In middle-aged people with mild radiographic osteoarthritis (OA), structural features changes do occur a little over a year, irrespective of patient’s weight loss status.

Osteoarthritis (OA) is a principal cause of disability and a more massive public health problem in the United States. Although, no definitive intervention exists to decrease the progression of OA, bariatric surgery in patients with severe obesity is known to provide the improvement in OA symptoms. Also, it reduces the pain, cartilage loss and exerts beneficial effects on cartilage composition.  The mean durable decrease in knee pain severity scores for all such patients is approximately 50%, with some patients experiencing remission of pain. Bariatric surgery may develop a model of an effective treatment for chronic knee pain.

Previous MRI-based studies proposed that two intra-articular structural features are associated with knee pain and its severity, synovitis and bone marrow lesions (BML). Further, studies have suggested that a reduction in synovial thickening or the volume of BML is associated with a decrease in knee pain severity.

Rationale behind the research:

No studies of patients with knee pain undergoing bariatric surgery investigated if pain improvement was accompanied by a decrease in synovial thickening or BML size.

Therefore, in the present study the authors assessed whether those experiencing substantial weight loss had changes in innervated knee structures or in cartilage.

Objective:

To confirm the effect of substantial weight loss on the structures linked with knee pain and in cartilage.

Study outcome measures:

• Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): Based on Angst et al., a reduction of 18% was considered the minimal clinically important difference (MCID) for the WOMAC pain subscale.
• Longitudinal change in BML, synovitis, and cartilage damage
• Longitudinal change in cartilage thickness

Time period: baseline, and 1-year follow-up

Study Outcomes:

• Longitudinal change in BML, synovitis, and cartilage damage: There were no significant changes in knees from baseline to follow-up in BML score (difference in score for largest BML = 0.04; 95% confidence interval [CI]: -0.12, 0.20), synovitis (difference = -0.03, 95% CI: -0.15, 0.09), or cartilage damage (difference = 0.04, 95% CI: -0.07, 0.15). Further, the change was not different between those who lost <20% vs. those who lost 20% of their weight. Similar null results were seen when we examined the sum scores for BML, synovitis and cartilage morphology across all knee sub-regions and when we limited analyses to knees with OA.
• Longitudinal change in cartilage thickness: Of sub-regions in the knee, there were no significant changes in thickness noted. Further, very little correlation between cartilage thickness change and weight change percentage, for both region-based and location-independent approaches was reported. The only predefined sub-regions that showed a statistically significant positive correlation with weight change percentage were the anterior medial and lateral tibial cartilage sub-regions (aMT and aLT). More weight loss was correlated with a relative thinning at aMTand aLT sub-regions. The rank-based correlation for the thickening score also suggested a weak positive relationship, in which less weight loss associated with more thickening. Linear regression models of these ordered values-based sum scores also suggested no significant association between the percentage of weight change and the thinning (coeff=0.01, 95% CI: -0.01, 0.04), thickening (coeff = 0.02, 95% CI: 0.00, 0.04), or total change sum scores (coeff = 0.00, 95% CI: -0.03, 0.02).
• Cartilage thickness change in each sub-region and its relation to weight loss on both a continuous (i.e., per 1% change in weight) and categorical (i.e., 20% weight loss at 1- year vs < 20%) scales was examined. The sub-regions showing statistically significant positive associations with weight change on a continuous scale included the aMT cartilage and cLT cartilage such that greater weight loss resulted in an increased cartilage loss in those who experienced thickness loss or a reduced cartilage gain in those who experienced cartilage gain.

This study showed that neither the anatomic structures in the knee that is innervated and possible sources of pain in OA (i.e., BML and synovitis) nor cartilage changed significantly at a time when subjects were experiencing both weight loss and knee pain reduction. Moreover, except for the aMT, aLT, and cLT cartilage subregions, thickness loss or gain measured quantitatively were not associated with weight loss of >20% or with percent weight change when measured on a continuous scale.

In general, a little effect of weight loss on structural features of OA was found in this study. One explanation could be that the sample size was small and that failure to find an effect of weight loss on BML, synovitis, cartilage damage and cartilage thickness loss represents a type 2 error. It may not be the case as the majority of knees in both weight loss groups (i.e., >20% vs. <20%) showed no change at all in structural findings. Further, the confidence bounds around the estimates were narrow, so that the mean change in BML could not have exceeded the upper 95% confidence bound of 0.2 (for a 0e3 score); for synovitis, 0.09 (0e3 score); for cartilage damage, 0.15 (a 0e9 score). For cartilage thickness measures, 95% confidence bounds were even narrower given the nearly universal absence of change over a 1-year period. Further, the usually marked reduction in knee pain after massive weight loss was reported. Even when the analyses were limited to knees with radiographic OA, the amount of change seen was minimal. There were very few patients with grade three disease to examine this subset in the present study. While this study report that weight loss led to a slight thinning of cartilage in two sub-regions, the aMT, and aLT, these are not major sub-regions affected by disease. Thus, the conclusiveness of these findings remain uncertain.  Many sub-regions were examined, and many analyses performed, making it possible, as expected, given multiple testing to find positive results by chance. It is noted that in early OA, cartilage swelling, and thickening may be the first pathologic changes of the disease and it is possible that these subregions were swollen or edematous before the weight loss occurred and that the thinning represents a return to a non-edematous state.

The finding from this study on the relationship between weight loss and BML is consistent with a previous study by Gudbergsen et al. that reported that changes in BML score during a 16-week weight loss program were not affected by changes in weight.

In conclusion, rapid reduction in pain with marked weight loss was seen but was not accompanied by the structural change in cartilage.