Higher fat mass and increased body mass index (BMI) adversely affected hip cartilage in women, while increases in fat-free mass were associated with beneficial cartilage changes at the hip for women and men, according to an Australian community-based study.

After adjusting for age and femoral head bone area, for every 1-unit increase in BMI, there was an associated 26 mm³reduction in femoral head cartilage volume in women, although no such link was seen in men for BMI and femoral head cartilage volume, reported Flavia M. Cicuttini, MD, of Monash University in Melbourne, in colleagues.

The results “likely represent very early structural joint damage” given that the study population had no clinical hip disease, the investigators wrote in Arthritis Research and Therapy,

However, they added that “the mechanisms by which an increased BMI and fat mass adversely affects hip cartilage is unknown. It is possible that deleterious structural changes may in part be due to excessive loading of the hip joint caused by increased body mass. For instance, through altered joint biomechanics, obesity may remodel hip bone. In turn, abnormal bone geometry could act as an intermediary between obesity and cartilage damage.”

The group evaluated BMI and body composition in 141 participants (62 men, 79 women), ages 50 to 85, without hip osteoarthritis (OA) who took part in the Melbourne Collaborative Cohort Study (MCCS). Participants had an MRI exam done of their dominant hip an average of 16.9 years after MMCS entry.

Femoral head cartilage volume was measured and femoral head cartilage defects were scored in central, anterior, and femoral regions.

The prevalence of cartilage defects in the anterior region of the femoral head was 6.5% in men and 1.2% in women, and the prevalence of cartilage defects in the posterior region was 17.7% in both men and women. The median of the total Western Ontario and McMaster University Osteoarthritis Index (WOMAC) pain score was 19 for men and 22 for women (of a possible 500).

Greater fat mass (beta -11 mm³, 95% CI -21 to -1 mm³, P=0.03) and percentage body fat (beta -13 mm³, 95% CI -26 to -0 mm³,P=0.04) at baseline were both associated with reduced femoral head cartilage volume in women, after adjusting for age, femoral head bone area, and fat free mass, the authors reported.

Fat-free mass at baseline was positively associated with femoral head cartilage volume in men (beta 40 mm³, 95% CI 6-74 mm³, P=0.02) but not in women (beta 0 mm³, 95% CI -29 to 29 mm³, P=0.98), after adjusting for age, femoral head bone area, and fat-free mass.

Increased fat free mass at baseline was associated with a reduced risk for prevalent cartilage defects in the central superolateral region of the femoral head in women (OR 0.82, 95% CI 0.67-0.99, P=0.04) but not in men (OR 1.02, 95% CI 0.93 to 1.11, P=0.70) after adjusting for age, femoral head bone area, and fat mass.

Increased fat mass at baseline was associated with an increased risk of cartilage defects in the central superolateral region of the femoral head in women (OR 1.08, 95% CI 1.00-1.15, P=0.04) but not in men (OR 0.99, 95% CI 0.91-1.06,P=0.71), after adjusting for age, femoral head bone area, and fat-free mass.

“As BMI is an indirect and surrogate measure that cannot discriminate adipose from non-adipose mass, we also examined the association of body composition and found that measures of adiposity (fat mass and percentage of body fat) were associated with reduced femoral head cartilage volume for females, but not males,” the authors wrote.

The finding that increased fat-free mass reduced the risk for prevalent hip cartilage defects in women and increased femoral head cartilage volume in men, may mean “increased muscle mass promotes joint stability and protects against deleterious cartilage changes,” they add. “Nevertheless, this study has only examined total fat free mass and has not investigated local muscle mass.”

There were some study limitations. The inclusion of more men may have clarified the gender differences in the relationships between obesity and body composition measures and femoral head cartilage properties, the group stated.

Also, radiographs were not performed, and some participants may have had early radiographic OA, although median scores on the WOMAC pain index were very low, indicating a population without significant hip pain), they pointed out.

Additionally, BMI does not capture body composition changes that may occur with aging, and future studies with longitudinal body composition data are required.

“Finally, it has been notoriously difficult in epidemiological studies to assess structural changes at the hip joint using MRI,” the authors wrote. “Our division of the anterior, central and posterior regions was adapted from methods used by previously published works with smaller sample sizes, but these previous works provided no prevalence data of regional structural abnormalities for comparative purposes.”

They called for additional researcher to determine if modifying body composition alters the natural history of hip OA.

• Reviewed by Henry A. Solomon, MD, FACP, FACC Clinical Associate Professor, Weill Cornell Medical College and Dorothy Caputo, MA, BSN, RN, Nurse Planner

last updated 05.12.2015