Three-dimensional morphology of heel fat pad: an in vivo computed tomography study

Abstract

Heel fat pad cushioning efficiency is the result of its structure, shape and thickness. However, while a number of studies have investigated heel fat pad (HFP) anatomy, structural behavior and material properties, no previous study has described its three-dimensional morphology in situ. The assessment of the healthy, unloaded, three-dimensional morphology of heel pad may contribute to deepen the understanding of its role and behavior during locomotion. It is the basis for the assessment of possible HFP morphological modifications due to changes in the amount or distribution of the loads normally sustained by the foot. It may also help in guiding the surgical reconstruction of the pad and in improving footwear design, as well as in developing a correct heel pad geometry for finite element models of the foot. Therefore the purpose of this study was to obtain a complete analysis of HFP three-dimensional morphology in situ. The right foot of nine healthy volunteers was scanned with computed tomography. A methodological approach that maximizes reliability and repeatability of the data was developed by building a device to lock the foot in a neutral position with respect to the scan planes during image acquisition. Scan data were used to reconstruct virtual three-dimensional models for both the calcaneus and HFP. A set of virtual coronal and axial sections were extracted from the three-dimensional model of each HFP and processed to extract a set of one- and two-dimensional morphometrical measurements for a detailed description of heel pad morphology. The tissue exhibited a consistent and sophisticated morphology that may reflect the biomechanics of the foot support. HFP was found to be have a crest on its anterior dorsal surface, flanges on the sides and posteriorly, and a thick portion that reached and covered the posterior surface of the calcaneus and the achilles tendon insertion. Its anterior internal portion was thinner and a lump of fat was consistently present in this region. Finally, HFP was found to be thicker in males than in females.

© 2011 The Authors. Journal of Anatomy © 2011 Anatomical Society of Great Britain and Ireland.

Figures

Fig. 1

CT scan of the foot with the positioning device. The device consist of a leg board (LB) and a foot board (FB). The black line drawn on the FB is the reference line for alignment of foot longitudinal axis (FLA). The white lines represent the scan lines.

Fig. 2

HFP segmentation. (A,B) HFP segmentation (inside the black line) on sagittal slices. As a clear line separating the HFP and hypodermis could not be clearly defined, segmentation of the HFP side walls is uncertain (A). In contrast, the segmentation of the HFP beneath the calcaneus was easily performed (B). (C,D) Unstructured (arrow) fat of the heel. The unstructured fat is located in the antero-medial side of the rear foot. (C) Coronal view. (D) Axial view.

Fig. 3

Generation of HFP sections. (A,B) Generation of coronal sections. (A) Identification of coronal planes. The step increment of 13% of calcaneus length was chosen to detect the plantar tuberosity of the calcaneus (i.e. the point where HFP thickness was measured in previous studies). (B) Extrapolation of HFP coronal sections. The coronal sections were numbered one to 10 starting from the most posterior section forward. (C,D) Generation of axial sections. (C) Identification of the axial planes. The step increment of 18% was chosen to detect the most posterior point of the calcaneus. (D) Extrapolation of HFP axial sections. To isolate the tissue behind the calcaneus, the posterior HFP was sectioned with the axial planes. The axial sections were numbered one to four starting from the most proximal section.

Fig. 4

HFPs of the nine subjects of the study.

Fig. 5

Comparison of coronal section thicknesses between males and females. (A) Average coronal section thickness (ACST, mean values) for males and females. (B) Maximum coronal section thickness (MCST, mean values) for males and females.

Fig. 6

HFP qualitative data. (A) Localization of the points defining maximum and minimum coronal section thicknesses (MCST and MiCST). (B) Representation of the crest approximating line (CAL) with respect to the foot longitudinal axis (FLA). (C) Representation of the points defining the crest maximal thickness (CMT) with respect to the points of the crest peaks. (D) Measurement of the HFP thickness on the internal and external sides.

Fig. 7

HFP axial section data. (A) Localization of the points of maximum axial section thickness (MAST). (B) Comparison of the average axial section thickness (AAST) in males and females.

Fig. 8

Findings of the study. (A) Representation of the HFP morphological peculiarities. (B) Spatial relationship between the retrocalcaneal HFP and the achilles tendon insertion. (C) HFP crest is located between the flexor digitorum brevis and the abductor digiti minimi. (D) The unstructured fat area is located on the antero-medial side of the heel, close to the foot arch. (E) HFP thickness is more homogeneously distributed on the posterior rather than on the anterior side. (F) Only slight foot plantarflexion was necessary to leave the heel unloaded during the CT scan.