Subcutaneous fascial bands--a qualitative and morphometric analysis

Abstract

Background: Although fascial bands within the subcutaneous (SQ) layer are commonly seen in ultrasound images, little is known about their functional role, much less their structural characteristics. This study's objective is to describe the morphological features of SQ fascial bands and to systematically evaluate the bands using image analyses tools and morphometric measures.

Methods: In 28 healthy volunteers, ultrasound images were obtained at three body locations: the lateral aspect of the upper arm, medial aspect of the thigh and posterior aspect of lower leg. Using image analytical techniques, the total SQ band area, fascial band number, fascial band thickness, and SQ zone (layer) thickness were determined. In addition, the SQ spatial coherence was calculated based on the eigenvalues associated with the largest and smallest eigenvectors of the images.

Results: Fascial bands at these sites were contiguous with the dermis and the epimysium forming an interconnected network within the subcutaneous tissue. Subcutaneous blood vessels were also frequently encased by these fascial bands. The total SQ fascial band area was greater at the thigh and calf compared to the arm and was unrelated to SQ layer (zone) thickness. The thigh was associated with highest average number of fascial bands while calf was associated with the greatest average fascial band thickness. Across body regions, greater SQ zone thickness was associated with thinner fascial bands. SQ coherence was significantly associated with SQ zone thickness and body location (calf with statistically greater coherence compared to arm).

Conclusion: Fascial bands are structural bridges that mechanically link the skin, subcutaneous layer, and deeper muscle layers. This cohesive network also encases subcutaneous vessels and may indirectly mediate blood flow. The quantity and morphological characteristics of the SQ fascial band may reflect the composite mechanical forces experienced by the body part.

Figure 1. Three test segments with ultrasound image samples.

(A) Illustration of ultrasound scanning longitudinal to the long axis of the extremities; (B) The locations where images were obtained: arm (left), calf (middle) and thigh (right); (C). Sample of ultrasound image; (D). Zones demarcated by color: dermal zone (red), SQ zone (yellow), epimysium zone (blue) and muscular zone (green); (E). Binary image with a pixel intensity threshold of 90.

Figure 2. Determination of pixel intensity threshold by principal component analysis.

(A). Eigenvectors of 22 decade variables plotted with respect to two principal components; (B). Value of cos(α) with respect to decade variables: α represents the angle formed between vector 1 (vector sum of all decade variables below designated decade variable) and vector 2 (vector sum of all decade variables above designated decade variable). (see text for detail).

Figure 3. Ultrasound images showing the morphological characteristics of fascial bands.

(A). Ultrasound images from calf, arm and thigh; (B). Three dimensional reconstruction of a video sweep, visualized from two different perspective angles.

Figure 4. Ultrasound images showing the subcutaneous blood vessels encapsulated by fascial bands.

(A). From the site of thigh; (B). From the site of calf ; (C) From the site of arm; (D). Three-dimensional reconstruction of a site with a vessel.

Figure 5. Body-location dependence of SQ zone variables with pairwise comparisons.

Figure 6. Bivariate linear fit between SQ zone variables.

Figure 7. Bivariate linear fit between SQ coherence and various SQ zone variables.

Green represents the data from arm, red from thigh and blue from calf.