Evaluation of Obturator Nerve Fascicular Topography Using Landmark Morphometrics ‐ a Pilot Study
Authors: Izadpanah Hasti , Millard Jonathan A. , Roballo Kelly 
Published: May 2022

Introduction

While the overall macroanatomy of peripheral nerves in the lower extremities are well researched, the intricacy of fascicular organization within larger polyfascicular nerves render them difficult to characterize. This obstacle is particularly salient considering the serviceability of these complex nerves in gross motor functions. Peripheral nerve injuries (PNI) occur in approximately 1.64% of people who have had trauma involving the upper or lower limb. Rates of effective distal reanimation using autologous nerve grafts remain low. The objective of this pilot research is to demonstrate the utility of landmark morphometric techniques in gaining a more comprehensive understanding of fascicular topography, leading to improved precision in clinical interventions.

Material and methods

Right and left obturator nerves from the 25 formalin‐fixed whole‐body donors were isolated using typical dissection techniques. Sections of the nerves were collected from their immediate origin from the lumbar plexus to their exit from the obturator canal. Nerves were sectioned into nine equally divided segments and imaged (OptixCam Summit K2). Images of the nerve sections were evaluated for fascicle number and diameter (ImageJ). Nerves were then categorized by fascicular homology. Samples with matching fascicle numbers and arrangements were used for further analysis. Nine individuals were selected for landmark morphometric analyses and 130 landmarks were collected via semi‐landmark techniques (tpsdig232 v. 2w32). Generalized Procrustes analysis was performed to determine the mean landmark configuration, and a principal component analysis was used to explore variability in fascicular topography MorphoJ (v.1.07a). Wireframe graphs, lollipop diagrams, and transformation grids were generated to evaluate and visualize findings.

Results

The average obturator nerve diameter of the original 25 donors was 2.29 cm (right) and 2.28 cm (left). Nerve length was 10.86 cm (right) and 10.83 cm (left). Principal component analysis revealed eight principal components, with the first two principal components explaining 64.6% of the overall shape variation. Both PC1 and PC2 show peripheral fascicles remaining more consistently located, while the direction and magnitude of variability demonstrated by the lollipop diagrams suggest much more variation in the relative locations of more interior fascicles.

Conclusions and significance

This pilot study successfully utilized a novel approach of examining the variability of peripheral nerve fascicles using landmark morphometric techniques. Peripheral fascicles of the intra‐abdominal obturator nerve were relatively consistent, while more interior fascicular bundles showed marked variability in their locations. Consequently, the relative location of non‐fascicular tissue was most variable in the central regions of the nerve. The application of these techniques in larger samples may inform grafting approaches which aim to provide adequate alignment and guidance of extraneural tissues supporting effective axon growth.