Tibial cancellous bone changes in patients with knee osteoarthritis. A short-term longitudinal study using Fractal Signature Analysis.

Objective: To quantify tibial cancellous bone changes over 24 months in patients with medial compartment knee osteoarthritis (OA) subdivided into those with slow or detectable joint space narrowing (JSN).

Method: Digitised macroradiographs (4x) were obtained at baseline and 24 months from 40 patients (F:26) and subdivided by computerised measurement of minimum medial compartment joint space width (JSW) into those with slow JSN (<0.2 mm/year, n=66) or detectable JSN (>or=0.2 mm/year, n=14) and who had a mean (range) JSW at baseline of 3.89 (1.66-5.48) mm and 3.73 (2.49-5.74) mm, respectively. Fractal Signature Analysis measured longitudinal change in bone structure at four regions of interest (ROI): medial and lateral subchondral (Sc) and subarticular (Sa) regions.

Results: Mean (range) JSN for slow and detectable groups was 0.01 (-0.31-0.18) mm/year and 0.44 (0.20-1.01)mm/year, respectively. All ROIs in both groups had significant (P<0.05) decrease in fractal dimension (FD) at most trabecular sizes (vertical: 0.36-1.14 mm; horizontal: 0.36-1.14 mm, excluding the lateral Sa region) over 24 months. There were no between-group differences except at a few trabecular sizes within the Sa regions where the detectable JSN group had significantly (P<0.05) greater decrease in FD compared to the slow JSN group (medial: horizontal sizes 0.54-0.72 mm, 1.02-1.08 mm; lateral: vertical sizes 0.90-1.02 mm).

Conclusion: Bone loss occurred in all knees with medial compartment OA. Decrease in FD of vertical and horizontal trabeculae was consistent with decrease in trabecular number associated with loss. The pattern of bone loss was similar in knees with slow and detectable JSN.