In microneurosurgical procedures, continuous precise procedures are required to provide high-quality surgical results. Stabilizing the surgeon’s arm with an armrest during surgery is expected to improve the precision of microsurgical procedures.1 A freely movable armrest (FMA) was developed to support the surgeon’s hand during surgery2; however, it has not been widely used because it requires continuous manual user interaction.1,2 We have developed a new intelligent armrest using robotics technology. This system was designed so that the arm holder follows the surgeon’s arm and fixes in the adequate position automatically. Here, we describe this system in detail and present preclinical and clinical results.
Concept of the Arm-Holding Device
We produced a prototype model to fulfill our requirements, which we called EXPERT (Figure 1). EXPERT consists of an arm holder, a holder support, and a base. The arm holder is made from the thermoplastic polymer Ortholen, which is widely used in prosthetic limbs. It has a curved shape and holds the surgeon’s forearm. Three small electric magnets are set in the arm holder. A 6-axis force sensor is set between the arm holder and the holder support. The holder support has 5 degrees of freedom. No electric motors are used in the holder support. Each joint has springs and/or counterweights, electric brakes, and encoders. The base has 3 wheels to stand and move the EXPERT system. The system is attached to the operator’s chair (Micro Chair, Mizuho Ikakogyo Co, Ltd, Tokyo, Japan) at the base; it is independent of the height adjustment of the chair but follows the forward/backward movement of the chair.
EXPERT has 3 working modes: the transfer, arm-holding, and arm-free modes, which are converted automatically by analyzing the signals from 6-axis force sensor and the encoders in each joint. There is no need to press any buttons or switches to change modes. The surgeon wears a ferromagnetic wristband that connects to the electric magnets in the arm holder beneath sterile clothing. In the transfer mode, the electric brakes are released and electromagnets are active, so that the arm holder follows the surgeon’s arm from below. The movement is achieved by the magnetic force between the surgeon’s arm and the arm holder. The power required to move the arm holder is < 50 N. Most of the power is transferred to the upper side by springs, and the system reduces the surgeon’s arm weight in the transfer mode. The force to move horizontally is < 50 N. In the arm-holding mode, the arm holder maintains the position by locking the electric brakes and supports the surgeon’s arm weight. When the surgeon moves his/her arm away from the arm holder, eg, to change surgical instruments or to move the operating microscope, it is in the arm-free mode. The arm holder maintains its position by locking the electric brakes. When there is no arm on the arm holder and the unit is in transfer mode, the arm holder moves away from the patient.
Simulated microneurosurgery, involving suturing a thin piece of rubber, was used to examine the use of EXPERT. One quarter of a 10-mm circle was incised in thin pieces of rubber 4 cm in diameter. This circle was placed in a bowl at a depth of 60 mm. The conical working space was formed by plastics in the center of the bowl, which was 55 mm in diameter at the surface and a 10- to 20-mm ellipse at greater depths. Five sutures with 10-0 nylon were put in the incised rubber at even intervals using an operating microscope with conventional surgical instruments (Figure 2). EXPERT was set on the right side of the operator’s chair. Six experienced neurosurgeons were registered as test candidates. Three of the 6 evaluating neurosurgeons (T.G., K.H., T.Y.) are included as authors; the others are colleagues in our department. They practiced the task and use of EXPERT adequately beforehand. The task was carried out once with and once without EXPERT. In each task, performance time to complete suturing was recorded, and each test candidate was asked to give 3 subjective evaluations regarding hand tremor, fatigue, and impression of maneuverability. Subjective evaluations were scored on a visual analog scale in which 1 is the minimum fatigue and the worst to perform and 100 is the maximum fatigue and the best to perform.
The data were analyzed by paired t test. P < .05 was taken to indicate statistical significance.
All tasks were performed successfully without mechanical error of the EXPERT system. The performance time and subjective evaluation score are summarized in Figure 3. Four of 6 test candidates showed shorter performance time with EXPERT. The performance time was not different with and without the EXPERT for the remaining 2 test candidates. All 6 test candidates reported lower scores of fatigue when using EXPERT. The maneuverability score was higher with EXPERT. Recorded video showed that hand tremor of each test candidate was reduced and manipulation was more stable with EXPERT.
Since March 2010, EXPERT has been clinically applied in 13 surgeries at Shinshu University Hospital. Before surgery, clinical application of EXPERT had been approved by the ethics committee of Shinshu University School of Medicine, and informed consent was obtained from all patients and their families. After the usual preparation of craniotomy and dura opening, EXPERT, covered with a sterile sheet, was introduced into the operative field. A surgeon performed the operation with routine microneurosurgical procedures supported by the EXPERT system (Figure 4). The surgeons did not always use EXPERT because rapid procedures without stringent accuracy requirements could be performed easily without the system. There were no complications related to the use of EXPERT.
To provide high-quality surgical results, continuous precise motions are required in microneurosurgery. Precise movements can be achieved by maneuvering the surgical instruments with adequate stabilization of the surgeon’s arm at the appropriate position. This has been achieved in conventional microneurosurgery by resting the surgeon’s arm, hand, or finger on the patient’s body or craniotomy edge and on the armrest of the surgical chair and a part of the head fixation frame.3-10 The rigid, fixed-type armrest can be introduced easily but cannot completely cover the work space because many factors limit the surgeon’s hand position. The brain surface cannot be touched or compressed by the surgeon’s hand or arm. It is necessary to change the positions of brain spatula and self-retaining brain retractors frequently during surgery. The direction and angle of surgical instruments restricted by surrounding structures also limit the surgeon’s hand position.
An armrest with positions that can be changed as required is called an FMA and is considered effective. Ohta and Kuroiwa2 developed the FMA (Smartarm, Mizuho Ikakogyo Co, Ltd, Tokyo, Japan) and reported its usefulness in neurosurgery. There is no doubt that the use of an FMA reduces operator fatigue and improves surgical maneuverability. We had also reported that the use of an FMA gave the operator a more relaxed posture and reduced both muscle stress and hand tremor compared with the use of a conventional armrest system.1 Use of the FMA will reduce tremor when fine microsurgical movement is performed and thus will provide a good surgical result. Even if the surgeon can perform fine microsurgical movement without assistance of the FMA, more precise procedures can be performed with the FMA.
Despite its advantages for precise procedures, FMA-assisted surgery has not been widely adopted because its use is time-consuming and adjustment can be difficult. When the surgeon wishes to adjust the position of the FMA, eg, the Smartarm, it is necessary to put down the surgical instrument, push the button to change from locking to moving mode, adjust the position at which the arm is held, release the button to return from locking mode to moving mode, and retrieve the surgical instrument. These actions are time-consuming and troublesome. The optimal position of the surgeon’s arm changes frequently, so real adjustment of the armrest to the optimal position may be impossible. The surgeon can identify the optimal position of the armrest while holding the surgical instrument in his/her hand and watching the operative view. When the position of armrest is incorrect, the adjustment action must be repeated. Therefore, the surgeon may continue the procedure even if the position of the arm holder is not adequate.
EXPERT is classified as a type of FMA. However, EXPERT differs from an FMA in that it automatically follows the surgeon’s arm. The surgeon can change the position of the armrest while using the microscope and can continue the microsurgical procedure while holding the surgical instrument. There is no need to push any buttons to convert between the lock and free modes. We believe that most disadvantages associated with the use of previous FMAs can be reduced by these functions of the EXPERT system.
Cost-effectiveness is also an important factor in widespread adoption. EXPERT is a surgeon support system and does not touch the patient. EXPERT is in the same equipment category as operating bed and operating chair and thus has no need for a clinical trial before commercial production. The potential commercial cost of EXPERT should be reasonably low.
Further improvement of EXPERT is necessary. The usefulness of EXPERT has been confirmed with only the right hand; however, using EXPERT with both hands may yield better results in microneurosurgery. The space occupied by EXPERT is also a problem because many surgical tools such as the operative microscope, navigation systems, drilling system, and coagulation system must be set near the surgeon. The base of EXPERT is large and heavy to prevent the system from falling or toppling over. Reducing the size of the EXPERT system while maintaining its functionality is a necessary future development. There is a tight feeling during transposition of the surgeon’s arm because the supporting part must move automatically with the surgeon’s hand motion.
The success of da Vinci surgical systems incited a dream to apply master-slave configured surgical robots in all surgical fields. Thus, the NeuRobot was developed for microneurosurgery.11-13 From the experience with NeuRobot, we determined the difficulty of using surgical robots for microneurosurgery. Microneurosurgery is a fine art that only the human hand can produce. EXPERT provides support for a surgeon’s art by allowing smooth and steady movement.
The intelligent armrest EXPERT held the surgeon’s arm comfortably and followed the surgeon’s arm automatically. EXPERT represents a useful tool for microneurosurgery. However, several modifications are required for commercial development of this system.
This project was supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology Grant-in-Aid for Scientific Research No.19200043 (Dr Hongo). The arm holder was made by Arizonoseisakusyo Co, Ltd Japan. The holder supporting part and basal part was made by Hitachi JTE Co, Ltd, Japan. The surgical drape was made by Hogi Co, Ltd, Japan. There was no financial support from any companies. The main features of this system were already opened for patent in Japan No. 2008-151906 L0800004. Shinshu University and Waseda University preserve all rights without relevant company and individual persons. The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.
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