This basic science tip comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.
Early cartilage changes in early-stage osteoarthritis (OA) often exist before symptoms arise. Using MRI, researchers assessed a random sample of 73 subjects, aged 40 to 79 years and without knee pain, for cartilage changes.1 A self-reported BMI at age 25, a current measured BMI, and change in BMI were recorded. Knee cartilage was scored semi-quantitatively (grades 0 to 4) on MRI. In primary analysis, cartilage damage was defined as ≥2 (at least moderate), and in a secondary analysis as ≥3 (severe). Researchers also conducted a sensitivity analysis by dichotomizing current BMI as <25 vs. ≥25. Logistic regression was used to evaluate the association of each BMI variable with prevalent MRI-detected cartilage damage, adjusted for age and sex.
Their abstract states that among the 73 subjects, knee cartilage damage ≥2 and ≥3 was present in 65.4% and 28.7%, respectively. Note the high prevalence. The median current BMI was 26.1, while the median past BMI was 21.6. For cartilage damage ≥2, current BMI had a non-statistically significant odds ratio (OR) of 1.65 per 5-unit increase in BMI (95% CI 0.93-2.92). For cartilage damage ≥3, current BMI showed a trend towards statistical significance with an OR of 1.70 per 5 units (95% CI 0.99-2.92). Past BMI and change in BMI were not significantly associated with cartilage damage. Current BMI ≥ 25 was statistically significantly associated with cartilage damage ≥2 (OR 3.04 [95% CI 1.10-8.42]), but not with damage ≥3 (OR 2.63 [95% CI 0.86-8.03]).
The take-home is that MRI-detected knee cartilage damage is highly prevalent in asymptomatic populations aged 40 to 79 years. There is a trend towards significance in the relationship between rising BMI and cartilage damage severity. (It should be added there are localities where a BMI of 26.1, which is technically in the “overweight” zone, would be considered relatively low.) Although this study lends some support to the relationship between BMI and the pathogenesis of knee cartilage damage in asymptomatic people, the role of BMI in symptomatic OA progression is clearer.
In another study, researchers showed that weight loss over 48 months among obese and overweight individuals is associated with slowed knee cartilage degeneration and improved knee symptoms.2 These results point to a promising approach to disease modification that carries little or no risk.
References
- Keng A, Sayre EC, Guermazi A, Nicolaou S, Esdaile JM, Thorne A, Singer J, Kopec JA, Cibere J. Association of body mass index with knee cartilage damage in an asymptomatic population-based study. BMC Musculoskelet Disord. 2017 Dec 8;18(1):517. doi: 10.1186/s12891-017-1884-7. PMID: 29221481 PMCID: PMC5723095
- Gersing AS, Solka M, Joseph GB, Schwaiger BJ, Heilmeier U, Feuerriegel G, Nevitt MC, McCulloch CE, Link TM. Progression of cartilage degeneration and clinical symptoms in obese and overweight individuals is dependent on the amount of weight loss: 48-month data from the Osteoarthritis Initiative. Osteoarthritis Cartilage. 2016 Jul;24(7):1126-34. doi: 10.1016/j.joca.2016.01.984. PMID: 26828356 PMCID: PMC4907808
