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Although previous studies have reported fatty infiltration of the gastrocnemius–soleus complex, little is known about the volumetric distribution and patterns of fatty infiltration. The purpose of this anatomical study was to document and quantify the frequency, distribution, and pattern of fatty infiltration of the gastrocnemius–soleus complex. One hundred formalin‐embalmed specimens (mean age 78.1 ± 12.3 years; 48F/52M) were serially dissected to document the frequency, distribution, and pattern of fatty infiltration in the medial and lateral heads of gastrocnemius and soleus muscles. Fatty infiltration was found in 23% of specimens, 13 unilaterally (8F/5M) and 10 (5M/5F) bilaterally. The fatty infiltration process was observed to begin medially from the medial aspect of the medial head of gastrocnemius and medial margin of soleus and then progressed laterally throughout the medial head of gastrocnemius and the marginal, anterior, and posterior soleus. The lateral head of gastrocnemius remained primarily muscular in all specimens. Microscopically, the pattern of infiltration was demonstrated as intramuscular with intact aponeuroses, and septa. The remaining endo‐, peri‐, and epimysium preserved the overall contour of the gastrocnemius–soleus complex, even in cases of significant fatty replacement. Since the external contour of the calf is preserved, the presence of fatty infiltration may be underdiagnosed in the clinic without imaging. Myosteatosis is associated with gait and balance challenges in the elderly, which can impact quality of life and result in increased risk of falling. The findings of the study have implications in the rehabilitation management of elderly patients with sarcopenia and myosteatosis. [ABSTRACT FROM AUTHOR]

Objectives: The elaborate morphometry of the human trapezius muscle facilitates its involvement in numerous active movements of the shoulder girdle and passive stabilization of the upper extremity. Despite its functional importance throughout the lifespan, little is known about the 3D architecture of trapezius at any post-natal timepoints. Accordingly, the aim of this preliminary cadaveric study was to digitize, quantify, model, and compare the 3D architecture of trapezius at two temporal extremes: infancy and adulthood. Methods: We examined trapezius in two female formalin-embalmed cadavers, aged 6 months and 72 years, respectively. We meticulously dissected each muscle, allowing us to digitize and model the comprehensive muscle architecture in situ at the fiber bundle level. We quantified standard architectural parameters to facilitate comparison between each functional partition of trapezius (i.e., descending, transverse, ascending) and proportionally between the infant and adult specimens. Results: We found markedly different patterns in fiber bundle length range, physiological cross-sectional area, and muscle volume within and between muscles. Notably, the proportional physiological cross-sectional area of the ascending and descending partitions was equal (1:1) in the infant, in contrast to 3:1 in the adult. The transverse partitions were proportionally similar, accounting for over half of the whole muscle physiological cross-sectional area in both specimens. Conclusion: This study provides preliminary insights into infant and adult trapezius architecture at an unparalleled level of detail and precision. The quantifiable architectural differences appear to coincide with functional development-a notion that warrants further investigation in larger samples and with longitudinal approaches. [ABSTRACT FROM AUTHOR]

Physiological cross-sectional area (PCSA) is used to compare force-producing capabilities of muscles. A limitation of PCSA is that it cannot be measured directly from a specimen, as there is usually no area within the muscle traversed by all fibres. Traditionally, a formula requiring averaged architectural parameters has been used. The purpose of this paper is to describe the development of a fibre bundle element (FBE) method to calculate PCSA from digitised fibre bundle data of five architecturally distinct muscles and compare the FBE and PCSA formula. An FBE method was developed that used a serially arranged set of cylinders as the volumetric representation of each fibre bundle, and PCSA was computed as the summation of the cross-sectional area of each FBE. Four of five muscles had significantly different PCSA between FBE and formula methods. The FBE method provides an approach that considers architectural variances while minimising the need for averaged architectural parameters. [ABSTRACT FROM AUTHOR]