REVEALING EARLY SUBCHONDRAL BONE STRUCTURAL CHANGES IN OSTEOARTHRITIS PROGRESSION IN A COLLAGENASE-INDUCED MOUSE MODEL USING MICRO COMPUTED TOMOGRAPHY

INTRODUCTION

The deployment of micro-computed tomography (microCT) enables quantitative morphometric analysis (QMA) to quantify morphological and structural changes caused by OA in mouse knee joint with excellent spatial resolution. Previous studies quantifying microstructural changes to subchondral tibiae in fortnightly intervals, report bone loss and trabecular thinning as early as two weeks post disease induction in mouse models. However, evidence suggests that the subchondral bone turnover may occur earlier than two weeks post disease induction in a mouse OA model.

OBJECTIVE

To reveal early bone microstructural changes associated with OA progression in a mouse model with a high temporal resolution using microCT and QMA.

METHODS

Seventy-five male C57BL/10 mice aged nine weeks were recruited and randomly assigned to three cross-sectional cohorts, i.e., baseline (n = 4), control (n = 24) and OA (n = 47) cohorts. Forty-seven ten-week-old mice assigned to OA cohort received intra-articular injection of 10 unit of filtered collagenase dissolved in 6 µl physiological saline to the right joints (OA group) through the patellar ligament. A similar volume of saline was intraarticularly injected to the left contralateral joints (CTLR group). Prior to scanning, mice were euthanized at 0-, 1-, 2-, 3-, 4-, 5-, 6-, 7-, and 8-weeks post ten-week-old. Scans were performed using microCT (vivaCT80, SCANCO Medical AG, Brüttisellen, Switzerland) with a source voltage of 70 kVp, an integration time of 350 ms, a current of 114 µA, a nominal resolution of 10.4 µm, and 500 projections with each scan taking around 20 minutes. QMA was performed to quantify changes to subchondral bone microstructure associated with OA progression. To detect differences between treatments at each time point, a linear mixed-effect model was used. Individual mice were considered as random effects, time points (1- to 8- weeks post collagenase injection) and treatment (CT, CTLR, and OA) were considered as fixed effects.

RESULTS

Representative segmented microCT images from CT and OA group can be found in Figure 1 A. Typical osteoarthritic characteristics were observed in OA group at multiple time points, with changes detectable as early as one week post disease induction, shown in Figure 1 B. Specifically, comparing joints from CT and CTLR groups, smaller trabecular thickness, Tb.Th, were observed at both lateral and medial sides in OA femora, in accordance with the increasing trabecular spacing, Tb.Sp, and decreasing trabecular number, Tb.N.

CONCLUSION

This study, for the first time, demonstrated that prominent bone changes could be detected as early as one week after disease induction. These findings underscore the necessity of early quantification to capture rapidly changing bone microstructure alterations in early stage OA, potentially enabling earlier diagnosis, intervention, and treatment.