The twisted structure of the fetal calcaneal tendon is already visible in the second trimester

Abstract

Introduction: The progress in morphological science results from the greater possibilities of intra-pubic diagnosis and treatment of congenital disabilities, including the motor system. However, the structure and macroscopic development of the calcaneal tendon have not been investigated in detail. Studies on the adult calcaneal tendon showed that the calcaneal tendon is composed of twisted subtendons. This study aimed to investigate the internal structure of the fetal calcaneal tendon in the second trimester.

Materials and methods: Thirty-six fetuses fixed in 10% formaldehyde were dissected using the layer-by-layer method and a surgical microscope.

Results: The twisted structure of the calcaneal tendon was revealed in all specimens. The posterior layer of the calcaneal tendon is formed by the subtendon from the medial head of the gastrocnemius muscle. In contrast, the anterior layer is formed by the subtendon from the lateral head of the gastrocnemius muscle. The subtendon from the soleus muscle constitutes the anteromedial outline of the calcaneal tendon. The lateral outline of the calcaneal tendon is formed by the subtendon originating from the medial head of the gastrocnemius muscle. In contrast, the medial outline is formed by the subtendon from the soleus muscle. In most of the examined limbs, the plantaris tendon attached to the tuber calcanei was not directly connected to the calcaneal tendon.

Conclusions: The twisted structure of the subtendons of the fetal calcaneal tendon is already visible in the second trimester and is similar to that seen in adults.

Keywords: Calcaneal tendon; Development; Fetus; Gastrocnemius; Soleus; Tendon.

Fig. 1

The right calcaneal tendon, posterior view, 18 weeks’ gestation: (1) the S-MGC; (2) the S-LGC; (3) the calcaneal tendon just above the tuber calcanei; (4) the tuber calcanei; (5) the S-Sol

Fig. 2

The aponeuroses and the calcaneal tendon (a, b: 13 weeks’ gestation): (1) the medial head of the gastrocnemius muscle; (1a) the S-MGC; (2) the lateral head of the gastrocnemius muscle; (2a) the S-LGC; (3) the soleus muscle; (3a) the S-Sol. The asterisk (*) indicates the deep aponeurosis of the gastrocnemius muscle, which is located on the anterior outline of the muscle belly

Fig. 3

The left calcaneal tendon above the tuber calcanei: (1) posterior view, 14 weeks’ gestation; (2) the medial outline. Black lines mark the rotation of the fibers

Fig. 4

The right calcaneal tendon, posterior view, 19 weeks’ gestation: (1) medial head of the gastrocnemius muscle; (1a) the S-MGC; (2) lateral head of the gastrocnemius muscle; (2a) the S-LGC; (3) the soleus muscle; (3a) the S-Sol; (4) the tuber calcanei

Fig. 5

The left calcaneal tendon, posterior view, 15 weeks’ gestation: (1) the medial head of the gastrocnemius muscle; (1a) S-MGC; (2) the lateral head of the gastrocnemius muscle; (3) the soleus muscle; (3a) the S-Sol; (4) the tuber calcanei

Fig. 6

The right calcaneal tendon, posterior view, 13 weeks’ gestation: (1) medial head of the gastrocnemius muscle; (1a) the S-MGC; (2a) the S-LGC; (3) the soleus muscle; (3a) the S-Sol; (4) the tuber calcanei. The asterisk (*) indicates the surgical forceps

Fig. 7

The right calcaneal tendon, posterior view, 15 weeks’ gestation: (1) the medial head of the gastrocnemius muscle; (1a) the S-MGC; (2) the lateral head of the gastrocnemius muscle; (2a) the S-LGC; (3) the soleus muscle; (3a) the S-Sol; (4) the tuber calcanei

Fig. 8

Horizontal section through the midportion of the fetal calcaneal tendon: (1) the S-MGC; (2) the S-LGC; (3) the S-Sol; (4) the deep calcaneal bursa; (5) Kager’s fat pad. The outlines of the calcaneal tendon: (a) anterior; (b) posterior; (c) medial; (d) lateral