Fetal development of the pulley for muscle insertion tendons: A review and new findings related to the tensor tympani tendon.
The existence of hard tissue pulleys that act to change the direction of a muscle insertion tendon is well known in the human body. These include (1) the trochlea for the extraocular obliquus superior muscle, (2) the pterygoid hamulus for the tensor veli palatini muscle, (3) the deep sulcus on the plantar aspect of the cuboid bone for the peroneus longus tendon, (4) the lesser sciatic notch for the obturator internus muscle, and (5) the bony trochleariformis process for the tensor tympani muscle tendon. In addition, (6) the stapedius muscle tendon shows a lesser or greater angulation at the pyramidal eminence of the temporal bone. Our recent studies have shown that the development of pulleys Nos. 1 and 2 can be explained by a change in the topographical relationship between the pulley and the tendon, that of pulley No. 3 by the rapidly growing calcaneus pushing the tendon, and that of pulley No. 4 by migration of the insertion along the sciatic nerve and gluteus medius tendon. Therefore, in Nos. 1-4, an initially direct tendon curves secondarily and obtains an attachment to the pulley. In case No. 6, the terminal part of the stapedius tendon originates secondarily from the interzone mesenchymal tissue of the incudostapedial joint. In the case of pulley No. 5, we newly demonstrated that its initial phase of development was similar to No. 6, but the tensor tympani tendon achieved a right-angled turn under guidance by a specific fibrous tissue and it migrated along the growing malleus manubrium.
Institute of Embryology, Department of Anatomy and Human Embryology, Faculty of Medicine, Complutense University, Madrid, Spain.
Jose Francisco
JF
Rodríguez-Vázquez
Department of Otolaryngology-Head & Neck Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan. Electronic address: y-honkura@orl.med.tohoku.ac.jp.
Yohei
Y
Honkura
Department of Otolaryngology-Head & Neck Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan.
Yukio
Y
Katori
Division of Internal Medicine, Iwamizawa Kojin-kai Hospital, 297-13 Shibuncho, Iwamizawa, Hokkaido 068-0833, Japan.
Gen
G
Murakami
Department of Anatomy, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
Hiroshi
H
Abe
D047108:Embryonic Development / Q000502:physiology*; D006801:Humans; D013710:Tendons / Q000033:anatomy & histology / Q000196:embryology / Q000254:growth & development; D013719:Tensor Tympani / Q000033:anatomy & histology / Q000196:embryology / Q000254:growth & development
Development; Human fetus; Pulley; Tendon; Tensor tympani