Fetus Support Manipulator with Flexible Balloon-based Stabilizer for Endoscopic Intrauterine Surgery

A novel manipulator is described for stabilizing fetus and preventing it from free-floating during the endoscopic intrauterine surgery. Minimally invasive endoscopic fetal surgery enables intrauterine intervention with reduced risk to the mother and fetus. We designed and fabricated a prototype of a fetus supporting manipulator equipped with a flexible bending/curving mechanisms and a soft balloon-based stabilizer. The flexible bending and curving mechanisms enable the stabilizer to reach the target sites within the uterus under an ultrasound-guidance. The balloon-based stabilizer could be inserted into the uterus with a small incision for entry. The accuracy evaluation showed that the maximum error of the curving mechanism was as small as 7 mm and the standard deviation of the bending mechanism was 1.6 degree. In the experiments using a fetus model, the manipulator could be well controlled under ultrasound guidance and its curving mechanism with the balloon-based stabilizer could be clearly visualized during the implementation of fetus model supporting. The manipulator has the potential to be used in minimally invasive intrauterine surgery, though further improvements and experiments remain to be carried out.


1. Fetus stabilizing mechanism and manipulator system for intrauterine surgery
In recent years, endoscopic technology has provided a less invasive approach to surgical treatment. Minimally invasive endoscopic fetal surgery enables intrauterine intervention with reduced risks to the mother and fetus. The problem is that the fetus is floating in the amniotic fluid and its movement will disturbe the surgical treatment. Then, it is necessary to develop a fetus-holding device to support the fetus within the uterus. In a previous research, we attempted to develop a stainless steel fetal stabilizer. The outcome of this research was unfavorable although the fetus was fixed well. Other device was a suction type silicone tube stabilizer equipped with small holes to apply negative pressures on the fetal skin. However, this device was likely to cause fetal tissue congestion during a long time surgery. To overcome these issues, we propose a newly-developed manipulator with a flexible mechanism and a balloon-based supporting stabilizer. The outcome of mechanical performance tests and surgical practice tests using a fetal model under ultrasound guidance will be also described.
The prototype of the fetal support manipulator is comprised of three units: the flexible manipulator unit with a balloon-based stabilizer and a curving mechanism; the PC for controlling the bending mechanism and the syringe; the ultrasonic device for viewing the intra-operative situation of the fetus and the instrument．In general endoscopic surgery, since the viewing zone of endoscope is small and sometime the endoscope can not reach the narrow area, an ultrasonic image is used for assisting the endoscope surgery. The ultrasound is an ideal imaging modality for the diagnosis in obstetrics and gynecology. We use ultrasound to acquire the real-time intra-operative information. The position of the fetus and the umbilical cord could be identified when we insert the stabilizer into the uterus.
Fig.1 Fetus support manipulator system for intrauterine surgery．

2. Mechanism of the manipulator and stabilizing procedure
The procedure of inserting the balloon-based stabilizer to the uterus and stabilizing the fetus with the ultrasound guidance. 1) We insert the instrument with a shrunk balloon according to the position of the fetus. The spatial relationship of the fetus, the uterine wall and the instrument is observed using an ultrasonic diagnosis device. 2) The bending angle of the link part and the curving part of the manipulator are controlled by a PC according to position of the fetus. The bending and curving mechanisms are crooked and inserted into the required position with the guidance of intra-operative ultrasonic image.3) When the silicon covered curving part arrive the abdomen of the fetus, we inject the physiological saline into the balloon and adjust the balloon to optimal position for stabilizing the fetus.