A review of wrist mechanism design and the application in gastrointestinal minimally invasive surgery of multi-degree-of-freedom surgical laparoscopic instruments

Abstract

Background

This paper aims to comprehensively review current designs of Multi-degree-of-freedom (Multi-DOF) wrist mechanisms and the applications of Multi-DOF surgical instruments in gastrointestinal minimally invasive surgery (MIS).

Methods

By reviewing the advantages and limitations of traditional laparoscopic and robotic surgical instruments, we present the development of Multi-DOF surgical instruments. Then, we summarize the Multi-DOF wrist mechanisms, delineating their pros and cons. Finally, the surgical outcomes and efficiency of Multi-DOF surgical instruments are reviewed.

Results

The utilization of Multi-DOF surgical instruments for both benign and malignant gastrointestinal diseases demonstrates perioperative outcomes comparable to traditional laparoscopic and robotic surgeries. In certain aspects, it exhibits advantages such as shorter operative times and faster gastrointestinal function recovery.

Conclusion

Further research is needed to effectively combine these driving mechanisms to achieve a new type of transmission mechanism with high rigidity and precision, ample working space, and decoupled degrees of freedom. Multi-DOF surgical instruments offer the advantages of high flexibility and lower costs, displaying good feasibility and safety in practical clinical applications within gastrointestinal surgery. Their promotion in primary care hospitals could benefit a larger patient population. However, more extensive sample-sized multicenter studies are still warranted to elucidate such surgical instruments’ advantages further.

Compared to traditional open surgery, laparoscopic surgery has been widely adopted as a safe and viable alternative due to its advantages, such as smaller incisions, less trauma, quicker postoperative recovery, reduced postoperative pain, and shorter hospital stays, since its inception. This adoption has significantly propelled the development of MIS techniques. However, some drawbacks have been identified in its practical clinical application. Due to the rigidity and straight shape of laparoscopic surgical instruments, the end effectors cannot bend, which increases the difficulty of surgery when separating deep tissues or operating in narrow spaces. This challenge led to the development of robotic surgery systems, which address some of the limitations associated with traditional laparoscopic surgery. These systems provide three-dimensional visualization, filter hand tremors, and feature end effectors with multiple degrees of freedom, enabling more precise maneuvers. However, their wrist components are often cable-driven, leading to joint gap issues, cable slack, and motion lag, resulting in cable fatigue, breakage, reduced structural rigidity, significant deformation, and decreased motion reliability [1]. Robotic surgical instruments must be mandatorily replaced after a limited number of uses. Moreover, the high manufacturing and maintenance costs limit their dissemination and use in economically underdeveloped regions. Additionally, the lack of tactile feedback can lead to an inability to sense the magnitude of tensile stress during surgery, potentially causing unnecessary injury. Therefore, combining the advantages of traditional laparoscopic instruments and robotic surgery systems to develop multi-degree-of-freedom surgical instruments that offer high flexibility similar to robotic instruments at a lower cost has become a current research focus.

Traditional laparoscopic surgery

In 1994, Kitano et al. [2] applied laparoscopy to distal gastrectomy for gastric cancer. Compared with traditional open surgery, the dominant benefits of Laparoscopic surgery are less abdominal trauma and postoperative pain, quicker return of normal gastrointestinal function and oral intake, less postoperative nausea and vomiting, and shorter hospital stay [3]. However, traditional laparoscopic surgery has encountered many significant challenges during the past two decades of application related to the instrument itself. Hand-held laparoscopic devices are long and rigid, generally without a wrist joint at the end effector [4]. In addition, the pivot point created by the abdominal wall reverses the motion of the handle with that of the end effector, which is counterintuitive. This "fulcrum effect" makes it more difficult for surgeons to master laparoscopic techniques [5]. For these reasons, the suture of important vessels and tissue, an essential aspect of MIS, is a sophisticated surgical skill and perhaps the most challenging part of minimally invasive surgical reconstruction [6].

Although laparoscopically assisted distal gastrectomy (LADG) is superior to open traditional gastrectomy in certain aspects, the reduction in the number of recovered lymph nodes and the prolongation of operation time is a deficiency of this method [7]. The wide application of laparoscopic surgery in the treatment of advanced gastric cancer is limited, mainly attributed to the complexity of vascular anatomy and the technical limitations of traditional laparoscopic instruments, which makes D2 lymph node dissection difficult even for well-trained surgeons. In the meanwhile, massive bleeding may occur during the dissection around the hepatic, celiac, and splenic arteries [3, 8].

Compared with LADG, laparoscopically assisted total gastrectomy (LATG) is not widely accepted by the community. In particular, the operation has given rise to concerns about the complexity confronted in complex reconstruction of the digestive tract, such as esophagojejunostomy, and potentially severe complications. Compared with the traditional open gastrectomy, the absence of tactile sensation, longer anesthesia and operation time, and insufficient resection rate also make the operation challenging [3, 9].

Robot-assisted laparoscopic surgery

With the development of engineering and medicine, several traditional open surgery operations have already been replaced by minimally invasive surgery, which shortens the days of hospital stay, diminishes the volume of bleeding, decreases the formation of postoperative scars, leads to pain relief and prevents severe postoperative complications [10, 11]. However, on the other hand, the direct vision contact with the surgical site disappears and the operating space of surgical instruments is reduced, which are some shortcomings of MIS. In addition, Surgeons can make full use of their dexterous, specially trained hands and wrists when they perform open surgery. On the contrary, this ability is extremely hindered in MIS because of traditional laparoscopic instruments without joint-connected wrists, and the lack of freedom declines the flexibility of MIS surgical instruments [4, 12, 13]. Therefore, the learning process of MIS is more challenging than traditional open surgery. To eliminate these defects, robot-assisted minimally invasive surgery (RMIS) has been developed. One of the key functions provided by the robot system is the tiny mechanical wrist. The capability of macro‐micro manipulation with redundant degrees of freedom (DoF > 6), compared to the limited degree of freedom of traditional laparoscopic instruments, allows these robot systems to perform sophisticated operations in the surgical area by improving flexibility [4, 14–16].

Robotic surgery facilitates overcoming the technical limitation of traditional laparoscopy in digestive tract reconstruction after total gastrectomy, in that even in deep and narrow spaces, robotic systems can provide surgeons with precise sutures that traditional laparoscopic instruments cannot achieve. In particular, for hand-held devices that lack wrists, the closed axis of the incision can be sutured directly when the axis of the incision is roughly aligned with the axis of the laparoscopic tool. In contrast, it is an overwhelming and challenging task to stitch an incision perpendicular to the instrument axis. In surgery, however, sutures are typically required perpendicular to the instrument axis [3, 4].

In numerous studies, laparoscopic gastrectomy is reportedly superior to open gastrectomy. Thus, conceivably, optimal perioperative surgical outcomes may have already been achieved with laparoscopic surgery, leaving little room for improvement via robotic surgery. To better demonstrate the benefits of robotic surgery over laparoscopy, researchers should focus on the impact of the robotic system on procedures that are technically demanded by laparoscopy rather than those that are relatively simple [17].

It is widely believed that D2 lymph node dissection is a more critical part of minimally invasive gastrectomy [3]. Regarding the technical aspects, laparoscopic systematic D2 lymphadenectomy is complicated, particularly in the dissection of the perigastric lymph nodes along the major curvature and the second tier nodes along the celiac and splenic arteries. Large vessels have to be identified and extensive lymph node dissection has to be performed. [8]. As a result of its prominent technical superiority in the dissection of lymphoid tissue around the portal vein, common hepatic artery, celiac trunk, and splenic artery, D2 lymph node dissection can become the primary indication of robot-assisted surgery [3]. In these areas, the EndoWrist function, offering redundant freedom, allows surgeons to reach these deep areas that traditional laparoscopic straight forceps cannot reach. For example, during a gastric operation, the splenic artery lymph nodes (station 11p) are located in the dorsal plane; the convex body of the pancreas often interferes with laparoscopic instruments and hinders surgeons from performing accurate dissection. Even if the pancreas is overpressed downward, it is difficult to effectively reach the posterior side of the supra pancreatic lymph node area, which is possible to cause pancreatic damage and pancreatitis. The robot-assisted technique makes it easier to accomplish this phase laparoscopically, as robotic instruments can easily overcome this typical laparoscopic drawback when the dissection is driven circumferentially around the major vessels [3].

Robot-assisted surgery provides patients with the benefits of hand-held laparoscopic surgery without the disadvantages of bulky and counterintuitive traditional tools. RAS gives surgeons more degrees of freedom, negates the fulcrum effect, and suppresses hand tremors [18].

New multi-degree-of-freedom articular laparoscopic surgical instruments

Conventional MIS instrument consists of an end effector, rigid shaft and handle, and has only 4 degrees of freedom (DoFs) as shown in Fig. 1a. The 4 DoFs are 1) linear motion along the axis of the shaft, 2) rotation about the axis of the shaft, 3, 4) pivoting motion at the instrument port [19]. Due to the pivot point, the two rotations (yaw and pitch) are usually limited to 120, which prevents the complete rotation of the end effector [20]. Compared with the 6 degrees of freedom in open surgery, this limitation of four degrees of freedom of traditional laparoscopic instruments makes it more difficult to perform simple operations in surgery and hinders many surgeons from performing various minimally invasive manipulations and operations [21]. Since the port restricts accessibility to the surgery target, engineers have developed flexible and steerable end effectors to add 2 DoFs to the instruments, generally pitch and yaw as shown in Fig. 1b [19].

Fig. 1.

Comparison of direction of freedom between a conventional MIS instrument with 4 DoFs and b a dexterous MIS instrument with 6 DoFs [19]

The robotic system, such as EndoWrist of da Vinci, was developed by Intuitive Surgical, USA. They have two extra degrees of freedom on the wrist (wrist deflection and wrist Pitch), permitting the end effector to rotate 360 degrees [22]. However, compared with laparoscopic surgery, robotic minimally invasive surgery has no cost-effective advantage for patients or hospitals. Other existing deficiencies of robot-assisted laparoscopy include the absence of tactile sensation, lack of tissue tension, and increased surgery time, which are more likely to result in undesirable injury. In addition, so far, robotic surgery has not been proven to be superior to traditional laparoscopic surgery because of the need for long-term oncology equivalence data [3, 4, 21]. As a result, both academic and commercial institutions are interested in creating lower-cost devices that provide some advantages of these robotic surgical platforms, filling the space between traditional surgical instruments and surgical robots. In this case, innovative handheld laparoscopic devices have emerged [22]. The development of new laparoscopic devices by increasing the flexibility of traditional laparoscopic instruments in possible joints is already under study. The primary purpose behind this method is to invent a compact and low-cost laparoscopic surgical instrument that will realize tip point maneuverability similar to the robotic instrument (Fig. 2) [16].

Fig. 2.

Classical (left) and robotic (right) laparoscopic forceps [16]

The significant difference between hand-held surgical instruments and telemanipulated surgical systems such as da Vinci is that handheld devices provide tactile feedback during surgery [22]. The distinction between traditional laparoscopic instruments and articulated instruments (ALIs) lies in the Multi-DOF joints located near the end effectors in the patient’s body [23].

Anderson et al. [23] identified three different ways in which the movement of the surgeon’s hand can be mapped to the motion of the wrist of the device, and reviewed each basic type of mechanical surgical instrument with wrist-like dexterity. Table 1 summarizes the features, advantages and drawbacks of Multi-DOF instruments.

Table 1.

The features, advantages and drawbacks of Multi-DOF instruments [4, 21, 23–32]

Multi-DOF instrument	Feature	Advantage	Drawback
Tuebingen Scientific Radius Surgical System (Tuebingen Scientific Medical GmbH, Tuebingen, Germany)	1. The wrist mechanism is sliding joint 2. Radius is a reusable needle holder with a shaft diameter of 10 mm 3. Radius is slightly shorter than traditional laparoscopic instruments, which are typically 50 cm 4. A hybrid control approach is employed. The wrist deflects unidirectionally with respect to the shaft as the handle is articulated relative to the shaft of the device. Axial rotation of the shaft is achieved through a thumb knob. A large, multi-finger trigger on the handle operates the jaws of the end effector 5. The end effector lacks locking capability 6. The operating mechanism eschews cables, instead utilizing a gear system to deflect and rotate the distal actuator 7. Due to its unique decoupling method of freedom, Radius cannot be categorized as parallel or inverse kinematic mappings	1. Radius possesses physical durability and allows for detachable sterilization, serving as reusable instrumentation 2. Radius mitigates the forced wrist flexion and excessive shoulder and elbow angles characteristic of traditional instruments, which improves safety and ergonomics with this instrument 3. The learning curve for Radius, in comparison to traditional reconstructive laparoscopic surgeries, appears significantly shorter 4. Studies h Multi-DOF instrument ave found that this instrument enhances maneuverability at surgical sites across various procedures	1. The axis diameter may constitute a drawback 2. The tip rotation is less intuitive compared to robotic systems, thus requiring prolonged instrument practice 3. A potential drawback of this design involves the necessity to control one of its degrees of freedom and wrist articulation’s unidirectional deviation using a thumb knob 4. This decoupling of freedom renders the instrument more challenging to use than many other multi-degree-of-freedom instruments (for instance, surgeons must mentally map thumb movements to axis rotations, a mapping absent in different medical devices)
FlexDex (FlexDex Inc., Brighton, MI, USA)	1. The wrist mechanism is rolling joint 2. FlexDex is based on a simple and mechanical design devoid of electronic components 3. FlexDex features a tool rack attached to the user’s forearm, serving as an interface for transmitting motions of the forearm, wrist, and hand to the tip of the instrument, with the wrist joint axis aligned with the surgeon’s wrist center 4. The wrist deviation of the surgeon is translated into wrist deviation within the patient’s body through two transmission belts, resulting in a parallel mapping 5. FlexDex incorporates a pivot joint, whereby the opening and closing motion of the instrument tip are controlled by a thumb lever on the instrument handle. Thus, it allows FlexDex to offer similar degrees of freedom for the surgeon’s wrist.	1.FlexDex does not require wall tension forces to stabilize the instrument shaft 2.FlexDex maps the surgeon’s wrist motions directly to the intraoperative wrist of the instrument at a 1:1 ratio 3. FlexDex intuitively translates the movements of the surgeon’s hand, wrist, and arm 4. FlexDex accomplishes suturing tasks within confined spaces	1. Maneuvering and exchanging instruments might pose challenges and consume time, preventing swift disassembly and replacement in emergencies 2. The tool rack aligns the instrument shaft with the forearm, which may lead to conflicts with other instruments, thereby reducing the options for instrument entry into the patient’s abdominal cavity 3. FlexDex is compatible only with 8-mm trocars 4. Despite being mechanical in nature, FlexDex incurs substantial costs due to its disposable nature 5. Currently, only one needle holder support is available 6. Further research is warranted to assess the reliability and learning curve associated with this instrument
RealHand (Novare Surgical, System, Cupertino, CA, USA)	1. The wrist mechanism is sliding joint 2. RealHand features a shaft diameter of 5 mm, equipped with a pistol-grip handle and wrist control device with a loop 3. The end effector is driven by cables, featuring inverse kinematic mapping, enabling 360-degree articulation and a total of 7 degrees of freedom (DoF) 4. The instrument comprises a cautery, grasper, dissector, and ThermaSeal (for tissue sealing and separation) 5. RealHand incorporates a locking mechanism, allowing it to function as a conventional straight instrument or with multiple DoF 6. A knob is present to enable axial rotation of the end effector independently from the instrument handle itself	1. RealHand can enhance simplicity in single-incision surgery 2. The jaws of the end effector can be locked, which is particularly useful for securely grasping needles during suturing without applying constant handle pressure 3. Studies have assessed the use of this instrument in treating uterine cancer. Results indicate no intraoperative or postoperative complications, with normal blood loss. Surgeons noted that multi-degree-of-freedom instruments appeared to enable more precise lymph node localization 4. The product is commercially mature	1. RealHand is a disposable device with high costs 2. RealHand features a pistol-grip handle with a control point where the handle connects to the tool shaft. This necessitates arcuate sweeping motions of the surgeon’s hand to achieve tip deflection, contributing to a notable learning curve 3. Unnecessary force is applied to the abdominal wall when the instrument shaft is inserted into the patient’s body 4. A study analyzed the joint forces of such flexible instruments and compared them to the actual forces required for procedures involving fixation of the ureter, renal artery, and renal vein. Their findings suggest that the combined forces generated by the joint instrument are insufficient for typical surgical demands
SILSHand (Medtronic, Minneapolis, MN, USA)	1. The wrist mechanism is sliding joint 2. SILS manual instruments offer various articulating surgical devices designed explicitly for Laparoendoscopic single-site surgery(LESS) procedures, including hooks, graspers, scissors, and dissectors, all with a diameter of 5 mm 3. These instruments feature a pistol-grip handle with a wrist-locking mechanism 4. Through inverse kinematic mapping, they provide infinite positioning of dynamic articulation at the tip 5. The instrument shaft can articulate up to 80 degrees, with a knob enabling axial rotation of the distal actuator independent of the instrument handle, while the tip can rotate 360 degrees	1. The jaws of the distal actuator can be locked, which is particularly useful for securely grasping needles during suturing without the need for constant handle pressure 2. This articulated instrument has been widely employed in minimally invasive surgeries such as colon resections, uterine fibroid removals, and partial nephrectomies 3. The product has reached a relatively advanced stage of commercial maturity	1. It is a disposable device with high costs 2. Some argue that achieving distal wrist deflection requires surgeons to sweep their hands through a large arc, rendering the instrument challenging to use and resulting in unnecessary force being applied to the abdominal wall when the instrument shaft is inserted into the patient’s body
Autonomy Laparo Angle (CambridgeEndoscopic Devices, Framingham, MA, USA)	1. The wrist mechanism is soft continuum 2. The instrument design conforms to ergonomic handle shapes, featuring inverse kinematic mapping between the instrument handle and distal actuator, a 5-mm instrument shaft, and a flexible instrument tip 3. Axial rotation of the instrument tip is controlled by a knob mechanism on the handle 4. The distal instrument tip can bend in any direction and rotate 360 degrees at any angle, allowing for 7 degrees of freedom 5. Unlike other flexible instruments used for LESS surgeries, this instrument can rotate, open, and close the distal jaws after locking the instrument	1. The instrument features a wrist-locking mechanism integrated into the handle, reducing muscle fatigue for surgeons when maintaining instrument curvature is necessary 2. The jaws of the distal actuator can be locked, which is particularly useful for securely grasping needles during suturing without the need for constant handle pressure	1. It is a disposable device with a relatively high cost 2. The Autonomy Laparo-Angle instrument features a large and cumbersome handle, which may not be optimal 3. Some argue that achieving distal wrist deflection requires surgeons to sweep their hands through a large arc, rendering the instrument challenging to use and resulting in unnecessary force being applied to the abdominal wall when the instrument shaft is inserted into the patient’s body
Maestro (Vanderbilt University, Nashville, TN, USA)	1. The wrist mechanism is sliding joint 2. The end effector is driven by cables, and the opening and closing actions of the jaws are controlled by squeezing the two handle arms together 3. The instrument includes a jaw-lock mechanism, which clamps the jaws down using a ratcheting mechanism while still allowing wrist articulation, facilitating suturing tasks 4. Maestro has established parallel and inverse kinematic mappings. The only distinction between the two is that in the inverse mapping, the tendons connecting the wrist to the handle rotate 180° around the axis as they transition from the handle to the wrist 5. Maestro employs a unique symmetrical handle design that can rotate in the surgeon’s hand, generating axial rotation of the axis	1. Maestro’s notable features and advantages include a handle design that places a pivot point between the user’s fingers and thumb, making it the most compatible design with the da Vinci robot interface 2. A ratcheting locking mechanism is also included for suturing tasks to firmly grasp the needle without continuously squeezing the handle 3. Due to the symmetrical design of the handle, it can be gripped in various ways without affecting tool performance. It can also roll axially in the user’s hand to generate axial rotation at the distal actuator within the patient’s body without translation 4. A study exploring suturing at challenging angles indicated that compared to RealHand or traditional wristless manual laparoscopic tools, the Maestro design exhibited better user performance in achieving desired objectives	1. Future experiments will be needed to assess whether the device is easy to use in surgical procedures
DragonFlex (Delft University of Technology, Netherlands)	1. The wrist mechanism is rolling joint 2. The DragonFlex utilizes a handle control method to achieve parallel mapping 3. Rolling the distal actuator is accomplished by rolling the instrument in the hand, as described in the previous Maestro section 4. The published prototypes did not specify a locking mechanism 5. Two additional objectives of this design are to reduce joint clearance and cable slack, achieving high joint stiffness against external loads compared to underactuated bending wrist designs that bend under load, as described in the previous Maestro section	1. Notable features of the device include the aforementioned advantages of tolerance and rigidity 2. DragonFlex was intentionally developed with a minimalist design: the entire device comprises only seven structural components and four cables, facilitating straightforward assembly 3. The instrument is fabricated through additive manufacturing. This allows for cost-effective production in a disposable manner, which the authors assert is advantageous due to the challenging nature of disinfection for this design	1. The DragonFlex exhibits drawbacks such as protruding cables and joints. During rotation, as the bending angle increases, the internal cables tend to experience greater displacement from the instrument’s central axis 2. Additionally, with small gears, grooves, notches, and long, narrow bending cable channels, the instrument in its current shape is challenging to clean and disinfect 3. Given its involvement in medical device development, considerations for biocompatibility and sterilization need to be addressed
MiFlex (DEAM B.V. Inc., Netherlands)	1. The wrist mechanism is sliding joint 2. It features a pistol grip, a curved wrist design, and a 5-mm diameter shaft 3. The wrist articulation is facilitated by a thumb manipulation lever mounted on the handle 4. The wrist angle can be locked 5. There is also a ratchet mechanism to lock the end effector jaws 6. Axial rotation is achieved through a knob on the handle 7. The handle is reusable, but the end effector is disposable 8. Designed for inverse mapping	1. The instrument employs thumb control method utilizing a joystick. Research indicates that joystick control handles for finger manipulation are easier to use and less fatiguing compared to articulated handles like RealHand 2. In a comparative study between MiFlex and Laparo-Angle, it was found that there was no difference in surgical performance between thumb control and wrist control. However, participants expressed a strong preference for thumb control due to the tactile feedback during surgery	1. Future research should compare thumb-controlled instruments with other types of handle controls and hybrid controls, in addition to pistol grip and articulated wrist-joint instruments
Intuitool (University of Nebraska, NE, USA)	1. The wrist mechanism is sliding joint 2. This laparoscopic instrument is a prototype with a handle design that conforms to ergonomic principles 3. The device features a thumb trackball placed on the instrument handle to control the end effector, enabling articulation of up to 60 degrees 4. The opening and closing action of the end effector jaws are controlled by triggers on the handle, and can be locked via buttons on the handle 5. Designed for inverse mapping 6. It includes a knob for axial rotation 7. The design of Intuitool focuses on ergonomics and human factors, adhering to five user-centered design principles (easy to learn and use, efficiency of use, minimization of errors, subjective satisfaction, and adaptability), employing surgeon questionnaires and conducting user studies to create a comfortable, efficient instrument	1. Intuitool’s design emphasizes ergonomics 2. The instrument employs thumb control method utilizing a trackball. Studies have shown that manipulating the handle with finger operation is easier to use and less fatiguing compared to articulated handles like RealHand 3. A user study was conducted to assess the prototype. They found that 58% of participants believed Intuitool could alleviate hand/wrist pain caused by improper posture, while 53% felt the tool could reduce hand/wrist stiffness	1. The device remains at the prototype stage, or lacks research to prove its feasibility in surgery 2. Future research needs to compare thumb-controlled instruments with other types of handle controls and hybrid controls, in addition to pistol grips and articulated wrist-joint instruments
Easy Grasp (Tianjin University, China)	1. The wrist mechanism is rigid parallel joint 2. Easy Grasp employs a rod-driven mechanism, which offers the same robustness as the Radius instrument 3. The end effector jaws of Easy Grasp are driven by a push–pull rod mechanism, positioned outside the wrist articulation rather than integrated into the wrist 4. The instrument utilizes a handle control method with parallel kinematic mapping, providing ± 30° articulation around two axes 5. Axial rotation of the device tip is achieved by rotating the handle; the instrument shaft itself does not rotate, but the wrist and end effector jaws rotate within it 6. Easy Grasp features the capability for dual-handed use and the provision of an optional auxiliary handle for direct manipulation of the instrument shaft 7. The primary components of the prototype are made of stainless steel, except for the handle. The prototype has a diameter of 15 mm and weighs 331 g	1. Intuitive control and one-to-one mapping between the end effector and the operator are achieved 2. This instrument is the only one recommended for dual-handed use and is a reusable device 3. Experimental results validate that instruments designed in accordance with ergonomics are more dexterous than traditional instruments 4. Stitching and knotting experiments confirm the feasibility, structural integrity, and functional advantages of the instrument’s design	1. The end effector’s ± 30° articulation is lower than that of many other instruments, which may be a drawback 2. Despite the enhanced flexibility and intuitive control of the instrument, size and weight reduction improvements are still needed 3. For future work, additional performance experiments will be conducted to test its accuracy and dexterity, such as ring rod experiments, intracorporeal knot tying tasks, and suturing tasks using different types of needles and sutures
ArtiSential (Livsmed, Seongnam, Korea)	1. The wrist mechanism is sliding joint 2. ArtiSential is a pistol-grip instrument with a diameter of 8 mm 3. It features zero-radius bending; its wrist functionality is ensured by two articulations at the end effector, coupling their movements with those of the handle. The handle can move on both vertical and horizontal axes, transmitting its motion to the end effector 4. The handle is equipped with a jaw control ring, allowing surgeons to open and close the jaws using their thumb and index finger 5. Additionally, the end effector can be locked using a locking rod located on the handle 6. ArtiSential is disposable and comes in various forms distinct from the end effector type: needle holders, dissectors, graspers, monopolar hooks, and scalpels	1. ArtiSential is the first multi-DOF instrument with the broadest range of motion, with 360-degree articulation 2. A study indicates no significant differences in time spent per interval for completing suturing tasks between ArtiSential and the da Vinci robot. However, some surgeons may opt for ArtiSential due to its convenience, affordability, and independence from assistants 3. Unlike the da Vinci, ArtiSential allows surgeons to sense resistance from tissues or objects between the instrument jaws 4. ArtiSential can be more flexibly integrated alongside conventional instruments 5. Selective and temporary instrument usage may aid in anatomical maneuvers, such as the need for vertical traction during tasks like 11p or splenic hilar lymph node dissection	1. The dimensions of ArtiSential are larger than those of traditional rigid instruments, requiring excessive wrist twisting, which may lead to wrist stress. A study suggests that the wrist is more twisted when gripping the ArtiSential than with other devices 2. Another potential cause of wrist stress is the fulcrum effect, dependent on the distance to the target and the position of the trocar. Operating on targets farther from the working port may require wrist extension, while those closer may necessitate wrist flexion 3. A study indicates that ArtiSential did not improve surgical performance in laparoscopic cancer surgery. This may stem from the heterogeneity of surgical steps, including the type of gastrectomy and the extent of lymph node dissection. Hence, more robust research may be necessary to elucidate ArtiSential’s efficacy in cancer surgery

The target of developing articulated manual laparoscopic devices is to bring some flexibility benefits related to robotic surgery for patients and surgeons without having to bear the enormous financial costs of current surgical robots. However, at present, the research community has yet to reach a consensus on which factors make the articulated equipment easy to use. For example, the best direction of kinematic mapping, the best wrist joint design, how best to transmit axial rotation to the end effector, and whether a wrist locking mechanism is needed or optional [23].

Wrist mechanism design of multi-DOF

In recent decades, the realm of MIS has witnessed substantial progress, becoming a pivotal component of contemporary medical practice. The ongoing evolution of minimally invasive surgical instruments, particularly through the design and implementation of Multi-DOF laparoscopic surgical tools, with a spotlight on wrist mechanism innovation, has become critical in enhancing surgical accuracy and flexibility. This advancement not only drives surgical instruments towards higher efficiency and safety but also improves patient treatment outcomes.

The wrist mechanism, as an integral part of Multi-DOF surgical instruments, significantly influences the operation’s flexibility and precision. Its diverse and complex designs directly impact the adaptability and accuracy of surgical procedures. From rigid serial to parallel joints and onto flexible continuum designs, the exploration of various mechanisms aims to emulate human hand dexterity better, accommodating complex surgical scenarios and demands.

This section delves into the design principles, technical challenges, and recent advancements of wrist mechanisms in Multi-DOF surgical instruments. By categorizing and analyzing current designs, this examination evaluates the performance benefits and limitations of different wrist mechanisms and looks forward to future development trends. This aims to provide researchers and engineers with comprehensive technical references and innovative insights.

Wrist mechanism

The operational flexibility of surgical forceps is primarily determined by the wrist joint’s degrees of freedom. These degrees of freedom are categorized according to the motion patterns and structural characteristics of the wrist joint into three principal types: rigid serial joints, rigid parallel joints, and flexible continuums. Within the category of rigid serial joints, distinctions are drawn between rolling, sliding, and roll-sliding joints. Rolling involves the engagement of multiple points on one articulating surface with multiple corresponding points on another surface. Conversely, sliding is characterized by the contact between a single point on one articulating surface and multiple points on an opposing surface.

Rolling joint

A. Single-Degree-of-Freedom Rolling Joints: Single-degree-of-freedom rolling joints consist of multiple small joints in series or gear and rack engagements, relying on friction for motion transfer to achieve movement in a single plane.

During bending, the cables inside and outside the joint experience unequal tension due to different displacements. Han et al. [19] designed a wrist mechanism to address asymmetric cable displacement (Fig. 3a), allowing the driving cables to maintain equal tension in any bending direction. This wrist joint comprises seven stacked rolling discs (Fig. 3b) with wire displacement compensation, each disc having a diameter of 5 mm, resulting in a bending radius of approximately 6.5 mm and a bending angle of ± 90°. However, this simple stacked disc structure may lead to relative sliding at the connections, causing imprecise control.

Fig. 3.

Single-Degree-of-Freedom Rolling Joints. a 5 mm Rolling joints-based linkage end effector [19]. b Blueprint with dimension specification for a single disc [19]. c) Three-dimensional concept of the module used in the block mechanism [33]. d Concept of forces (blue) moving the block by pulling cables (red) [33] (Color figure online)

In minimally invasive surgery, the diameter of surgical instruments is a key factor affecting surgical quality. As the diameter of cable-driven surgical instruments decreases, the tension requirements for the cables increase, raising both manufacturing costs and difficulty. Enhancing joint rigidity can reduce reliance on high-tension cables. Kim et al. [33] proposed a blocking mechanism to improve the excessive deformation of traditional rolling joints. This mechanism, made of repeated unit joints consisting of upper and lower joints with a middle slider (Fig. 3c), mirrors the movement of traditional rolling joints while allowing the middle slider to move freely within a slot, sliding toward the side and experiencing tension (Fig. 3d). Experiments have demonstrated that, under the same external and tensile forces, the rigidity of the block mechanism increases by 140.4 to 353.9% compared to traditional rolling joints.

B. Dual-Degree-of-Freedom Rolling Joints: Dual-degree-of-freedom rolling joints offer more flexibility than single-degree ones, typically formed by orthogonally arranging multiple sets of single-degree rolling joints, enabling movement in two planes. Gear transmissions, characterized by high-precision, reliability, and stability, are often used to assist in bending movements of the wrist joint.

Wang et al. [34] and colleagues designed a wrist joint combining parallelogram and snake mechanisms. Neither is a continuum but consists of several unit joints in series. After insertion into the incision, the parallelogram mechanism extends to the vicinity of the lesion, followed by precise bending of the snake mechanism to reach the lesion. Both mechanisms are controlled by separate cables to prevent coupled movement. The authors also proposed a threading method to ensure cable length remains constant and evenly stressed during surgery, significantly enhancing the end effector’s flexibility. However, this complex threading method complicates manual assembly, potentially affecting the surgical forceps’ load capacity and control precision.

Kim et al. [35] developed surgical forceps for single-port laparoscopic surgery with a tendon-gear structure in the wrist joint (Fig. 4a), allowing the end to pitch and yaw. This structure replaces the pure rolling between traditional rolling joints with gear engagement, with each gear featuring two tunnel-like tendon sheaths for cable passage and motion transfer.

Fig. 4.

Dual-Degree-of-Freedom Rolling Joints. a Detail view of the distal joints of the articulated laparoscopic instrument that has two additional DOFs achieved from the tendon-gear mechanism [35]. b The system configuration of visible manipulator consists of a bendable end effector with multi-gear array mechanism and visualization unit, an actuation package with brushless DC-servomotors and Hall sensors, and a computer-based control unit [36]

Reducing the diameter of traditional surgical forceps necessitates using thinner drive cables, which have lower rigidity, leading to permanent cable lengthening and increased wear over time, ultimately resulting in motion lag. To address this, Wang et al. [36] designed a 9.5 mm diameter wrist joint with a multi-gear array mechanism (Fig. 4b), allowing multi-degree-of-freedom movements independent of cables while retaining the forceps’ pitch and yaw capabilities. A central channel reserved in the wrist joint’s center allows the installation of a visualization unit, providing real-time imaging during surgery. The wrist joint’s yawing range is − 76.8° to 76.2° with a load of no more than 250 g, and the pitching range is − 75.2° to 75.6° with a load of no more than 150 g. However, clearance and assembly errors in the gear mechanism can reduce the precision of surgical forceps. Contrary to rolling joints, sliding joints do not rely on friction for transmission; thus, less friction means smoother joint movement. Sliding joints typically revolve around a fixed axis or pin, making them generally resistant to lateral fracture.

Sliding joint

Compared to rolling joints, sliding joints operate independently of friction; thus, smoother joint movement is facilitated by reduced friction. Sliding joints typically revolve around a fixed axis or pin, rendering them resistant to lateral fractures [32].

A. Single-Degree-of-Freedom Sliding Joints: The EndoWrist, an end effector used in the da Vinci surgical robot, employs a combination of cables and pulleys to control two degrees of freedom at its tip, with pulleys winding the cables for motion transfer. Compared to other multi-degree-of-freedom surgical forceps, it can achieve a significantly smaller turning radius. However, after multiple tight-radius bends, the EndoWrist’s cables inevitably deform and fail, adversely affecting the forceps’ performance [37].

Zhang et al. [38] proposed a wrist joint based on a multi-slider linkage mechanism (Fig. 5a), employing rigid linkages for motion and force transfer. The basic mechanical structure typically includes three joints and two rotating connectors. Compared to the original multi-slider wrist joint designs [39, 40], this structure is simpler and more compact, achieving smooth bending motion while increasing the bending radius. In abdominal phantom experiments, two joints were able to rotate ± 35° and ± 55° consecutively, totaling a bending angle of ± 90°. However, this serial linkage and slider mechanism cannot integrate both pitching and yawing movements; achieving one requires changing the direction of the rotating shaft for the other motion.

Fig. 5.

Single-Degree-of-Freedom Sliding Joints. a The concept of the bending mechanism driven by sliding linkage, transforming the linear motion of link 1 to the rotation of frames 2 and 3 to realize ± 90 deg bending [38]. b Universal joint based-mechanism along with the central shaft system of the instrument [22]

To increase the reuse rate and reduce the costs of cable-driven surgical forceps, which require replacement after several sterilization cycles, Kumar et al. [22] designed a novel 7-degree-of-freedom laparoscopic surgical instrument. Its wrist joint comprises universal joints, crank-slider mechanisms, and four concentric sheaths, with the movements of the four concentric sheaths corresponding to four degrees of freedom (Fig. 5b): end effector rotation, overall forceps rotation, wrist joint yawing, and end effector grasping. Testing showed that the instrument’s maximum grasping force was 11.3 N, meeting the requirements for laparoscopic surgery and capable of being dismantled for sterilization and reuse.

B. Dual-Degree-of-Freedom Sliding Joints: The assembly of dual-degree-of-freedom sliding joints is similar to that of dual-degree-of-freedom rolling joints, typically formed by orthogonally arranging identical single-degree sliding joints.

Jin et al. [41] designed a flexible shaft composed of six microcard joints in series. The connection between the front and rear joints, as shown (Fig. 6a), involves the front joint being attached to the next via four set screws. Each micro universal joint can rotate 18° in two directions, allowing the surgical instrument to achieve a maximum bending angle of 108°. The flexible shaft is driven by four distributed cables to bend in any direction. Each micro universal joint is 18 mm long, making the total length of the flexible shaft 108 mm, offering flexibility and a broad range of motion. The use of many rigid linkages in the wrist joint can easily damage biological tissues during bending, and the complex structure poses sterilization challenges.

Fig. 6.

Dual-Degree-of-Freedom Sliding Joints. a Structure of the flexible shaft, connection of two joints and traction cords of the flexible shaft [41]. b Structure of the BCS joint and bending motion induced by the BCS joint [42]

To enhance the rigidity and precision of surgical instruments, ensuring that bending joints maintain a constant curvature under load and prevent torsional deformation, Ji et al. [42] designed ball-constrained spherical (BCS) joints (Fig. 6b). The wrist joint of the surgical forceps consists of 13 BCS joints in series. Each BCS joint comprises a spherical joint, ball bearings, springs, and spacers, with ball bearing guides on the spherical joint guiding the movement of the bearings to prevent torsional deformation of the wrist joint. Experiments demonstrated that within the margin of error, the BCS joints maintain a constant curvature under both unloaded and loaded conditions, supporting up to 5N of load without significant torsional deformation. The size of the ball bearings and springs significantly affects the diameter of the BCS joint, and a prototype built using PEEK resulted in a wrist joint diameter of 20 mm, failing to meet the requirements for current minimally invasive surgery.

Rigid parallel joint

Serial joints are characterized by their simplicity and high reliability and require multiple single joints in series to achieve multi-degree-of-freedom movements. This serial configuration accumulates motion chain errors and increases the surgical forceps’ turning radius due to the excessive number of joints. Parallel joints integrate the movements of pitching and yawing into a single parallel structure, thereby reducing the wrist’s turning radius. Additionally, parallel structures are known for their high-precision, rigidity, and load-bearing capacity and are primarily utilized in minimally invasive surgical robots. Various structures have been proposed, including 3-PUU parallel mechanism [43] (Fig. 7a), 2-PUU_2-PUS parallel mechanism [44] (Fig. 7b), 3-PU flexible parallel mechanism [45] (Fig. 7c), 3-PRS parallel mechanism [46] (Fig. 7d),3-PSR parallel mechanism [47] (Fig. 7e), 4DOF spherical parallel mechanism [48, 49] (Fig. 7f), magnetic spherical joints based on the linear Delta mechanism [50] (Fig. 7g), parallel mechanism of tripod structure [51] (Fig. 7h), and 3DOF origami parallel mechanism [52] (Fig. 7i).

Fig. 7.

Rigid parallel joints. a Schematic diagram of the proposed parallel manipulator (3-PUU) [43]. b Schematic diagram of 4-DOF parallel manipulator (2-PUU_2-PUS) [44]. c Schematic diagram of the parallel mechanism (3-PU) [45]. d Schematic diagram of the manipulator (3-PRS) [46]. e Kinematic structure of the wrist (3-PSR) [46]. f Schematic drawing of the manipulator (left) and the kinematic architecture of the wrist (right) [49]. g 3-DoFs positioning platform. The 2-DoFs rotational end effector is actuated by Bowden-cable, while the 3-DoFs positioning platform is actuated by flexible shaft [50]. h Tripod substructure of the parallel kinematics manipulator with three kinematic chains C1 to C3 [51]. i Three-DOF origami-enabled parallel platform [52]. j One module of DSD mechanism [53]. k Schematic representation of serial chains of 3-DOF wrist 3-RSR (left) and 3-PRR (right) [54]. l Overall structure of the wrist mechanism [55]

Ishii et al. [53] designed a Dual Spiral Drive (DSD) mechanism (Fig. 7j), where each linkage mechanism consists of two screws and a universal joint. The rotation of two linkage mechanisms enables the wrist to bend 90° in any direction. Furthermore, rotating the third linkage within the DSD mechanism allows for rotational movement of the end effector, while the end effector’s gripping and clamping movements are still achieved through cable driving.

Bazman et al. [54] developed a 3-degree-of-freedom wrist parallel mechanism (Fig. 7k), where the base of each RSR chain is connected to a PRR mechanism and rigid linkage, arranged symmetrically at 120 degrees apart. This wrist joint can achieve a bending angle of 90° in two directions. In 2022, building on the original 3RSR parallel mechanism, the team [55] added a central UUP linkage, forming a new parallel mechanism (3RSR-1UUR). The central UUP linkage, consisting of two universal joints (Fig. 7l), enables the wrist joint to translate movement through the linkage into the gripping motion of the end effector during turning. However, this parallel mechanism, when operational, expands outwardly with its three sets of linkage mechanisms, occupying considerable space and rendering it unsuitable for surgeries in confined spaces. Additionally, the exposed linkage components in the surgical environment are prone to contamination and clogging of structural gaps.

Soft continuum

In comparison to rigid serial and parallel mechanisms, soft continuums exhibit superior bending capabilities and flexibility, making them suitable for operation in winding and tortuous environments. The factors influencing the bending performance of flexible articulated joints include the dimensions and material of the bending section, the shape and orientation of the incisions, and the arrangement and spacing of these incisions. These elements determine the joint’s torsional stiffness, bending stiffness, and flexibility. By making incisions of different shapes on a complete hose, various bendable structures can be obtained.

A. Helical Incisions: Culmone et al. [56, 57] designed a fully 3D-printed surgical forceps featuring a 20 mm long omnidirectional steering segment. By removing unnecessary material along a helical line on the soft continuum, a structure capable of providing high torsional stiffness and low bending stiffness was created. As shown in (Fig. 8), the main shaft in the continuum ensures high torsional stiffness, while the T-shaped cross-section of the continuum is thinnest near the main shaft and thickest on the outer side. This design maintains low bending stiffness while restricting excessive bending angles of the soft continuum through its inherent structure. Two cables were used for steering, with a cross slot on the top for securing the wires. Song et al. [58] designed a structure comprising multiple helical segments and rigid segments (Fig. 9), where the helical structure not only maintains a constant curvature but also facilitates smooth bending of the wrist through uniform stress distribution. Unlike the design by Culmone C and colleagues, the authors did not retain a central shaft within the soft continuum. Instead, they utilized a hollow channel to carry surgical instruments, resulting in a structure with higher flexibility, elasticity, and resilience.

Fig. 8.

Steerable segment design. a Central backbone with four helicoids evenly placed around [57]. b Cross-section of the segments showing the T-shape of the helicoids, highlighted in red. Cables are shown in orange [57]. c Due to the T-shape, the helicoids touch each other at the inner curve of the segment, limiting the bending angle [57]. d Cross-section A-A shows the cable fixation point with the looped cables [57] (Color figure online)

Fig. 9.

The structure of the designed single-section flexible joint [58]

B. Symmetrical Incisions: Ryu et al. [59] developed a motorless-guided arthroscope surgical instrument. The wrist’s hose features equidistant symmetrical incisions on both sides (Fig. 10), each incision being rectangular. When the hose bends towards one side due to cable actuation, the rectangular incisions on the bending side deform into isosceles triangles. The bending angle of the wrist joint is determined by the number and spacing of the incisions, with the described wrist bending angle being ± 87.2°. Symmetrical incisions ensure the same stress and strain conditions when bending in either direction, but the length of the incisions limits the bending angle of each segment, allowing only left–right or up-down pivoting movements.

Fig. 10.

The geometry of the slit of the end effector and the angle of the end effector when the single slit is shrunk [59]

C. Asymmetrical Incisions: Swaney et al. [60] designed a wrist joint made from nickel-titanium alloy tubing with asymmetrical rectangular incisions, creating a flexible bending area driven by a single cable (Fig. 11). Compared to symmetrical incisions, the asymmetrical design reduces the number of driving cables required, saving design space and reducing the diameter of the surgical forceps.

Fig. 11.

The difference between a symmetric cutout design (left) and an asymmetric design (right) is shown. Note the significantly longer moment arm and reduced tendon force required to actuate the asymmetric design [60]

D. Orthogonally Arranged Incisions: Zhou et al. [61] designed a wrist structure made from PEEK material, cutting 12 orthogonally arranged symmetrical incisions on a 10 mm long soft continuum. A central channel with a diameter of 1.8 mm was reserved at the central axis for the driving cable. The pulling force of the driving cable causes axial compressive deformation to accumulate inside the wrist joint, becoming significant when bending exceeds 50°. To address this issue, their team [62] designed a new PEEK wrist joint structure in 2022 with enhanced axial stiffness. A polytetrafluoroethylene (PTFE) tube with a diameter of 2 mm and thickness of 0.5 mm was placed inside the central hole of the improved flexible wrist joint (Fig. 12). The PTFE tube, having a very low friction coefficient and being an excellent self-lubricating material, provides good bending performance while enhancing axial stiffness. Compared to previous designs, the wrist joint equipped with a PTFE tube showed a 57% increase in axial stiffness. The orthogonal arrangement of incisions allows for 2 degrees of freedom in movement but increases the number of cables used and complicates the winding method.

Fig. 12.

Design and structure of the improved flexible wrist joint [62]

Clinical application of multi-degree-of-freedom articular laparoscopic surgical instruments

Currently, Multi-DOF surgical instruments have attracted widespread attention from surgeons and researchers due to their high flexibility and cost-effectiveness. Particularly in gastrointestinal surgery, increased freedom of movement at the instrument tip aids surgeons in traction and exposure within narrow and deep anatomical spaces, facilitating tissue dissection or reconstruction and thereby enhancing surgical precision. The following section reviews the application of multi-DOF surgical instruments in gastrointestinal surgeries such as laparoscopic gastrectomy and colectomy, aiming to evaluate surgical outcomes, safety, technical feasibility, and their impact on postoperative recovery compared to traditional laparoscopic instruments and robotic systems under similar surgical conditions.

A prospective cohort study by Lee et al. [63] compared perioperative outcomes of laparoscopic gastrectomy using ALIs and robotic gastrectomy. The results indicated that laparoscopic gastrectomy with ALIs demonstrated comparable perioperative outcomes and shorter operative time compared to robotic gastrectomy. Lee et al. [64] conducted a retrospective analysis of patients undergoing laparoscopic gastrectomy for primary gastric adenocarcinoma. The study revealed comparable surgical duration, estimated blood loss, lymph node yield, and length of hospital stay between the conventional laparoscopic and ALIs groups. The ALIs group achieved a faster transition to a liquid diet. There was no statistically significant difference in early postoperative complication rates between the two groups. The novel laparoscopic articulating device, ArtiSential, was found to be a safe and feasible option without increasing operative time, hospital stay, or intraoperative bleeding. Using propensity score matching, Kang et al. [65] compared postoperative outcomes of a prospective patient cohort undergoing laparoscopic gastrectomy with articulating instruments to a historical patient cohort undergoing the same procedure with straight instruments, aiming to assess the feasibility of laparoscopic articulating instruments in gastrectomy. Compared to the traditional group, the ALIs group exhibited significantly reduced mean operative time and time to soft diet initiation but no significant differences in time to first flatus passage or total hospital stay. The ALIs group had a lower incidence of early postoperative complications, though the difference was insignificant. There were no mortalities in either group. The results suggest that the use of articulating instruments in laparoscopic gastrectomy is safe and does not increase postoperative morbidity. Their use may be associated with faster bowel recovery and fewer early complications. Kim et al. [66] evaluated the feasibility of a novel device in single-port laparoscopic distal gastrectomy (SP-LDG) for early gastric cancer (EGC) patients. The ArtiSential group showed no significant differences compared to the control group in terms of operative time, surgical quality, lymph node retrieval, length of hospital stay, or postoperative complications. The new multi-DOF articulating grasper proved to be feasible and could serve as an alternative to prehensile forceps in SP-LDG.

Jin et al. [67] presented a retrospective, single-institution, consecutive case study reporting the clinical experience of using ArtiSential for laparoscopic complete mesocolic excision (CME) with D3 lymph node dissection in patients with right-sided colon cancer for the first time. Short-term outcomes of patients undergoing laparoscopic CME combined with D3 lymph node dissection using ArtiSential (AG) versus traditional instruments (CG) were compared. The study indicated no significant differences in operative time, average estimated blood loss, or intraoperative and postoperative complications. However, AG demonstrated a higher lymph node yield and shorter hospital stay compared to CG. The results suggest that ArtiSential-assisted laparoscopic CME with D3 lymph node dissection for right-sided colon cancer is safe and technically feasible. Jin et al. [68] introduced a novel laparoscopic articulating instrument for laparoscopic right hemicolectomy. The ArtiSential instrument facilitates adequate traction and counter traction for surgeons with its intuitive movements. Its multidimensional freedom allows for broader surgical maneuvers compared to traditional laparoscopic instruments. The use of articulating laparoscopic instruments for laparoscopic right hemicolectomy is both safe and technically feasible. These instruments are ergonomic, enabling intuitive surgery, and are cost-effective compared to robotic systems.

Lee et al. [69] presented the latest clinical applications of articulating laparoscopic instruments (ArtiSential), demonstrating a standardized procedure for laparoscopic transverse colectomy using two ArtiSential instruments. The use of articulating laparoscopic instruments significantly aids in exposing the surgical plane and skeletonizing major feeding vessels. Performing laparoscopic transverse colectomy with articulating laparoscopic instruments is safe and technically feasible.

Darwich et al. [70] reported the initial single-center results of a series of low anterior resections performed using ArtiSential. Seventeen patients with mid-to-low rectal cancer participated in a pilot feasibility study to evaluate the role of ARTIESENTIAL articulating instruments in laparoscopic low anterior resection. Perioperative and short-term postoperative data were analyzed. The results indicated that ARTIESTIAL low anterior resection is both feasible and safe. All patients underwent successful TME surgery and achieved favourable oncological outcomes. A larger-scale study will now be conducted to assess the benefits of ARTIESTIAL compared to standard laparoscopic instruments. Darwich et al. [71] performed a low anterior resection on an obese male patient with lower rectal adenocarcinoma using ArtiSential full articulating laparoscopic instruments. After long-term neoadjuvant chemoradiotherapy with ArtiSential laparoscopic equipment, a laparoscopic anterior resection was performed. The complete articulation and multidimensional freedom provided by these instruments allowed for delicate and smooth dissection within the narrow pelvic cavity of this obese male patient. The patient was discharged on the 7th postoperative day. Pathology showed good TME quality with no lymph node involvement (0/15).

Jin et al. [72] demonstrated how to overcome internal collisions during single-incision laparoscopic appendectomy (SILA) and achieve good surgical visualization using a new articulating laparoscopic instrument. The results indicated that performing SILA using the new articulating laparoscopic instrument (ArtiSential) is safe and feasible. Additionally, it can be applied to various abdominal surgeries requiring a more excellent range of motion. Bea et al. [73] presented a technical report on the use of ArtiSential wrist articulating instruments for the treatment of perforated appendicitis with SPLS. They anticipated that this instrument could serve as a tool to ensure additional mobility for SPLS or for the treatment of diseases such as benign conditions, which are challenging to address with costly robotic systems. Furthermore, they believed that even for less experienced surgeons, familiarity with ArtiSential instruments would facilitate SPLS.

Darwich et al. [74] demonstrated for the first time using a fully articulating handheld ArtiSential disposable laparoscopic device for laparoscopic ventral mesh rectopexy (LVMR). There were no intraoperative complications. At 12-week follow-up, patients reported normal bowel function without needing laxatives or antidiarrheal. Clinical examination revealed no rectal prolapse or intussusception. The flexibility provided by this fully articulating ArtiSential instrument during LVMR suggests that performing the procedure using these instruments is feasible and safe. The dual-articulating end effector combined with traction-based mechanical devices achieves a unique operability not previously seen in the traditional laparoscopic field. Further research is evidently needed to elaborate on these observational findings. García-Jiménez et al. [75] presented the results of a prospective clinical series of 20 cases where FlexDex was tested for safety, efficacy, and ergonomics during intracorporeal suturing in laparoscopic surgery. Their findings indicate a safe and practical tool that enhances surgical ergonomics while providing controlled and precise manipulation. The device represents an alternative combining the precision and range of motion of robotic instruments. Van Der Vliet et al. [76] evaluated the safety and effectiveness of mechanical laparoscopic articulated needle drivers (LAND) (Flexdex) during implementation in a center of excellence for laparoscopic surgery and described its learning curve. Forty-five procedures (34 Roux-en-Y gastric bypass [of which 7 including diaphragmatic hernia repair], 2 diaphragmatic hernia repair with Nissen fundoplication, and 2 right-sided hemicolectomy) were included into this study. Results showed that LAND can be safely and effectively implemented in laparoscopic surgery at a superior center and is associated with a limited learning curve. Bibo et al. [77] illustrated a buttressed duct-to-mucosa anastomosis (modified Blumgart technique) during laparoscopic pancreaticoduodenectomy using an articulating needle holder (FlexDex). The FlexDex needle holder was successfully used to anastomose the pancreas to the intestine intraoperatively. Patients recovered from surgery without complications or postoperative pancreatic fistula. The results demonstrate the feasibility of using the articulating needle holder (FlexDex) for laparoscopic pancreaticoduodenal anastomosis. Hirano et al. [78] successfully treated esophageal achalasia and gastroesophageal reflux disease laparoscopically using the Radius Surgical System (RSS), including intracorporeal suturing. Results show that RSS may facilitate intracorporeal suturing and knotting in complex laparoscopic procedures.

Discussion

Although traditional laparoscopic surgery has been extensively applied in the field of gastrointestinal surgery, its technical, spatial, and visual limitations still need to be improved, coupled with a very steep learning curve. Straight, fixed-type instruments suffer from counterintuitive controls, poor ergonomics, and a limited range of motion, making processes such as tissue separation, hemostasis, and reconstruction particularly difficult [3, 79]. To some extent, the emergence of robotic surgery systems has addressed the limitations of traditional laparoscopic instruments by providing a broader range of motion for the end effectors, offering surgeons increased flexibility for more precise operations. Additionally, these systems enable more intuitive and comfortable operation, reducing surgical fatigue. However, in terms of cost-effectiveness, robotic surgery offers no advantages over traditional laparoscopy for most hospitals and patients. Furthermore, the absence of tactile feedback, which prevents the detection of tissue tension during surgery and can easily cause injury, the lack of long-term oncological equivalence data, and the limited number of uses are some of the drawbacks of robotic surgery systems. Therefore, research into developing multi-degree-of-freedom surgical instruments that offer similar flexibility to robotic systems at a lower cost by adding joint links to the actuator ends of traditional straight laparoscopic instruments has become a new focus.

The wrist mechanism, a key component of multi-DOF surgical instruments, is currently the subject of extensive research, including the use of cable-driven pulley systems [80–83] or multi-joint mechanisms [42, 84–86] to achieve multi-degree-of-freedom motion. However, these mechanisms are prone to issues such as joint gaps, cable slack, and motion lag, leading to cable fatigue breakage, low overall structural rigidity, large deformation, and reduced motion reliability. Moreover, multi-joint serial mechanisms can accumulate motion chain errors, resulting in poor precision and a large turning radius. Some scholars have begun exploring parallel structures to improve mechanism rigidity, load capacity, and reduce the turning radius [43, 46, 55, 87]. However, parallel structures involve many complex components, making it challenging to reduce the overall diameter size, unsuitable for handheld use, and difficult to achieve a closed kinematic solution. To avoid the problems associated with cable-driven mechanisms, some scholars have proposed non-cable-driven methods, such as gear systems, linkages, cams, or a combination thereof [22, 88–92], to achieve multi-degree-of-freedom motion in surgical instruments. Non-cable-driven mechanisms generally have greater rigidity, less deformation under load, and more accurate motion transmission, but they are more complex, making integration difficult. They may also have coupling issues between different degrees of freedom, affecting gripping stability. Additionally, friction and other interactions between mechanism parts can affect their transmission efficiency. Therefore, further research is needed to effectively combine these driving mechanisms to achieve a new type of transmission mechanism with high rigidity and precision, ample working space, and decoupled degrees of freedom.

Several mechanisms and companies have developed handheld multi-degree-of-freedom laparoscopic surgical instruments, with some products successfully commercialized. However, their clinical application is not widespread. A review of research on multi-degree-of-freedom surgical instruments reveals their safety, feasibility, and effectiveness to be comparable to, and in some aspects superior to, traditional laparoscopy. However, the research and use of these devices are still in the early stages. There is a lack of consensus in the academic community about the desired features of an ideal handheld multi-degree-of-freedom surgical instrument, such as the optimal direction of motion mapping, the best wrist joint design, how best to transmit axial rotation to the end effector, and whether a clamping or wrist locking device is necessary or optional [23]. Moreover, clinical research is scarce, necessitating larger sample size multicenter studies to further clarify the advantages of these surgical instruments.

Multi-degree-of-freedom surgical instruments, compared to traditional laparoscopic instruments, will be easier to use, offering surgeons comfortable and precise operation, reducing fatigue, and lowering the difficulty of surgery. Research into high-precision, high rigidity wrist mechanism design and the development of safe, applicable, low-cost, high-precision multi-degree-of-freedom laparoscopic surgical instruments will enable surgeons to perform delicate operations in various anatomical areas (especially in narrow, deep spaces), such as tumour excision, lymph node dissection, and tissue reconstruction, bringing better surgical outcomes for patients, including safer resection margins, less blood loss, and shorter operation times. This represents a research field with both social and economic benefits.

Author contributions

All authors contributed to the study’s conception and design. Shibin Yang proposed the idea of the article. Jianhao Jiang and Jingyun Huang performed literature search and data analysis. Yisi Tu wrote the first draft of the manuscript. Shibin Yang and Jianbo Sui critically revised the work. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

This research was sponsored by the Natural Science Foundation of Guangdong Province [Grant Number 2023A1515012634], the Science and Technology Program of Guangzhou, China [Grant Number 202206010104], and the National Natural Science Foundation of China [Grant Number 52175386].

Declarations

Disclosures

Yisi Tu, Jianhao Jiang, Jingyun Huang, Jianbo Sui, Shibin Yang have no conflicts of interest or financial ties to disclose.

Research involving human and animals participants

This article does not contain any studies with human and/or animal’s participants performed by any of the authors.