weight group. The second study recorded no changes in score difference during their 96-months follow up.

The other scoring system used to evaluate MRI images was MRI Osteoarthritis Knee Score (MOAKS), which again unites multiple parameters like bone marrow lesions and cartilage/meniscal morphology. However, the one study using this score concluded that weight loss had no significant effect on joint structure. The use of these two qualitative scoring systems on MRI images showed inconclusive relationship between weight and OA improvement, making them unsuited outcome measurement instrument (OMI) when evaluating the effect of weight loss on knee/hip OA progression.

MRI + Quantitative scoring systems (T2 relaxation time and dGEMRIC)

Other groups have preferred quantitative scoring systems to evaluate structure change in the hip and knee joint.  The biochemical and biophysical changes in articular cartilage give it the potential to detect the earliest signs of damage non-invasively. T2 relaxation time of cartilage has been shown to be a sensitive parameter for evaluation of early degeneration in articular cartilage. Across multiple follow up periods, it has been observed that weight loss influenced T2 relaxation time and dGEMRIC images, suggesting weight loss could prevent extensive joint damage and disease progression.