RT Journal Article T1 Fetal Development of the Human Obturator Internus Muscle With Special Reference to the Tendon and Pulley A1 Naito, Michiko A1 Suzuki, Ryoji A1 Abe, Hiroshi A1 Rodríguez Vázquez, José Francisco A1 Murakami, Gen A1 Aizawa, Shin AB To examine the development of the tendon pulley of the obturator internus muscle (OI), we observed paraffin sections of 26 human embryos and fetuses (∼6-15 weeks of gestation). The OI was characterized by early maturation of the proximal tendon in contrast to the delayed development of the distal tendon. At 6 weeks, the ischium corresponded to a simple round mass similar to the tuberosity in adults. At 8 weeks, before development of the definite lesser notch of the ischium, initial muscle fibers of the OI, running along the antero-posterior axis, converged onto a thick and tight but short tendon running along the left-right axis. Thus, at the beginning of development, the OI muscle belly and tendon met almost at a right angle. At 10 weeks, the OI tendon extended inferiorly along the sciatic nerve, but the distal part remained thin and loose and it was embedded in the gluteus medius tendon. At 15 weeks, in association with the gemellus muscles, the distal OI tendon was established. The mechanically strong sciatic nerve was first likely to catch the OI muscle fibers to provide a temporary insertion. Next, the ischium developing upward seemed to push the tendon to make the turn more acute along the cartilaginous ridge. Finally, the gemellus muscle appeared to provide inferior traction to the OI tendon for separation from the gluteus medius to create the final, independent insertion. Without such guidance, the piriformis tendon first attached to the OI tendon and then merged with the gluteus medius tendon. PB Wiley SN 1932-8486 SN 1932-8494 YR 2015 FD 2015-02-25 LK https://hdl.handle.net/20.500.14352/109858 UL https://hdl.handle.net/20.500.14352/109858 LA eng NO Naito M, Suzuki R, Abe H, Rodriguez-Vazquez JF, Murakami G, Aizawa S. Fetal Development of the Human Obturator Internus Muscle With Special Reference to the Tendon and Pulley. Anat Rec (Hoboken). 2015 Jul;298(7):1282-93. doi: 10.1002/ar.23121. Epub 2015 Feb 25. PMID: 25683268. DS Docta Complutense RD 18 abr 2025