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The statistical analysis of morphometric data collected from biopsies of human superficial peroneal nerve is complicated by the heterogeneity of the population of myelinated fibres. In order to make separate statistical analyses of the subpopulations of large and small fibres we have developed a computer program (written in PASCAL) for their automatic separation. The method is based on a dynamic centres clustering algorithm and was applied to the multifactorial space defined by the principal component analysis of the morphometric variables: axonal diameter, myelin sheath thickness, circularity index and g-ratio. The classification technique was applied to measurements obtained from 5 control nerves, and to simulated data, and in each case it gave consistent Gaussian subpopulations with no need for the introduction of supplementary variables.

Morphometric studies of peripheral nerves (PN) usually involve some sampling of the myelinated fibres (MF). In order to scrutinize the statistical properties of the sampling processes in common use and the reliability of the resulting estimates, a quantitative analysis of human superficial peroneal nerves from 8 different normal subjects was undertaken at the ultrastructural level, both in terms of MF spatial distribution and of their size distribution. This study used sampling rates involving more than 10% of the whole myelinated fibre population observed in each nerve fascicle. However, in nearly all the fascicles evaluated, the sampling fluctuations are so high that neither the number of axons nor their diameter distribution can be assessed with enough accuracy. A systematic study of the myelinated fibres shows that the spatial distribution of their size is not uniform. This marked heterogeneity in the MF size distribution imposes measurement of large enough samples (500 or 600 MFs usually represent about one-half or two-thirds of the whole MF population) in a way to secure a reliable enough estimate of the density and size distributions. However, the practical usefulness of sampling schemes requiring more than one-half of the whole MF population in a nerve fascicle, is questionable.