Pain is the predominant symptom of OA, a debilitating disease marked by changes in cartilage and subchondral bone, but pain pathophysiology is poorly understood. Bone is densely innervated and may be linked to OA-related knee pain. Quantitative computed tomography (QCT) is an in vivo image-based technique with the potential to quantify bone mineral density (BMD) to explore the role of bone in OA-related pain. When coupled with subject-specific finite element (FE) modeling, it may be possible to clarify the mechanical role of bone in OA-related knee pain.
The objectives of this study were to assess if: 1) tibial subchondral BMD is associated with OA-related nocturnal knee pain using depth-specific QCT image processing, 2) tibial epiphyseal and metaphyseal BMD is associated with OA-related knee pain using a modified depth-specific CT image processing tool, 3) subchondral cyst characteristics are associated with OA-related knee pain, and 4) FE-derived mechanical outcomes at the proximal tibia are associated with OA-related pain.
Lateral focal subchondral BMD was 33% higher in participants with severe nocturnal pain than participants with no nocturnal pain at the 2.5-5mm depth (p=0.028) and 32% higher at 5-10mm from the subchondral surface (p=0.049). At the epiphyseal and metaphyseal depths, higher total pain was associated with lower medial epiphyseal BMD (R² =-0.40, p=0.002), and lower metaphyseal BMD (R² =-0.35, p=0.017). At the lateral region, subchondral cyst number (r=0.55, p<0.001) and cyst number per proximal tibial volume (r=0.52, p<0.001) were both associated with BMD, and lateral cyst number and volume were associated with joint space narrowing (r=0.52 to 0.68, p<0.001) and alignment (r=0.44 to 0.62, p<0.001). In our FE study, principal compressive stress was associated with nocturnal pain at most lateral regions (r=0.33 to 0.50, p<0.05). Principal compressive stress at the lateral region ranged from 47% to 67% higher (p<0.05) in participants with severe nocturnal pain than participants with no pain.
This series of studies suggests that pain in patients with knee OA may be associated with BMD throughout various depths at the proximal tibia as well as FE-based bone mechanical outcomes, such as principal compressive stress. These findings suggest previously unexplored associations between OA-related knee pain and BMD or mechanical outcomes, emphasizing that bone may have a mechanical role in OA-related pain pathogenesis.