LONGITUDINAL CHANGES IN PERI-ARTICULAR BMD USING QUANTITATIVE CT IN KNEE OA PATIENTS: DATA FROM THE IMI-APPROACH...

Increasing evidence suggests that peri-articular bone remodeling plays a key role in the development and progression of osteoarthritis (OA). However, a critical knowledge gap remains regarding depth-specific longitudinal changes in peri-articular bone mineral density (BMD) in both the periarticular femur and tibia.

Describe depth-specific longitudinal changes over two years in peri-articular BMD in the femoral and tibial epiphysis using quantitative CT (QCT) among patients with pre-radiographic versus established radiographic OA.

The IMI-APPROACH study is a multicenter cohort including patients with clinical and/or structural knee OA. The present analysis included participants who had QCT and radiographic examinations at baseline and 2-year follow-up. QCT was used to assess BMD change at the medial and lateral femur and tibia at 4 volumes of interest with increasing distance from the hyaline cartilage: 1. Cortical bone plate (Cort), 2. Subchondral area (Sub), 3. Mid-epiphysis (Mid), and 4. Adjacent to the physis (Juxta). Baseline radiographs were used to determine the Kellgren and Lawrence grade (KLG) and to categorize patients into pre-radiographic OA (KLG 0-1) and radiographic OA (KLG ≥2). We used linear mixed-effects models (LMMs) to evaluate the anatomical gradient in mean percentage change in BMD from the joint surface to the deep bone. Mean percentage change in BMD was modeled as the continuous dependent variable, with depth rank from cortical to juxta-articular bone included as a fixed effect. A random intercept for patient ID was included to account for repeated measures within patients. To determine if the depth-dependent trajectory of BMD loss differed significantly between pre-radiographic and radiographic OA, an interaction term (depth rank*OA status) was included in the models. Additionally, we reported BMD change as a categorical variable (gain ≥5% increase in BMD over the study time, loss≥5% decrease in BMD, stable= within 5% of baseline BMD) in each region of interest of the tibial plateaus.

177 knees from 177 participants were included. The mean age was 67 years (SD = 7), 76% of participants were female, and the mean BMI was 27.98 kg/m² (SD = 4.9). Both medial and lateral femoral condyles and tibial plateaus showed progressively greater BMD loss over 24 months from the cortical bone plate to the juxta-physeal region. When BMD change was treated as a continuous variable, the anatomical gradient of BMD loss across tissue depths in the femoral condyles was significantly steeper in patients with established radiographic OA compared to those with pre-radiographic OA (Figure 1). This depth-dependent trajectory was particularly pronounced in the medial condyle (interaction p < 0.001) and was also significant in the lateral condyle (interaction p = 0.016). Conversely, the tibial plateaus showed no substantial difference in trajectory between radiographic OA and pre-radiographic OA patients (p = 0.979 for the medial compartment; p = 0.260 for the lateral compartment). When BMD change was used as a categorical variable (loss, stable, gain), up to 27.9% and up to 22.3% participants showed substantial BMD gains in the subchondral regions of the medial and lateral tibial plateaus, respectively (Figure 2).

Periarticular BMD change around the knee is common among patients with knee OA. There are bone- and depth-specific changes in periarticular BMD that are influenced by radiographic status. Future studies investigating the association of CT based BMD changes with knee OA-related pain and functional impairments may help determine the clinical significance of these QCT based findings.