New insights into sex differences in knee JOINT anatomy and osteoarthritis

Women are more frequently affected by knee osteoarthritis than men, but the biological and structural reasons for this difference are still not fully understood. Two recent publications involving Chondrometrics contribute new evidence to this question by focusing on sex-related differences in MRI knee cartilage thickness, radiographic joint space width (JSW), imaging of other articular tissues, and potential treatment response.

The first study, led by Spoelder and colleagues (left infographic), directly addressed a key methodological challenge in this field: Are women’s thinner knee cartilages simply a consequence of smaller body size, or do genuine sex-related differences remain after accounting for height, body mass index, and age?

Using data from the Osteoarthritis Initiative, the authors selected 63 male–female pairs without radiographic knee osteoarthritis or OA-related symptoms. Each pair was closely matched for the above confounding demographic variables. Femorotibial cartilage thickness was then assessed using two complementary MRI-based approaches: conventional compartmental cartilage thickness analysis by Chondrometrics, and three-dimensional cartilage surface mapping.

The findings were clear. Even after matching for body size, men had significantly thicker cartilage than women in both the medial and lateral femorotibial compartments (about 12%). Surface mapping revealed that the sex-related differences were not uniform across the joint surfaces but particularly pronounced in specific regions, with the largest difference was observed in the trochlea (16%).

These results strengthen the evidence that sex-related differences in cartilage thickness likely represent genuine biological differences in joint anatomy and could contribute to the higher prevalence of knee osteoarthritis in women. The authors emphasize that articular surface anatomy is only one part of a larger picture, which likely also includes biomechanics, hormonal factors, bone shape, genetics, and other biological mechanisms.

A perspective article by Eckstein (right infographic) places these findings into a broader conceptual and clinical framework. The review examines sex differences in cartilage anatomy, articular and peri-articular tissue imaging, and cartilage treatment response in osteoarthritis. It also distinguishes between “observed” and “genuine” sex differences that remain after adjustment or matching for relevant covariates, particularly as body height.

The perspective confirms that men generally display greater radiographic JSW (and cartilage thickness) than women. Yet, while sex differences in “radiographic JSW” become smaller, disappear, or even reverse with more severe radiographic disease status (increasing joint space narrowing = JSN grade), sex differences in “cartilage thickness” persist even in more advanced disease stages, although at somewhat reduced level. This discordance points to the important role of other tissues, most likely the meniscus, in radiographic measures of knee osteoarthritis. These results are important in context of patient inclusion in clinical trials (overrecruiting of men if a minimum JSW measure is required) and prognosis based on baseline JSW.

In an exhaustive table, the review highlights sex differences in other articular and peri-articular tissues, including the meniscus, bone, adipose tissue, and others. Interestingly also, female joint surface areas remained significantly smaller than those of men after 1:1 matching of anthropometry. This means female knees with encounter consistently greater joint loads than those of males matched for body height, BMI, and age and are hence exposed to greater proportional mechanical challenges.

Beyond anatomy and imaging, the review raises an additional forward-looking question: Could sex also influence response to cartilage-directed therapies? Preliminary findings suggest that men may show stronger structural responses to surgical (knee joint distraction) and pharmacological (anabolic cartilage) therapy, although these observations require further investigation.

For Chondrometrics, the two publications underline the value of quantitative MRI-based cartilage analysis for detecting subtle but meaningful differences in joint structure. They also reinforce the importance of considering sex as a biological variable in osteoarthritis research, clinical trial design, and future approaches to diagnosis, prognosis, and therapy monitoring.

Taken together, the two papers move the discussion beyond the usual “women have more knee OA” observation. Whereas Spoelder et al. showed that women have thinner femorotibial cartilage, even when age and body size are carefully matched, the review by Eckstein then adds an even more uncomfortable anatomical punchline: Smaller joint surface areas in women may mean that load is carried over a smaller contact architecture, potentially increasing mechanical stress where it matters most. So the message is not simply that female knees have “less cartilage”. They may, in a very real anatomical sense, have less room to share the load. That makes sex not a checkbox in OA research, but a structural variable.