Chapter 12:
Microsurgical Equipment and Instrumentation

Bruce R. Gilbert, M.D.,Ph.D.
Clinical Assistant Professor of Surgery (Urology)
in SURGERY OF MALE INFERTILITY
edited by Marc Goldstein,M.D.


I - Introduction

Microsurgical instrumentation extends the surgeon's ability to handle small structures atraumatically and to allow precise alignment of these structures. Therefore, microsurgical equipment and instrumentation has always been a compromise between the engineer's ability to satisfy the surgeon's needs and the availability of technology to accomplish this goal. It was in 1922, that Dr. Nylen of the University of Stockholm first used a low powered monocular microscope for surgery. The addition of a slit lamp with an added light source and a support stand created the first binocular operating microscope. Naturally this microscope was cumbersome and difficult to use, and for the next 3 decades surgeon's continued to use magnifying spectacles and loupes. It was not until the 1950's that engineering advancements allowed introduction of a surgical microscope. The first operating microscopes provided coaxial illumination, stereo observation, focusing and magnification changes at one working distance. They also provided a stable and maneuverable suspension over the surgical field. These advancements brought about the rapid spread of the surgical microscope from Otology into other medical disciplines, including Ophthalmology, Neurosurgery as well as plastic and reconstructive surgery. These advancements also resulted in the development of an operating microscope that provided a wide, stable and brightly illuminated field for microsurgery (Figure 1).

In 1964, Ota performed the first successful extracorporeal repair of renal vessels with the assistance of an operating microscope. Since that time, urologic applications of microsurgery have included ureteral anastomoses, hypospadias repair, penile revascularization, penile venous ligation, testicular autotransplantation, microsurgical varicocele ligation, vasotomy/vasogram, vasovasostomy and vasoepididymostomy together with creation of alloplastic spermatoceles and epididymal sperm aspiration(1). With improvement in optical magnification, has come the need for the development of instruments that differ markedly from those used by traditional surgeons. These instruments must be produced with precise tolerances and be able to transduce the relatively gross movements of the operating surgeon into the smooth, well-defined and precise control as viewed through the operating microscope. This has also required development of suture material and needles capable of atraumatically approximating tissues.
In this chapter, we discuss microsurgical equipment and instrumentation, beginning with an overview of the basic physics of optical magnification and then discussing the state-of-the-art in loupes, operating microscopes and documentation systems. This will be followed by an overview of microsurgical instrumentation and the microsurgical suture material available today.

II Optical Magnification and Documentation Systems

A. The optical advantage - Physics/Physiology of optical magnification.

For any microsurgical application the optical magnification system must provide:
1. enlarged upright and non-reversed images of the operating field;
2. undistorted three dimensional images with good contrast and high resolution;
3. sufficient working distance between the surgical field and the microscope body for the surgeon to work comfortably;
4. true color reproduction for precise detail recognition;
5. homogenous reflection free illumination;
6. ease of rotation around the axis of observation;

The basic components of the optical system of an operating microscope are shown in Figure 2. This consists of the front lens or objective, a magnification changer, the binocular tubes and eyepieces and the illumination source.

1. The objective lens - normally used in microsurgery, has a focal length ("f"), which ranges from 150-400 mm usually in steps of 25mm. This distance is identical to the working distance (the distance from the objective lens to the surgical field). The choice of the working distance oftentimes relates to the height and build of the surgeon, as well as the size of the microscope and design of the binocular tube. If the working distance is too short, the surgeon has difficult manipulating instruments between the operating field and the objective, a longer working distance forces the surgeon to tilt the microscope or to work in an awkward position.

2. The magnification changer - Surgical microscopes are usually equipped with one of two different types of magnification changers(2). The first, which is the stepped or manual system, is based on the Galilean telescope. The Galilean system consists of a convergent objective and a divergent eyepiece aligned in opposition to each other.

In a three step system, one Galilean telescope system, (two lenses), is placed in the path of the observation beam on a cylinder or turret. In order to change the magnification factor, this cylinder rotates, changing the relative position of the two lenses. A free passage position, (no lenses), with a magnification factor of 1 is located between the lenses. Thus, this system provides two magnification factors plus the free passage position, the "three steps". The five step magnification changer includes an additional telescope system and two more sets of lenses, providing four magnification factors and one free passage position.

The motorized or zoom system allows a continuous change of magnification without any blackout. Two motorized lens systems move simultaneously along a linear path that coincides with the optical beams and paths. The relative position of the lenses in the linear path determines the magnification factor. The range of magnification factors from highest to lowest depends on the microscope type and is either 1:4 or 1:5.

The advantage of the step system is that is requires a minimum of space and thus permits the overall height of the microscope to be kept small, and in turn, allows the working distance to be maximized. The motorized zoom system has a major disadvantage that as the zoom range increases, the construction height of the instrument also increases, therefore decreasing the useable working distance.

3. Binocular tubes consist of a lens and prism system in each observation beam path. The lens accepts the image from the magnification changer, and the prism shifts the image to make it upright in order to accommodate the observer's own eyes. Binocular tubes have focal lengths, ("f"), because the lens of the tube acts like the objective in a telescope. Wide field binocular tubes have a focal length of 170 mm (f=170). Binocular tubes are straight, inclined or not inclinable. Straight tubes are parallel to the microscope access and are used in procedures where the microscope body is tilted, such as ear surgery. Inclined tubes are set at a 45 degree fixed angle to the axis of the microscope and are used when the microscope remains in a vertical position, such as most urologic procedures. Inclinable tubes are adjustable to any angle to the microscope axis and are useful where freedom in positioning is a requirement.

4. Eyepieces - eyepieces magnify the image from the binocular tube lens and determine the size of the field of view (by means of a field stop). Magnification factor and the size of the field stop in millimeters is engraved on all wide angle eyepieces. Eyepieces provide diopter adjustment so that eye glass wearers can correct for refractive errors and work without glasses. In addition, most manufacturers of operating microscopes provide an optical design whereby the distance between the eyepiece and eyes is greater than 20 mm. This is termed a high-eyepoint eyepiece (Figure 3). High-eyepoint eyepieces can be used by eyeglass wearers, without any decrease in the field of view.

5. Magnification size of the field of view, illumination of the object, depth of field - Magnification can be calculated by the formula given below, where fb=focal length of the binocular tube fo=focal length of the objective, me=magnification of the eyepiece, mf=magnification factor of the magnification changer.

Total magnification = M= { ( fb / fo ) x me } x mf

for example, with 10x eyepieces, binoculars of 170mm, an objective lens of f=200mm and a magnification factor of 1.2, the total magnification would be:

Total magnification =M= { (170mm/200mm) x 10 } x 1.2 = 10.2 x
For wide field eyepieces the field of view (Fview) is given by the formulas:
(Fview) = 220/M
The ratio between the focal length of the binocular tube and the focal length of the objective, not only determines the working distance and the total magnification as given above, but also the size of the field of view, the illumination of the object and the depth of field. The greater the focal length of the objective, the smaller the magnification M and thus the greater will be both the visual field and depth of field. However, the magnification obtainable and the illumination of the object will be decreased. Conversely, the shorter the focal length of the objective, the greater the magnification and thus the smaller will be the both the available visual field and depth of field, however, there will be a greater maximum magnification obtainable. Illumination in the object however, decreases with magnification.

Lighting of the surgical field is an issue that involves both technical as well as physiologic problems(3). Both of these problems are related to the size of the operating field that needs to be illuminated together with the heat produced by the illuminating source. The larger the size and the brighter the operating field, the greater the intensity of the light source that is required and therefore the greater the heat that needs to be dissipated. Placement of this power source near the operating field, would require a ventilation system that would interfere with sterility in the operating room. Therefore, fiberoptic cables have been employed to deliver illumination to the operative field from a distant light projector. Even this solution though is not perfect. This "cold light," is actually only slightly cooler than the same quantity of directly transmitted light and therefore, attention needs to be directed towards heating of tissue and it's drying out. Attempts to replace glass fibers by fluid conductors have not yet been able to eliminate this problem. Repeated irrigation is advisable in these cases.

Dual headed microscope - In order to have an assistant help during an operation, it is necessary to provide another binocular tube for use by the assistant for "face-to-face" urologic procedures. These are usually positioned 180 degrees apart from each other, and through the use of an optical beam splitter, allow use of both binocular tubes simultaneously, permitting both surgeons to see the object in equal stereopsis and with equal brightness and equal magnification.

Lasers and microsurgery - The precision of a surgical laser can only be fully exploited if precise microscopic alignment exists. The physical link between the two is a micromanipulator. The micromanipulator is physically attached to the microscope and thorough a series of focusing lenses is steered to the target tissue by an integrated mirror that the surgeon controls with a hand control ('joystick'). Laser precision is made possible by synchronous focus (termed parfocality), between the laser beam and image path of the microscope. Optimal performance requires that the microscope be accurately focused on the surgical field and that the focal distance of the microscope image beam and laser beam be equal.

B. Magnifying spectacles (loops)
, provides the operating surgeon a simple and less expensive means of taking advantage of optical magnification. There are two basic optical systems that are employed, one being the Galilei system and the other the Kepler system(3).

The Galilei system incorporates both a positive and negative lens. The total thickness of the construction can be kept relatively thin and an upright and laterally correct image is produced. However, the major disadvantage is that the visual field is a function of the front lens which must be made increasingly larger to provide an adequate field of view. This then incurs both weight and space problems and magnification is limited to 2.5 to 3 times. Above this magnification factor, the spectacles become too thick and heavy and the working distance too small. These are usually the least expensive of magnifying spectacles.

The Kepler system employs two positive lenses and since the image is therefore inverted in the process, optical inversion is necessary. This system is commonly used in prismatic binoculars that use a complex system of roof prisms. However, for spectacles these would be too large to be usable. Instead, direct vision prisms are employed. Again, as in the Galilei system, magnification is limited by the size constraints of the loops and with the Kepler system, depth of field is small and therefore requires steadiness of the neck during lengthy operations resulting in rapid fatigue.

Loops also do not provide a way of changing magnification, nor the ability to photo-video the microsurgical procedure. In addition, due to size and weight constraints, are limited to magnification of 2-8 times, however they do provide a relatively inexpensive means of optical magnification.

Still and Video Documentation Systems
Documentation of microsurgical procedures has become commonplace. Most optical instrumentation has incorporated fittings to add either a still (usually 35mm) format or video (usually VHS or super VHS) capabilities. There are several considerations that will insure effortless and unobtrusive documentation. Due to cost considerations these are often a "wish list" rather then requirements. Control of the camera should be available to the surgeon as well as an assistant. Foot controls for recording and "instant replay" are desirable. The camera must be "par focal" as discussed earlier. Repeated visual checks while recording insures "in focus" images. The availability of an automatic adjustment to insure par focality would be a great time saver. Usually additional lighting is required in part due to the beam splitter needed to divert the image to both the optical recorder as well as the eyepieces. Therefore, irrigation of the field should be done frequently to prevent drying of the tissue.

Microsurgical suture materials:
Microsurgical sutures are composed of a needle (Figure 4 and Figure 5) and suture strand. The needles used for vasal anastomoses have been designed to accommodate the specific requirements at each level of the anastomosis. For the inner mucosal alignment a double armed 2.5cm suture is used. The point has precision cutting edges to facilitate penetration of the tough muscularis layers without undo drag. The blade which is the transition between the needle point and is designed to minimized tenting of the tissues. The body is bi-curved (950/1070) and 70 microns in diameter. The bi-curved needle simplifies inside-out placement of sutures while providing short, deep bites and immediate exit which reduces the risk of backwall involvement. The needle is then swaged to a black monofilament 10-0 suture strand (Sharpoint AA-2492, Ethicon D6890). The suture we use for the seromuscular and adventitial layer a single strand 9-0 black monofilament suture strand (5-6 cm in length; Sharpoint AA-1825, Ethicon Vas100-4) is swaged to a 100 micron vas cutting needle(4) (Figure 6).

Microsurgical instrumentation
The choice of instruments used for microsurgery is as critical as the experience of the microsurgeon. These instruments are often controlled by a rolling movement provided by pressure applied between the distal phalanges of the thumb and second or third fingers. Therefore, the surfaces of these should be designed to prevent slip. The instrument itself should be made of a non-glare material and should provide precise control over closure of the perfectly aligned tips. General specifications of each of these instruments will be presented here, while more specific recommendations will be presented in later chapters.

Grasping/Dissecting Instruments

Grasping/dissecting instruments include forceps, needle holders, coagulators and clamps. This group includes a wide array of instruments that often have multiple uses. Length of the handle is primarily one of surgical preference. However, the longer the handle the more tiring it is to hold for prolonged periods of time. To limit the effect of fatigue, several manufacturers have counterbalanced their instruments to reduce the weight of the tip of the instrument and therefore produce less fatigue.
Forceps can have straight tips, curved tips, tapered tips and grasping tips (Figure 7). However, they should be non-toothed (grasping forceps may be an exemption), have precisely aligned tips, be made of a non-glare material and have a graded closure. They are often used for grasping of tissue, dissection and dilation of tubular structures.
Needle holders are used often for dissection around small vessels. This is due to their finely rounded tips that protect the vessel from injury (Figure 8). When used for placement of microsutures they can be either locking or non-locking. The locking variety allows for loading and holding of a suture in preparation for its use. This is particularly useful for microsurgeons operating without trained assistants. Needle holders usually have curved tips with flat surfaces to securely grasp the suture. Their handles are rounded and are serrated to provide a non-slip surface for precise control.
Coagulators are required to stop bleeding from the small arterioles and allow for visualization of small structures. Only bipolar coagulation should be used to limit coagulation to a precise structure. Unipolar coagulation produces a wide area of coagulation due to the ground current produced (Figure 9 ). A physiologic saline solution should be used during coagulation to limit the build up of tissue debris on the bipolar tips as well as to rapidly cool surrounding tissue to prevent injury by heat conduction. The fine tips of the coagulator are needed for accurate coagulation and are easily damaged. These fine tips should be checked prior to use. A backup pair should be readily available.
Clamps are used to approximate tubular structures and allow for a precise, leak-proof and tension free anastomosis to be made. They are essentially composed of two microvascular clamps mounted on an adjustable bar. The modification we find most useful has small, blunted posts mounted on the concave surface of the clamp(5). This eliminates slippage of the tissue during anastomosis (Figure 10).

Scissors
Scissors are used both for cutting of tissues and sutures as well as dissection. When used for cutting the tips are usually pointed (Figure 11a). Care must be taken to prevent injury to surrounding structures. A scissor used for cutting sutures should be so identified and not used for tissue. Scissors use for dissection should have blunted tips (Figure 11b). When used for dissection their handles are rounded and are serrated to provide a non-slip surface for precise control. When used for cutting a flat handled scissor provides the best control in a single plane. Curved tips are useful when cutting fascia which overlies delicate structures.

Accessory Items for Microsurgery
Useful options for urologic microsurgery include irrigators, operating platforms, background materials and microsponges. Irrigators are necessary to provide an optically clear field. The irrigating solution used is most commonly a physiological saline (we prefer lactated ringers). This solution is drawn up into a 10 cc syringe to which an angiocath tip 21ga or smaller is attached. At least two of these irrigators are kept ready on the field. An operating platform is useful when approximating tubular structures (e.g., vasovasostomy, vasoepididymostomy). We usually use a sterile tongue depressor which has been snugly placed inside a penrose drain of the same length. Background materials are useful in providing a contrast between the operating platform and the tissues. We commonly use a blue background material placed between the tongue depressor and the translucent penrose drain which covers it. Microsponges are often made in the shape of a triangular spear and extremely useful for absorbing fluids and removing small clots.

Acknowledgement: The author would like to thank Mr. Peter Horenz of Carl Zeiss, Inc., Thornwood,NY for reviewing the manuscript and his many helpful suggestions.


REFERENCES:

1. Wagenknecht L. Microsurgery in Urology.New York: Thieme, Inc., 1985

2. Horenz P. Personal Comunication., Carl Zeiss, Inc., 1993:

3. Forster B. Optical magnification and reproduction sytems. In: Wagenknecht L, ed. Microsurgery in Urology. New York: Thieme Inc., 1985: 2-16.

4. Gilbert BR, Goldstein M. New directions in male reproductive microsurgery. Microsurgery 1988;9(4):281-5.

5. Goldstein M. Microspike approximator for vasovasostomy. J Urol 1985;134(1):74.