732 - Using 3D Shape Analysis to Assess Patellar Morphological Variability – Considerations for Patellar Instability

Objectives: Patellar morphology has been shown to aid in the diagnosis and prognosis of patellofemoral disorders. There is limited data on 3D geometric analysis of patellar morphology. Geometric morphometric analysis allows for anatomic retention of original structures through direct study of landmarks and provides powerful visual information which can be used to study shape differences. The primary aim of this research is to improve current understanding of patellar shape variation by using these techniques. A secondary aim is to evaluate how patellar shape varies with patellar size.

Design: Typical dissection techniques were performed to remove left sided patella from 20 formalin-fixed cadavers. Images of dissected patellae were scanned in a Bruker Skyscan 1276 µCT at 50µm resolution. Scans were imported into 3DSlicer (v.5.6.2) for segmentation. The Markups module was used to apply 98 homologous landmarks onto the surfaces of the patellae. The Slicermorph module was used to apply a generalized Procrustes analysis and principal component analysis (PCA).

Results: The PCA resulted in 20 principal components (PC) with the first five PCs accounting for 73.85% of the variation in the sample. PC1 represents 26.66 % of the variation and is characterized by changes in the shape of the apex, while PC2 (17.85%) showed changes in the medial facet. A weak to moderate correlation (r = .24) was found between centroid size and PC1. A moderate to strong correlation was found (r =.72) when five outliers were dropped.

Conclusions: Our results show the apex is the primary driver of shape variation, followed by the medial articular facet in left sided patella. This is significant, as both the apex and medial facet have been shown to have morphological significance in the pathophysiology of patellofemoral instability. Additionally, change in the variation of the patellar apex had a correlation with patellar size, while other anatomical landmarks did not.