The Plantar Aponeurosis in Fetuses and Adults: An Aponeurosis or Fascia?

Abstract

SUMMARY:The plantar aponeurosis (PA), which is a thickened layer of deep fascia located on the plantar surface of the foot, is comprised of three parts. There are differing opinions on its nomenclature since various authors use the terms PA and plantar fascia (PF) interchangeably. In addition, the variable classifications of its parts has led to confusion. In order to assess the nature of the PA, this study documented its morphology. Furthermore, a pilot histological analysis was conducted to examine whether the structure is an aponeurosis or fascia. This study comprised of a morphological analysis of the three parts of the PA by micro-and macro-dissection of 50 fetal and 50 adult cadaveric feet, respectively (total n=100). Furthermore, a pilot histological analysis was conducted on five fetuses (n=10) and five adults (n=10) (total n=20). In each foot, the histological analysis was conducted on the three parts of the plantar aponeurosis, i.e. the central, lateral, and medial at their calcaneal origin (total n=60). Fetuses: i) Morphology: In 66 % (33/50) of the specimens, the standard anatomical pattern was observed, viz. three parts (i.e. central, lateral, medial) that originated from the medial and lateral processes of the calcaneal tuberosity and inserted onto the metatarsals. In 18 % (9/50) of the specimens, a two-part structure was observed. Variable origins of the medial part were noted in 16 % (8/50) of the specimens. In order to document these variations, the central part of the PA was divided into three segments (i.e. upper, middle, lower): a) In 63 % (5/8) of the specimens, the medial part arose from the middle segment; b) In 37 % (3/8) of the specimens, the medial part arose from the middle and upper segments. ii) Histological analysis: a) The central part contained longitudinally arranged semi-dense type I collagen fibres with fibroblasts; b) The lateral part displayed semi-dense type I collagen fibres with fibroblasts, hyaluronic acid, corpusculum sensorium fusiforme (Ruffini corpuscle) and corpusculum lamellosum (Pacinian corpuscle); c) The medial part comprised of loose connective tissue with elastic and reticular fibres. Adults: i) Morphology: In 100 % of the specimens, the standard anatomical pattern was observed. ii) Histological Analysis: a) In the central part, longitudinally arranged type I collagen fibres with fibroblasts were visible; b) The lateral part contained longitudinally arranged type I collagen fibres with fibroblasts; c) The medial part comprised of loose connective tissue, type I and type III collagen fibres, elastic and reticular fibres. In the current study, the morphology of the PA in fetuses and adults conformed to the standard anatomical description with variations in the origin of the medial part observed in fetuses. In addition, the fetal specimens displayed a two-part structure of the PA when the medial part was absent. Microscopically, the findings suggest that only the central and lateral parts may be considered as the PA, whilst the medial part may be termed the PF.