Osteoporosis in Those with Knee Osteoarthritis - Differences in Disease Profile and Correlates of Knee Pain: The Osteoarthritis Initiative

Objectives: to explore the hypothesis that knee osteoarthritis patients with osteoporosis represent a sub-cohort with different disease characteristics and origin of symptoms. Methods: Men and women in the Osteoarthritis Initiative (OAI) at visit 5 (36 months) were examined for osteoporosis (N=1483) using DXA (T-score at femoral neck ≤-2.5), use of bisphosphonates within the last 5 years, or having experienced a fracture within the last 36 months. Those with and without osteoporosis were compared in terms of subchondral bone quality, bone marrow lesion (BML) size, number and effusion, as well as cartilage thickness, all measured using MRI, with general linear modeling. Moderation analysis examined the relationship between symptoms (measured 12 months later) and each of cartilage or subchondral bone image features conditional on the presence of osteoporosis. Results: 15.2% of 1246 participants (825 women, 658 men, mean age: 64.4±8.9yrs, BMI: 30.1±4.9 kg/m2) likely had a higher risk osteoporosis status and showed lower medial and lateral subchondral bone density, smaller trabecular number, and larger trabecular separation (all p<0.01) compared to those without. Cartilage thickness appeared lower in this group (p=0.04) but only by a small amount. Both BML properties and cartilage thickness correlated with knee symptoms in the full cohort. Osteoporosis was a significant moderator for knee symptoms’ relationship with cartilage thickness but not for BML properties. Specifically, those with osteoporosis showed no relationship between cartilage thickness and any measure of knee symptoms, but they did demonstrate bone-related influence on symptoms. Conclusions: Those with osteoporosis exhibit different subchondral bone and cartilage properties. The origin of symptoms in this subgroup is largely focused on the bone and not cartilage, which differs from those with knee osteoarthritis but without osteoporosis. Osteoporosis likely has a significant impact not only on typical hip and spine central sites, but also at major joints like the knee.