Statistical shape analysis of the incus.

Area of Science:

• Anatomy
• Biomedical Engineering
• Otolaryngology

Background:

• The incus, a key auditory ossicle, is frequently involved in oculoplastic procedures with high failure rates.
• Current understanding of incus morphology is limited to linear dimensions, hindering detailed analysis.
• A landmark-based approach is needed to comprehensively capture and quantify incus bone shape.

Purpose of the Study:

• To develop and apply a novel landmark-based geometric morphometric method for incus shape quantification.
• To analyze the morphological variation of the incus bone in a human donor sample.
• To investigate potential correlations between incus size, shape, and anatomical variations.

Main Methods:

• Harvesting and micro-computed tomography (micro-CT) scanning of 53 human incus bones.
• Utilizing 3DSlicer for landmarking and principal component analysis (PCA) to identify major shape variations.
• Comparing shape variations between sexes and sides using Wilcoxon rank-sum tests and correlating centroid size with shape scores.

Main Results:

• Principal component analysis identified key axes of variation, with the first ten PCs explaining 83.5% of the shape differences.
• The primary variation (PC1) related to inverse crural lengths, and PC2 to incudomallear joint angulation.
• No significant shape differences were found between sexes or sides; centroid size correlated significantly with PC1 scores.

Conclusions:

• Incus crural morphology, specifically lengthening and anterior curvature, may indicate adaptations to increased bone size.
• Significant variation in the incudomallear joint angle is a notable finding.
• Understanding incus shape variations is crucial for evaluating predisposition to pathological processes and improving surgical outcomes.