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An MD&DI July 1998 Column

Manufacturers are vying for a bigger slice of the minimally invasive surgery market.

When laparoscopic cholocystectomy (or "lap-choly," as it came to be known) was introduced nearly a decade ago, many believed the era of open surgery had come to a close. But in fact, the market for minimally invasive surgery (MIS) never seemed to realize its full potential, and after an initial boom, it leveled off considerably.

Fewer procedures were converted to MIS than originally expected, primarily because of the complexity involved. In the world of MIS, the lap-choly is a relatively simple procedure, requiring the surgeon to identify, grasp, cut, and cauterize tissue. Most other procedures are not so cut-and-dried but involve delicate suturing or maneuvering around organs into tight spaces. Many surgeons simply lacked the necessary skills—and the unwieldy instruments didn't help. Others found the idea of observing the procedure on a monitor counterintuitive. If outcomes were not significantly improved, surgeons said, a minimally invasive approach simply wasn't worth the effort.

The Octopus tissue stabilization system uses suction cups to steady the heart and provide surgeons with anterior and posterior access. Photo courtesy of Medtronic (Minneapolis)

But all that is changing. Even if cost, outcomes, and surgical ease were equal, one major factor would continue to drive MIS technology over conventional open techniques: patient demand. With reduced hospitalization and postoperative pain at stake, more patients are specifically looking for surgeons with MIS experience. As a result, hospitals are beginning to feel they can't afford not to offer MIS—particularly in the cardiac market, which holds high stakes for patients and hospitals alike. Patients are understandably drawn to a procedure that doesn't require a full sternotomy, while hospitals want to be seen as leaders in treating cardiac disease. In the United States alone, more than 300,000 coronary artery bypass graft (CABG) procedures are performed each year.

A HEART-STOPPING PROCEDURE

The medical community is still debating which is more of a liability in traditional CABG—the sternotomy or the heart-lung machine. As a result, companies such as Medtronic (Minneapolis), U.S. Surgical Corp. (Norwalk, CT), Heartport (Redwood City, CA), Guidant (Menlo Park, CA), and Cardiothoracic Systems (CTS; Cupertino, CA) have developed a range of approaches covering every permutation of stopped and beating heart techniques with and without cardiopulmonary bypass and partial or no sternotomy.

U.S. Surgical was one of the pioneers in the field, announcing as early as 1995 the first successful minimally invasive direct coronary artery bypass (MIDCAB), performed in France, using the company's instruments. The latest approach to MIDCAB requires a retractor to separate the fourth and fifth ribs above the heart to maximize the access portal. A stabilizer in the shape of a dinner fork with the inner tines removed presses down on the heart to keep it steady enough for anastomosis. (Reportedly, the first stabilizers were dinner forks!) Of the procedures that require a heart-lung machine, some connect to it through the groin, while others connect to it through the chest incision.

U.S. Surgical recently unveiled its latest offering, the Mini-CABG access set. The retractors and stabilizer are attached to a plastic ring, and the whole system holds itself in place around the incision. The ring also organizes the sutures that the surgeon might use to pull back the pericardium. Simplicity of design and extensive use of molded plastic give the disposable instrument a solid price advantage; the complete set of instruments runs less than $500—significantly less than competing disposable systems from CTS and Heartport. CTS recently introduced its third-generation stabilizer, the AccessPlus. Heartport's EndoCPB system is not designed for use on a beating heart but rather involves stopping the heart and draining it of blood, as in the conventional open procedure. The heart-lung machine is connected to the patient via a single femoral incision.

Harvesting the saphenous vein, commonly used in bypass procedures (Guidant; Menlo Park, CA).

Despite recent advances, minimally invasive CABG still presents a number of difficulties for the physician. Manipulation is perhaps the most important challenge, because surgeons still have trouble getting at vessels behind the heart. Also, a beating heart twists, and the tissue beneath the fork-type stabilizers can migrate, further complicating the precise task of grafting vessels 1–2 mm in diameter. The Heartport system obviates these concerns because a stopped heart is easier to manipulate and doesn't move on its own; but of course, it also requires the expensive heart-lung machine. With forked stabilizers, some surgeons actually suture the heart to the tines to prevent unwanted movement. Medtronic's Octopus tissue stabilization system takes this one step further. The device actually grasps the heart via suction cups on the end of two fully articulating arms (hence the name). "One of the major features of the Octopus," says Ann Scott, marketing manager for Medtronic's minimally invasive cardiac surgery division, "is that you can access vessels on the anterior and posterior sides of the heart. If you're going in with a fork that uses downward pressure, and you've got to graft on the back of the heart, imagine how hard it is."

SEWING AND HARVESTING

Even with a steady working area, suturing remains difficult, and any manufacturer that can simplify the process stands to gain significant market share. Albert Chin, MD, founder of Origin Medsystems (now part of Guidant), explains, "When you're trying to sew two small vessels together and you have a beating heart, you need to be able to do that quickly. So we're looking at ways to do that faster." Scott at Medtronic agrees, noting that a typical graft will take approximately 12–18 sutures. "So with a quadruple bypass," she says, "you're going to be doing a lot of sewing." Medtronic has developed an intravascular arteriotomy cannula to simplify the task. The device is inserted into the coronary artery just prior to grafting to allow continuous flow while the surgeon completes the anastomosis.

The MIDCAB boom has fostered a demand for ancillary and assisting devices as well—particularly for devices that harvest vessels to use as grafts. The basic CTS system, for example, includes the Access MP lift used in harvesting the internal mammary artery (IMA); it lifts tissue and spreads the incision to provide a wide view of the operative field. Also recommended for use in IMA takedown, Medtronic's ClearCut 2 electrosurgical handpiece combines a cutter, coagulator, and light in a single device. Completely endoscopic IMA takedown, as part of a completely endoscopic cardiac procedure, will probably attract more research dollars in the near future.

Other manufacturers have been developing less-invasive ways of harvesting the saphenous vein from the leg, which is perhaps the most commonly used bypass vessel. Origin has developed a technique that uses a transparent tapered tip and a balloon—much like an angioplasty balloon, but much bigger—to form a tunnel along the vein that is then filled with CO2 to create a working cavity. The vein can be separated from the surrounding tissue and removed intact. The traditional method requires an incision that usually extends from the patient's groin to ankle. With the VasoView, says Chin, "We're able to take the whole vein out sometimes with only one incision in the knee."

As with the actual bypass, the less-invasive technique is trickier, but far less traumatic, and patient demand will undoubtedly fuel robust market growth. "For example," says Chin, "a center in Amsterdam that started using this technique had to separate patients after surgery into two separate ICUs, because one guy would wake up and see his leg fileted open, and the guy next to him would have just a small incision, and the first patient would complain so much to the surgeon." The same technique, he says, can also be used for peripheral bypass, where a minimal incision is "even more important because the reason these people are having the operation in the first place is that they don't have enough blood flow to the extremities." Origin is not the only manufacturer to introduce an endoscopic vein harvester. Ethicon Endo-Surgery (Cincinnati) also has a system comprising a vessel dissector, subcutaneous dissector, subcutaneous retractor, and clip applier. The disposable devices, molded predominantly from Dow Plastics' Calibre polycarbonate and Isoplast polyurethane, collectively sell for about $400 to $700.

RETHINKING LAPAROSCOPY

The relative success of cardiac MIS has prompted many device designers to reconsider current laparoscopic techniques with an eye toward increasing operational ease and converting procedures that have resisted a minimally invasive approach. In some cases, this entails finding a way around the need for insufflation. Chin and his colleagues, for example, have developed a simpler MIS approach to treating abdominal aortic aneurysm. Current techniques are hindered by the lack of direct access to the aorta. Traditional surgery entails a major abdominal incision and removal of the intestines, and even a laparoscopic approach through the belly requires retraction of the bowel. Chin's new technique gains access through the flank with the help of a device called the Laparolift, which mechanically retracts the abdominal wall to provide a working space in which to attach a standard bifurcated graft.

Gasless laparoscopy, Chin says, is inherently simpler. With pressurized CO2, instruments can only be inserted through a trocar and therefore have to be longer and thinner. "That makes it hard for things that are more difficult, like sewing." Another advantage to the flank approach is that it can be used for spinal procedures, which also hold great potential. Approximately 400,000 lumbar discectomies, for example, are performed worldwide each year. Past attempts to remove herniated discs endoscopically failed to achieve expected results, but new approaches such as Chin's promise to perform much better. Sofamor Danek (Memphis) is another company pursuing this market through its microendoscopic discectomy (MED) system. The MED system reportedly allows the surgeon to see more of the target area than is possible through the traditional open technique.

It may be some while before gasless laparoscopy becomes the standard. In the meantime, manufacturers are taking advantage of recent advances in materials and manufacturing processes to create devices with greater dexterity. Pivotal Medical Innovations (Whittier, CA), for instance, has developed a 5-mm-diam laparoscopic instrument with an articulating tip. The instrument is equipped with end effector blades that pivot 110° and rotate 360°, capabilities that have eluded designers for years. "In making a relatively complicated mechanism small," explains John Stiggelbout, Pivotal's director of R&D, "you encounter two problems." The first is backlash or looseness in the instrument. "That has to do with manufacturing tolerances. It's a percentage of the sizes you're working with," he says. Large parts can tolerate minuscule deviations from spec, but miniature parts can't. "If you've got a part that's ten thousandths of an inch in diameter and you've got a ten thousandths of an inch flaw, it's not going to work," he says.

Blades that pivot and rotate enhance a miniaturized device's capabilities (Pivotal Medical Innovations; Whittier, CA).

The second problem deals with part stress. "To make an instrument work, you need to be able to exert a certain amount of force, as between cutting tips for scissors," he explains. "When you miniaturize things, you still need to maintain that force, but there's much less material to carry that load, so part stresses go up." Stiggelbout's designers commonly work with stainless-steel alloys with yield strength between 160 and 170 kpsi. "A decade ago, you couldn't do that," he says. Such small functional parts also wouldn't be feasible without CAD and solid modeling to predict part stress. Improvements in metal forming help too; Stiggelbout estimates that about two-thirds of his manufacturing needs are met by wire-cut electrodischarge machining. Pivotal is also developing a 3-mm version of its instrument, which would be used in spinal discectomies, among other procedures.

Ranjan Mukherjee, PhD, of Michigan State University, echoes many of the concerns voiced by Stiggelbout. Mukherjee has developed a laparoscopic instrument for enhanced dexterity in MIS. The instrument has a segment that can articulate up to 180°—"like a finger, only bidirectionally," he says. The instrument tip can rotate unrestricted about the longitudinal axis and can open and close for grasping or scissoring. "The articulation allows the instrument to approach tissue at an arbitrary angle while the tip rotation enables suturing, which is the most difficult task in minimally invasive surgery," he says. A prototype, which can pass through a 10-mm trocar, is currently under construction and will be able to apply forces up to 1 lb in magnitude at the surgical site. "Considering the size of the instrument and its kinematic structure," he notes, "a 1-lb force is significant."

The difficulty in the design of such an instrument, according to Mukherjee, can be attributed to the conflicting requirements of small size, good dexterity, fast response, high repeatability, low backlash, and low force magnification. "The force magnification stems from the kinematic structure for articulation and limits the maximum force that can be applied at the surgical site," he explains. This, along with the dexterity requirements and space constraints, requires an innovative mechanical design to transmit motion from the base to the tip of the instrument. Unfortunately, repeatability and high-bandwidth requirements preclude the use of superelastic alloys for motion transmission and shape-memory alloys for actuation. "Shape-memory alloys are easy to heat, but their cooling may take long—more so because they would be inside the instrument where heat convection would be low," he says.

ANASTOMOTIC ROBOTICS

Mukherjee envisions the instrument as part of a robotic system, or more specifically, as the slave component of a computer-controlled master-slave system. "In this setup," he explains, "the surgeon will be involved at the supervisory level. He will move his arm holding the master. His motions will be picked up by the computer and translated into appropriate slave movements. This setup will allow the surgeon to perform dexterous and fine motions at the surgical site through an ergonomic interface." Mukherjee would also like to integrate his device with a camera. "We are thinking in the long run that as the instrument bends behind organs, the camera should bend with it to provide the surgeon a view from the direction he would like to see it." As it turns out, the computerized scenario he envisions is already nearing commercialization, and the imaging technique might not be far behind.

Medtronic has entered into strategic partnerships with companies in each of these fields, namely, Computer Motion, Inc. (Goleta, CA), and Vista (Carlsbad, CA). Computer Motion has developed a computerized robotic system, known as Zeus, for minimally invasive cardiac surgery.

Robotic assistance is attractive for several reasons. For example, many surgeons find MIS difficult because instrument manipulation is counterintuitive. To move an instrument tip from left to right, the surgeon actually moves the handle from right to left. A clockwise circle, on the other hand, is still made by moving the handle clockwise, although the tip starts and stops 180° from where the handle ends up. In addition, the long, thin shape of the devices amplifies hand tremors and other unwanted movements. A robotic arm obviates these problems, enabling surgeons to operate as they would in an open procedure, by translating their motions and scaling them down to the microsurgical level.

The Zeus system has three basic components, explains Anja Schmelter, marketing manager for Medtronic's minimally invasive cardiac surgery division. The first is an assembly of three robotic arms that attach to the operating table and hold an endoscope and two surgical instruments. The other components are the computerized controller and the surgeon console, where the surgeon sits—somewhat at a distance from the patient—manipulating a set of handles that resemble conventional surgical instruments. The computer interface scales and filters the surgeon's hand movements, translating the motions to the corresponding instruments inside the patient's body. "Zeus will allow the surgeon to do precise micromanipulation that would be very difficult to do with his own hands," she explains.

Computer Motion's system is not the only one nearing release. Intuitive Surgical (Mountain View, CA) is also developing a robotic device. As with other instruments, advances in manufacturing techniques have only recently made such a system possible. Intuitive's computer, for example, employs four digital signal processors that provide 100 times as much processing power as was possible just three years ago.

A NEW LOOK IN HEADGEAR

In the area of imaging, Medtronic has also partnered with Vista Medical Technologies (Carlsbad, CA), bundling the company's Series 8000 head-mounted display and information system as part of its suite of cardiac surgery tools. Rather than watching the procedure on a monitor, the surgeon sees it—along with diagnostic and monitoring data—right in front of his eyes. "The advantage of Vista is that it's a 3-D system," explains Medtronic's Schmelter, "so it provides the depth perception that you couldn't get with other systems." A completely endoscopic cardiac procedure may be a long time away, but cardiothoracic surgeons are already finding ways to work video imaging into their procedures—for example, in assisting endoscopic IMA harvesting and mitral valve repair and replacement through small incisions.

Vista's technology was transferred from the aerospace industry, where it was used by fighter pilots. According to Allen Newman, vice president and general manager of Vista's head, neck, and spine microsurgery division, the company worried that the technology might be difficult for surgeons to accept. "As it turned out, it was the easiest thing, because the human factors were so natural."

Vista also has an arrangement with Sofamor Danek to distribute its StereoSite visualization and information system. The voice-actuated head-mounted display can integrate several image sources, including 3-D microscopes, navigation systems, endoscopes, and ultrasound. The full-color LCDs can present primary and secondary images simultaneously. "In traditional microsurgery," Newman explains, "the surgeon's eyes are glued to the microscope. But then he has to look up at a CAT scan or MRI or walk away to an x-ray board or a navigational system. Now, instead of having to look at a monitor, all that information can be integrated into the headset display." Vista has also developed related products, such as a fully sterilizable miniature 3-D camera for abdominal and thoracic MIS that could hasten the introduction of telerobotic surgery.

Still, not everyone is excited by the prospect of an MIS robot. "That's a very technologically advanced device that certainly will enable surgeons to do any type of surgery," says Origin's Chin, adding, "It also could bring a very hefty price tag—about half a million dollars. I tend to look at something in the middle, a mechanical assistant for surgeons to do a certain technique such as sewing but staying short of full robotic. That's got more promise. Healthcare costs are in the forefront of everybody's mind, so we have to be able to come up with technology that's cost-effective—simpler instruments that are still innovative enough that give a boost to the surgeon's skill."

CONCLUSION

Nonetheless, telerobotic surgery seems to be the next step for an industry that has come a long way in a very short time. "I think the outlook for the industry is finally turning around," says Newman. "The technology is becoming cost-effective and is going to give physicians greater therapeutic capabilities, which will in turn allow better outcomes. Microminimally invasive cardiovascular and spinal surgery—these were all limited by technology. But now, the technology is coming around to meet those demands." Mukherjee is equally optimistic, adding, "I see MIS expanding its horizons, going into areas where it has not gone before." Medtronic's Schmelter sums up the prevailing philosophy in current MIS research. "Ten years ago, only a few pioneers were doing surgery on a beating heart—and look where we are today."


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