Subchondral bone trabecular integrity predicts and changes concurrently with radiographic and magnetic resonance imaging-determined knee osteoarthritis progression

Abstract

Objective: To evaluate subchondral bone trabecular integrity (BTI) on radiographs as a predictor of knee osteoarthritis (OA) progression.

Methods: Longitudinal (baseline, 12-month, and 24-month) knee radiographs were available for 60 female subjects with knee OA. OA progression was defined by 12- and 24-month changes in radiographic medial compartment minimal joint space width (JSW) and medial joint space area (JSA), and by medial tibial and femoral cartilage volume on magnetic resonance imaging. BTI of the medial tibial plateau was analyzed by fractal signature analysis using commercially available software. Receiver operating characteristic (ROC) curves for BTI were used to predict a 5% change in OA progression parameters.

Results: Individual terms (linear and quadratic) of baseline BTI of vertical trabeculae predicted knee OA progression based on 12- and 24-month changes in JSA (P < 0.01 for 24 months), 24-month change in tibial (P < 0.05), but not femoral, cartilage volume, and 24-month change in JSW (P = 0.05). ROC curves using both terms of baseline BTI predicted a 5% change in the following OA progression parameters over 24 months with high accuracy, as reflected by the area under the curve measures: JSW 81%, JSA 85%, tibial cartilage volume 75%, and femoral cartilage volume 85%. Change in BTI was also significantly associated (P < 0.05) with concurrent change in JSA over 12 and 24 months and with change in tibial cartilage volume over 24 months.

Conclusion: BTI predicts structural OA progression as determined by radiographic and MRI outcomes. BTI may therefore be worthy of study as an outcome measure for OA studies and clinical trials.

Figure 1. Landmarks used to quantify joint space area

The inner and outer joint space area boundaries were defined by the position of the inner and outer margins of the tibial fossa landmark respectively, as determined by the model-fitting process of the KneeAnalyzer tool. These two points (indicated by black asterisks) were defined as follows: the inner margin of the tibial fossa was the point where the lower margin of the tibial fossa (bowl) converges with the projected edge of the tibial plateau, on the side nearest to the inner edge of the knee (point 35 in the annotated image); the outer margin of the tibial fossa: the point where the lower margin of the tibial fossa converges with the projected edge of the tibial plateau, on the side nearest to the outer edge of the knee (point 36 in the annotated image). These two points are located implicitly by the model-based segmentation algorithm for finding the whole tibial plateau.

Figure 2. Receiver Operating Characteristic (ROC) curve of bone trabecular integrity (BTI) for predicting osteoarthritis progression over 24 months

ROC curve analysis was performed to evaluate the capability of medial compartment subchondral tibial BTI to predict a 5% change over 24 months in: A) medial joint space area (JSA); B) medial minimum joint space width (JSW); C) medial tibial cartilage volume (VC_MT); and D) medial femoral cartilage volume (VC_MF). Curves depict the AUC (red line), plus (blue line) and minus (green line) one standard deviation (SD) derived after conservative iterative cross-validation.