Mandibular Condyle Shape Changes Following Unilateral Partial Discectomy in Mice

Hypothesis and Objective: Osteoarthritis (OA) of the temporomandibular joint manifests as bony remodeling, sclerosis, and cartilage degeneration, leading to joint immobility and pain. The most promising diagnostic marker for TMJ OA is morphological changes in the mandibular condyle, e.g., condylar flattening, osteophytic lipping, and bony erosion. In mice, performing unilateral partial discectomy induces TMJ osteoarthritic changes which provides a model to better understand the processes leading to the progression of TMJ OA. The objective of this study is to determine if the bony remodeling that occurs during OA progression changes the shape of the mandibular condyle. Methods: Unilateral partial discectomies were performed on skeletally mature male and female c57 BL6/J mice. Four-weeks after OA induction, the heads were fixed overnight in 4% paraformaldehyde, μCT scanned. The condyles were segmented and landmarked. Landmark coordinates were superimposed using a Procrustes alignment and shape characterized using a principal components analysis (PCA). Results: The PCA yielded 27 PCs, with the first five chosen for further analysis based on accounting for >5% of the entire variation. Only PC1 showed a statistically significantly different difference in shape (p<0.001) between non-surgical controls and the osteoarthritis group. With higher PC1 scores, the osteoarthritis group had condylar heads that were much wider in the mediolateral dimension and flatter in the superoinferior dimension. The difference was so striking that there was no overlap between the scores of the two groups. There were no significant differences found for sex. Conclusions: Contrary to expectations, there were no sex differences in the shape of the condyle in the osteoarthritis group. These results support prior work, and emphasize how rapidly dramatic remodeling affects not only the subchondral architecture but also the shape of the condyle. Funding: 1R01DE029835-01 and the OMS Foundation Research Support Grant IRB and/or ACC Protocol #: ACC #20-068