Structure of the Achilles tendon at the insertion on the calcaneal tuberosity

Abstract

Findings on the twisting structure and insertional location of the AT on the calcaneal tuberosity are inconsistent. Therefore, to obtain a better understanding of the mechanisms underlying insertional Achilles tendinopathy, clarification of the anatomy of the twisting structure and location of the AT insertion onto the calcaneal tuberosity is important. The purpose of this study was to reveal the twisted structure of the AT and the location of its insertion onto the calcaneal tuberosity using Japanese cadavers. The study was conducted using 132 legs from 74 cadavers (mean age at death, 78.3 ± 11.1 years; 87 sides from men, 45 from women). Only soleus (Sol) attached to the deep layer of the calcaneal tuberosity was classified as least twist (Type I), both the lateral head of the gastrocnemius (LG) and Sol attached to the deep layer of the calcaneal tuberosity were classified as moderate twist (Type II), and only LG attached to the deep layer of the calcaneal tuberosity was classified as extreme twist (Type III). The Achilles tendon insertion onto the calcaneal tuberosity was classified as a superior, middle or inferior facet. Twist structure was Type I (least) in 31 legs (24%), Type II (moderate) in 87 legs (67%), and Type III (extreme) in 12 legs (9%). A comparison between males and females revealed that among men, 20 legs (24%) were Type I, 57 legs (67%) Type II, and eight legs (9%) Type III. Among women, 11 legs (24%) were Type I, 30 legs (67%) Type II, and four legs (9%) Type III. No significant differences were apparent between sexes. The fascicles of the Achilles tendon attach mainly in the middle facet. Anterior fibers of the Achilles tendon, where insertional Achilles tendinopathy is most likely, are Sol in Type I, LG and Sol in Type II, and LG only in Type III. This suggests the possibility that a different strain is produced in the anterior fibers of the Achilles tendon (calcaneal side) where insertional Achilles tendinopathy is most likely to occur in each type. We look forward to elucidating the mechanisms generating insertional Achilles tendinopathy in future biomedical studies based on the present results.

The Twist of the Achilles Tendon – Associations of Torsions in the Lower Extremity

“…We used two methods, an established one, described by van Gils et al (), and a new one based on quantitively measuring the different torsion angles using an open‐source computer software. Although the new data does not integrate well with the data of van Gils et al (), a certain degree of accordance with newer data of Edama et al (, ) could be found. Furthermore, the correlation of the torsions could only be identified after including all parts of the triceps surae muscle.…”

“…Looking at the LG, for example, a strong positive, i.e., outward or lateral, respectively, the rotation was seen in some specimens. This might correspond to the “moderate” (Type II) and “extreme” (Type III) rotation types seen in the study by Edama et al (, ). Accordingly, when the LG rotated outwardly, the MG also showed a slight outward rotation.…”

“…A torsion of the AT is well described in the literature, albeit, there has been little agreement about the degree of torsion (Cummins et al, 1946;Schonbauer, 1986;van Gils et al, 1996;Schepsis et al, 2002;Robert, 2008;Szaro et al, 2009). Although recent studies (Edama et al, 2015a(Edama et al, , 2016 have attempted to provide answers to this question, surprisingly, the matter has only been investigated in an isolated manner yet. Clark (1972) described an angle of <2 in newborns, which stands in certain contrast to the to date described angles in adults.…”

“…The reasons for this remain largely unknown, but poor blood supply and uneven biomechanical strain of this part have been proposed to play important roles (Schonbauer, ; Kannus and Jozsa, ; Roberts and Deliss, ; Theobald et al, ; Hess, ). Both these factors cannot be viewed in isolation but are likely to be associated with the special twisted structure of the AT (Bojsen‐Moller and Magnusson, ; Edama et al, )…”

“…The reasons for this remain largely unknown, but poor blood supply and uneven biomechanical strain of this part have been proposed to play important roles (Schonbauer, 1986;Kannus and Jozsa, 1991;Roberts and Deliss, 2002;Theobald et al, 2005;Hess, 2010). Both these factors cannot be viewed in isolation but are likely to be associated with the special twisted structure of the AT (Bojsen-Moller and Magnusson, 2015; Edama et al, 2016) Studies have come to the general conclusion that some kind of torsion exists, however, the reported degree of the torsion varies greatly. An early study by Cummins et al (1946) reported only types of torsions based on visualization of the soleus (Sol) and the whole of the gastrocnemius muscle, as did Szaro et al (2009).…”