To quantify differences in bone structure in the proximal tibia of patients with mild, definite and advanced osteoarthritis (OA) compared to healthy reference tibiae.
Patients with medial compartment OA (n=110; F=70), mean+/-SD age 61.0+/-10.2 years, and non-OA reference subjects (n = 27; F = 10) mean+/-SD age 36.3+/-11.4 years had 4x macroradiographs digitised by laser scanner. Computer measurement of minimum medial joint space width (JSW) subdivided available OA knees into those with early (JSW > 3 mm, n=70), definite (JSW </= 3 > 1.5 mm, n = 52) and advanced OA (JSW </= 1.5 mm, n = 60). Non-OA knees (n = 49) had JSW > 4.5 mm. Fractal Signature Analysis (FSA), a computerised image analysis technique, measured differences in cancellous bone structure between OA and non-OA tibiae at four regions of interest (ROIs).
Compared to non-OA, FSA of vertical trabeculae increased significantly (P < 0.05) at most sizes (0.12-1.14 mm) in all OA subgroups and ROIs, with greatest increase occurring in the medial diseased compartment. Compared to early OA, FSA of vertical trabeculae increased significantly (P<0.05) at most sizes (0.36-1.14 mm) in subchondral and subarticular ROIs in definite and advanced OA. Compared to non-OA, FSA of horizontal trabeculae increased significantly (P < 0.05) at some small sizes in all ROIs and OA subgroups, and decreased significantly (P<0.05) at large sized horizontal trabeculae (0.60-1.14 mm) in the medial subarticular region in advanced OA.
The increase in FSA (consistent with increased trabecular number associated with thinning and fenestration in regions of dense cancellous bone) of most vertical and some horizontal trabeculae confirms that cancellous bone within the proximal tibia of OA patients is osteoporotic.