Weaker subchondral bone and thinner articular cartilage of the knee are associated with elevated baseline fracture risk independently of osteoarthritis risk factors

Summary

Knee osteoarthritis involves damaged bones beneath joint surfaces but how current bone health predicts future disease state is unclear. We discovered higher osteoporotic fracture risk (FRAX) was linked to compromised knee bone quality and thinner cartilage. Integrating FRAX into osteoarthritis care could identify who may develop worse disease outcomes.

Objectives

To examine how well fracture risk predicts subchondral bone and cartilage morphometry independently of osteoarthritis (OA) clinical risk factors.

Methods

Male and female participants in the Osteoarthritis Initiative (OAI) at visit 5 (36 months) were evaluated for fracture risk using FRAX and categorized into low-, moderate-, or high-risk groups. These groups were compared for bone marrow lesion (BML) size, number and effusion, subchondral bone structure, density, and cartilage morphometry in the most affected knee at either same time point, 1 or 2 years later, using general linear models. Sex interactions were examined in each case and probed if significant.

Results

Among 1240 participants (58.8% female, age: 63.7 ± 8.8 years, and BMI: 30.1 ± 4.9 kg/m²), 20.32% had moderate or high FRAX and showed lower subchondral bone density (− 0.12 to − 0.25 g/cm²), less intact trabeculae, and thinner cartilage (− 0.14 to − 0.47 mm) compared to low FRAX (p < 0.05). Males showed larger positive FRAX correlations with bone density, and females had protective effects of FRAX against BML numbers, although the effects were small (sex interaction, p < 0.05). All FRAX models adjusting for OA risk factors yielded better model fit than OA risk factors alone. Having moderate/high versus low FRAX at baseline predicted a 1.36 (1.00, 1.86)-fold higher odds of reaching a Kellgren-Lawrence score of 3 or 4 within a year.

Conclusions

High FRAX predicts thinner cartilage and weaker subchondral bone within a year. Complementing standard OA clinical risk factors with FRAX calculation could help identify individuals likely to develop worse knee OA radiologic outcomes.