Body mass index linked to knee structural changes in 33-year-olds

Mild structural changes visible in knee MRI scans are already common among adults in their thirties - even in those without knee pain or other symptoms. A study by the University of Oulu found signs of joint damage in more than half of the 33-year-old participants. A high body mass index emerged as the most common factor associated with these changes.

The participants were part of the Northern Finland Birth Cohort 1986 (NFBC1986), with 297 individuals undergoing knee imaging. Each participant received a comprehensive health examination, provided blood samples, and underwent a magnetic resonance imaging scan of the knee. Their average age was 33.7 years.

The most common findings were minor articular cartilage defects, particularly between the kneecap and thighbone, observed in over half of those imaged. Cartilage defects were also found in the joint between the shinbone and thighbone in about a quarter of participants. In addition, small bone spurs, or osteophytes, were detected in more than half of the group, although these were generally small.

Researchers identified a higher body mass index as the clearest factor linked to the MRI findings.

Weight in particular seems to be associated with structural changes in the knee joint, as height had a much smaller effect compared to body mass index. These results highlight the importance of weight management in preventing joint diseases."

Joona Tapio, specialist trainee doctor and researcher at the Faculty of Biochemistry and Molecular Medicine

"The use of knee MRI is increasing, often for very good reasons. Modern imaging technologies reveal even minor osteoarthritis-like changes. As with lumbar spine imaging, it is crucial to interpret knee findings within the broader clinical context and to adhere to appropriate imaging guidelines," says Antti Kemppainen, radiologist and researcher at the Faculty of Medicine.

Although most participants were asymptomatic, the findings suggest that structural changes in joints can occur before clear symptoms develop. The researchers stress the need for longitudinal studies to determine which factors predict the progression of these changes later in life.

The study was published in Osteoarthritis and Cartilage in April: Kemppainen A, Tapio J, Nieminen MT, Saarakkala S, Nevalainen MT. Structural knee MRI findings are already frequent in a general population-based birth cohort at 33 years of age. Osteoarthritis Cartilage. 2025 Apr 17.