Fractal Analysis of Trabecular Bone in Knee Osteoarthritis (OA) is a More Sensitive Marker of Disease Status than Bone Mineral Density (BMD)

The purpose of this study was to determine whether fractal analysis (FSA) of macroradiographs or bone mineral density (BMD) is more sensitive in detecting disease-related cancellous bone alterations in knee osteoarthritis (OA). Differences in BMD between 11 OA (6 females) and 11 non-OA reference (7 females) tibiae were compared with differences in trabecular organization measured by computerized method of fractal signature analysis (FSA) of digitized macroradiographs (×3.5 to ×5). OA knees had anatomic and radiographic evidence of medial compartment disease. FSA measured cancellous bone organization at 4 regions of interest (ROI): medial and lateral subchondral (Sc) and subarticular (Sa) sites, dual X-ray absorptiometry (DXA) measured BMD at the same ROIs. Compared to non-OA, OA tibiae had significant increased (P < 0.05) in FSA of vertical trabeculae in the medial Sa region (trabecular size range: 0.42–0.54; 0.90–1.98 mm) and significant decrease (P < 0.05) in FSA for some horizontal trabeculae in the Sc region (trabecular size range: medial side 0.12–0.18 mm; lateral side 0.12–0.24 mm). Compared to non-OA, BMD of OA tibiae was not significantly different at any ROI. BMD was not sensitive to changes in trabecular organization detected by FSA. The increase in FSA of vertical trabeculae in the medial Sa region was consistent with trabecular fenestration and thinning, which may have been detected as decreased BMD in a larger sample. For studies involving small sample sizes, quantifying changes in trabecular organization is more sensitive than BMD for detecting bone alterations in knee OA.