REGIONAL VARIATION IN TRAPEZIOMETACARPAL BONE MICROARCHITECTURE IN FEMALES WITH OSTEOARTHRITIS USING HR-PQCT

INTRODUCTION

The trapeziometacarpal (TMC) joint, comprised of the trapezium (TRP) and first metacarpal (MC1) bones, is a mechanically complex, saddle-shaped joint. Studies have estimated that the peak forces acting on the TMC joint are up to five times higher than the corresponding external forces [1]. Moreover, cadaveric studies have shown non-uniform cartilage loss in TMC joint with OA [2]. While several cadaveric studies have investigated TMC joint cartilage and bone changes, evaluation of subchondral bone changes in the TMC joint in vivo is lacking.

OBJECTIVE

The objective of this study was to investigate differences in bone microarchitecture in anatomical quadrants of the TMC joint in women with TMC OA compared to age- and sex-matched controls. We hypothesized that women with TMC OA will exhibit quadrant-specific differences in bone microarchitecture compared to controls. Specifically, we hypothesized that the volar region of the TMC joint will demonstrate an increase in trabecular thickness, bone volume, and volumetric bone mineral density due to localized bone adaptations as a response to increased loading in the volar region.

METHODS

14 females diagnosed with symptomatic TMC OA (mean age: 60 ± 6.5 years) and 12 similarly aged female controls (mean age: 59 ± 5.7 years) were scanned using HR-pQCT (XtremeCT2, Scanco Medical). A standard HR-pQCT scanning protocol was used (61 µm³ voxels). Images were preprocessed using a Laplace-Hamming filter and segmented with a fixed threshold (15% of the maximum intensity). A bone coordinate system was automatically defined for the MC1 and TRP [3], and used to separate each bone into four anatomical quadrants: 1) radial-dorsal (RD), 2) radial-volar (RV), 3) ulnar-dorsal (UD), and 4) ulnar-volar (UV). For each whole bone and quadrant, we computed volumetric bone mineral density (vBMD, mg HA/cm³), bone volume fraction (BV/TV, %), and bone thickness (B.Th, mm). A mixed ANOVA was used to compare bone measures in each bone and quadrant between groups.

RESULTS

We did not observe a significant difference in total bone parameters between groups for the MC1 or TRP. However, we found a statistically significant interaction effect between the volar and dorsal quadrants of the TRP and group for B.Th (p = 0.02, Figure 1, Table 1). Compared to controls, the mean B.Th in the TRP of the OA group was 1.9% lower in the RD quadrant, 7.5% lower in the UD quadrant, 4.8% greater in the RV quadrant, and 6.2% greater in the UV quadrant.

CONCLUSION

Our results suggest that whole bone TMC microarchitecture may not differ between OA and controls; however, we found significant differences in quadrant bone microarchitecture. This suggests that the MC1 and TRP undergo localized bone microarchitectural changes to adapt to the loading of the TMC joint. Further, our results suggest that bone thickness in the volar region of the trapezium may increase with TMC OA. The TMC joint ligaments aid in distributing forces in the joint, which can be affected in TMC OA. Koff et al. found thinner cartilage in the volar region of the TMC joint in OA, which may be attributed to increased loads [2]. In this study, bones were not further subdivided into trabecular and cortical regions as the trapezium does not have a clear separation between these regions. Combined with the small sample size, this may explain the lack of significance in vBMD and BV/TV between groups. Subchondral sclerotic bone was 50% thicker in cadaveric trapezia with OA [4]. Thus, developing an algorithm to reliably separate these regions in the trapezium may provide further insights into regional effects of TMC OA on cortical and trabecular bone.