Arthroscope

Arthroscopes are commonly described by three measurements: telescope diameter, distal lens angle (viewing angle), and working length (Figure 71-1). The telescope diameter is the outer diameter of the tubular portion of the arthroscope without the accompanying cannula. Arthroscope diameters commonly used in small animal arthroscopy include 1.9 mm, 2.3 mm, and 2.7 mm (Figure 71-2). Arthroscopes with smaller telescope diameter minimize joint trauma and are more easily manipulated in joints that are highly congruent and have limited joint space, such as the canine elbow and hock, than are arthroscopes with larger telescope diameter. Arthroscopes with larger telescope diameter permit a larger field of view and offer greater resistance to bending and, therefore, greater durability.

Lens angle is the angle between the center of the viewing range and the axis of the telescope (see Figure 71-1). The angles most commonly available in arthroscopes are 0 degrees, 30 degrees, and 70 degrees. Beveling the lens of the arthroscope increases the field of view and enables examination of a larger area of the joint simply by rotating the arthroscope. The 30 degree arthroscope is the most common type used in canine arthroscopy. Rotation of a 30 degree arthroscope allows the equivalent of a 60 degree field of view (Figure 71-3). Working length, which is the overall length of the shaft of the telescope, is usually designated as “short” or “long.” Short arthroscopes have a working length of approximately 8.5 cm; long arthroscopes have a working length of approximately 13 cm. Short arthroscopes provide adequate length for most small animal arthroscopy with the possible exception of the canine hip joint.

The ocular (or near) end of the arthroscope includes an eyepiece or camera mount, a light source post, and a cannula interlock (Figure 71-4). The connection between the arthroscope and the camera is available in two styles. The most common type uses a spring-loaded clip that enables quick attachment of the arthroscope to the camera. The other type is a direct-coupling, or “glass-on-glass,” system, in which the arthroscope is coupled to the camera using a threaded interface (Figure 71-5). The internal designs of most arthroscopes are similar, and only modest differences have been noted in the quality of the optics; however, individual surgeons often develop preferences based on arthroscope size, length, and design.

The light post is the site of attachment of the fiberoptic cable that transmits light from the light source to the arthroscope. Light post connections are available in threaded and snap-on varieties, and adaptors are available to accommodate various cable designs. Once light reaches the arthroscope, it is transmitted into the joint by optic fibers that typically are located along the internal periphery of the telescope. Illumination allows viewing of an image, which is transmitted to the camera through the lens in the central portion of the telescope.

Irrigation

Constant, reliable flow of fluid across the tip of the arthroscope and through the joint is vital for adequate visibility. Fluid expands the joint, provides a clear field of view, and flushes the joint of debris and contamination. By distending the joint and thereby increasing intra-articular pressure, irrigation provides a tamponade effect to minimize bleeding during the procedure.

Numerous studies have evaluated the effects of fluid type and temperature on cartilage and patients undergoing arthroscopy.1,7,29,39 Saline and lactated Ringer’s solution both have been used for arthroscopic irrigation, and several studies have shown no difference between the effects of these fluids on cartilage metabolism; however, other studies have suggested that lactated Ringer’s solution may be more physiologic for cartilage and may have fewer negative effects on the meniscus than saline.³² Cold irrigation fluid may aid in achieving hemostasis and in minimizing thermal damage if radiofrequency or electrocautery is used; however, cold arthroscopic irrigation fluid has been shown to affect patient core temperature in human arthroscopy.^5,8

Irrigation systems must deliver fluid with sufficient pressure to distend the joint and maintain flow without increasing the extravasation of fluid into periarticular soft tissues. Fluid enters the joint through the space between the telescope and the cannula. In some cases, a separate inflow cannula may be used to introduce large volumes of fluid. Indications for the use of a separate inflow cannula include lavage of a blood-filled or septic joint, where large-volume lavage is particularly beneficial to aid in removing debris. With any irrigation system, fluid usually must be pushed into the joint under pressure to achieve adequate flow. The intra-articular pressure necessary for arthroscopy varies, depending on the joint and the purpose of arthroscopy. However, most studies suggest that 60 mm Hg is a reasonable starting pressure.³⁵ Excessive pressure can cause soft tissue injury and extravasation into periarticular tissues. No studies are investigating appropriate irrigation fluid pressures for canine arthroscopy. Fluid may be pressurized by gravity flow or with an electric fluid pump. Both systems have advantages, and selection often depends on the joint being operated on, as well as surgeon preference.

Gravity flow is seen in administration of fluid directly from a fluid bag to the cannula with a simple administration set. The diameter of the administration set tubing determines the fluid flow rate. Large-diameter tubing allows a higher flow rate and is available specifically for arthroscopy. The rate of fluid flow may be increased by placing the fluid bag in a pressure bag or by elevating the fluid bag. Elevation of fluid bags to as high as 8 or 9 feet is recommended to achieve adequate hydrostatic pressure.² Use of a 3 or 5 L bag may improve pressure and decrease the need for a technician to replace fluid bags or reinflate pressure bags. Also, Y-adaptors permit multiple bags to be connected at the beginning of the surgical procedure. Advantages of gravity flow include the relative simplicity of the system, low cost, and safety against overpressurization. Gravity systems are easy for the surgeon and technician to learn and to use. In addition, they are easy to maintain and do not require additional space in the operating room or on the arthroscopy tower. Most small animal arthroscopy procedures can be accomplished with gravity flow.

Fluid pumps permit selection of both fluid flow rate and fluid pressure (Figure 71-10). Most use pressure priority, which means that selected pressure in the joint will be maintained, and when the pressure drops below this level, fluid will be pumped into the joint to maintain the selected intra-articular pressure. Fluid pumps are superior to gravity in maintaining pressure when suction or shaver systems are in use, as use of these systems can result in the rapid removal of fluid, a sudden decrease in intra-articular pressure, and collapse of the joint. Disadvantages of fluid pumps include their initial cost and the cost of administration sets, the moderate complexity of tube setup, and the space requirements.

Irrespective of the method of fluid administration used, the surgeon must be aware that flexion of a distended joint will increase intra-articular pressure. Aggressive manipulation of a distended joint may result in injury to the synovium and periarticular soft tissues.

Egress Systems

Adequate outflow of fluid, or egress, must be established to maintain appropriate fluid flow through the joint during arthroscopy. Egress may be achieved by permitting outflow through an instrument portal or by inserting a specific egress instrument. Few disadvantages are seen in permitting egress only through an instrument portal, as long as it provides adequate flow. This technique does require establishing the instrument portal early in the procedure, regardless of whether or not instruments will be used. Alternatively, a specific egress tool may be inserted into the joint. In smaller joints, this is often a hypodermic needle; in larger joints, it is often a multifenestrated cannula (Figure 71-11). One advantage of an egress tool over use of the instrument portal is that a needle or cannula can be blocked intentionally to pressurize the joint, if needed. A second advantage is that tubing may be attached to the end of the needle or cannula to scavenge fluid, although this may inadvertently establish a siphon that can alter fluid flow in the joint and introduce air bubbles. The disadvantage of use of an egress needle or cannula is the potential for additional iatrogenic damage to the joint, along with the need for additional instrumentation in and around the joint.

In most cases, fluid is not scavenged from the egress portal but is allowed to flow onto the operating room floor. The patient may be protected from moisture and subsequent secondary hypothermia with the use of clear plastic sterile adhesive draping systems (e.g., SteriDrape 3M, St Paul, MN) (Figure 71-12). Fluid can be removed from the floor with the use of commercially available floor suction devices (Figure 71-13).

Hand Instruments

Hand instruments are necessary for performing arthroscopic treatments. The most commonly used hand instruments are graspers, punches, curettes, knives, awls, and probes. Hand instruments for small joint arthroscopy must combine small diameter with excellent mechanics to provide high accuracy and reliability while minimizing the likelihood of iatrogenic trauma and instrument failure.

Grasping forceps are available as locking and nonlocking types (Figure 71-14). Nonlocking types include standard alligator forceps and those designed specifically for arthroscopic use. Most grasping forceps designed for arthroscopic use have an enclosed operating mechanism that avoids interference between the mechanism and surrounding tissues.

Graspers vary in size and length, and selection depends on the joint, the specific procedure being performed, and the preference of the surgeon. For most small animal applications, pointed forceps without teeth are recommended (Figure 71-15). Locking forceps are advantageous in many arthroscopic procedures involving removal of bone chips or cartilage flaps. Many forceps designs are available in long and short lengths. Again, selection is based primarily on surgeon preference, although a shorter working length is recommended for smaller joints.

Biting, or punch, forceps are used to biopsy or debride soft tissues (Figure 71-16). Punch forceps have a sharp, hollow lower anvil and an upper punch that is used to remove small pieces of soft tissue, including synovium and meniscus. Variations in design include straight and side biting, as well as differences in diameter and length. A small- or medium-diameter straight punch forceps is useful in small animal arthroscopy for debriding synovium that is obscuring the view, for obtaining a synovial biopsy specimen, and for debriding a meniscal injury.

Small-diameter curettes are critical in small joint arthroscopy. These instruments are used to elevate bone fragments and to debride cartilage and bone. A small (5-0) surgical curette or arthroscopic curette is appropriate in most situations (Figure 71-17).

Arthroscopic knives are useful in small animal arthroscopy for treating meniscal injury, performing tenodesis, and cutting soft tissue attachments to bony fragments. Knives may be straight, curved, or hooked; the choice depends on the procedure being performed. Specific designs of arthroscopic knives include meniscal and banana knives (Figure 71-18).

Microfracture of the subchondral bone bed is routinely performed with angled awls or micropicks and a mallet. Micropicks may be straight or angled (Figure 71-19).

Most probes are of a right-angle design with a tip that is approximately 3 mm long (Figure 71-20). Probes are used to palpate surfaces and manipulate tissues within the joint. In small animal arthroscopy, right-angle probes are used to palpate articular cartilage to detect pathology and to manipulate cartilage flaps, meniscal injuries, and bone fragments. Most probes have measurement markers that aid in reporting and imaging the size of lesions.

Instrument Cannulas

Arthroscopic instruments may be inserted into the joint through a portal with or without a cannula (Figure 71-21). The major advantage of working through a cannula is the ease of instrument insertion. Without a cannula, it may be difficult to switch instruments and identify the portal, particularly if the portal was poorly made. Repeated attempts to insert an instrument through a poorly defined portal can lead to soft tissue trauma and fluid extravasation. The major disadvantage of using a cannula is that some instruments may be too large to permit insertion through the cannula. No general consensus has been reached on the use of cannulas in small animal arthroscopy, although anecdotally it appears that most surgeons do not routinely use them. Instrument cannulas are available in numerous diameters and lengths. For small animal arthroscopy, cannulas with an inner diameter of 2.3 to 3.5 mm and a length of 4 to 5 cm are most appropriate. Most cannulas come with both sharp (trocar) and blunt obturators. The blunt obturator should be used to minimize iatrogenic trauma during insertion of the cannula.

Cannula systems should include a set of switching sticks or tubes. This system permits progressive dilation of the portal and subsequent insertion of larger cannulas. To use this system, a relatively small cannula, with an obturator, is inserted into the joint. A switching stick is placed through the cannula, and the cannula is withdrawn. A larger cannula or dilation tube is placed over the stick, and the process is repeated until the desired cannula is in place. The use of cannulas depends on the joint, the instruments being used, and the surgeon’s preference. Although a cannula system generally is not necessary for small animal arthroscopy, it is useful to have a system available for special situations, and it may be easier for beginning arthroscopists to work through cannulas.

Joint Distractors

The use of instruments to distract the stifle joint has been described to aid viewing of the caudal horns of the menisci. A narrow Hohmann retractor or an angled micropick can be used intra-articularly to lever the proximal tibia cranially, improving the view of the caudal portion of the joint. An external distraction device using transcortical pins has been reported to achieve stifle joint distraction (Figure 71-22).^6,14

Limb Positioners

Limb-positioning devices are commonly used in human arthroscopy and aid in providing accurate and stable limb positioning, while minimizing the number of individuals in the operating room. Limb-positioning devices for canine arthroscopy have been described for the stifle, elbow, shoulder, and hip (Figures 71-23 and 71-24).³¹ Stifle and elbow positioners are manufactured from a photographic clamp and arm device (Bogen Magic Arm and Super Clamp, Ramsey, NJ) and custom manufactured braces.

Power Hand Tools

Power shavers are designed to rapidly debride soft and hard tissues (Figure 71-25). Power shavers include a control box, a handpiece, and a shaver tip. Most shavers permit the operator to vary both the speed and the direction of the instrument, and options include forward, reverse, and oscillation. Speed control is important because different tissues require different approaches. Controls may be located on a foot pedal or on the handpiece.

The handpiece connects the shaver to the control box (see Figure 71-8) and to suction. A suction regulator may be found on the handpiece as well. Suction improves the function of the shaver by pulling soft tissues into the cutting blade and removing debris from the joint. The handpiece is supplied by an electrical cord that has a capped connector that inserts into the control box.

Shaver tips are available in numerous styles that are designed for soft tissue or hard tissue debridement (Figure 71-26). Soft tissue shavers include guarded sharp cutters and aggressive cutters. Sharp cutters have a simple sharp-edged cup, whereas aggressive cutters have a toothed cup. The toothed cup is more useful for debridement of fat or synovium in small joints. Most shavers have several options for operation, including a forward and a reverse direction, oscillation, and variable speed. When an aggressive cutter is used to debride the fat pad of the stifle joint, suction is applied and the shaver is operated in oscillation to optimize soft tissue debridement. Operation of the shaver at higher speeds limits the amount of tissue that can be drawn into the blade. Shaver tips used for debridement of bone include round and oval guarded burrs. Shaver tips are two-piece units that are separated for cleaning.

Electrocautery and Radiofrequency Devices

Electrocautery and radiofrequency are used to generate heat for cauterization of vessels, debridement of tissues, or shrinkage of collagen (Figure 71-27). Electrosurgical tips specifically designed for underwater arthroscopic application are available for use with standard electrocautery generators (Figure 71-28). These instruments may be used for cautery of small vessels, and special tips are designed to cut soft tissues. Extreme caution must be taken during the use of electrocautery, as the heat generated can easily and rapidly damage ligaments, cartilage, and arthroscopes.^18,19

Radiofrequency devices transfer energy by using electromagnetics to produce molecular friction in the intracellular and extracellular environment. Monopolar units generate an alternating current that runs from the tip of the probe to the joint capsule or another surface, through the body, to a grounding plate. Heat is generated in the tissues because of their high resistance. Bipolar units create an arc of energy through the arthroscopic fluid that can be directed through tissues.

Joint capsule collagen is primarily type I. When radiofrequency probes are used on a joint capsule, collagen undergoes denaturation in response to heating in association with breakage of some cross-links within the triple-helix structure. Cross-links between collagen molecules are maintained and cause contraction, or shrinkage, of the tissue.

The effects of radiofrequency on shrinkage and tissue strength depend in part on the temperature of the probe. Optimal temperatures range from 65° to 75° C. Higher temperatures cause greater weakening of tissues. Collagen and tissues undergoing shrinkage are weaker than normal for 6 to 12 weeks after the procedure. In addition, it is not known how long shrinkage of treated tissues persists. Although shrinkage by as much as 50% can be achieved experimentally, clinical shrinkage normally ranges from 15% to 25%. In addition to causing shrinkage, a radiofrequency unit may be used to ablate tissues, including proliferative synovium, torn or damaged meniscus, and partial-thickness cartilage lesions.18,19

The use of radiofrequency probes for management of shoulder joint instability has been reported in the dog.²⁴ Current use of radiofrequency equipment in small animal arthroscopy appears to be limited owing to the severe damage that may be caused to cartilage and limited studies demonstrating the long-term efficacy of these techniques.

Other Basic Equipment

An arthroscopy tray should include basic equipment necessary for arthroscopy of most joints, including hypodermic needles (20 or 18 gauge, 1 and 1.5 inch), syringes (6 mL recommended), fluid bowl, small and large straight hemostats for portal dilation, blunt towel clamps for securing cables, and needle holders and suture scissors for closure.

Anesthesia and Analgesia

Specific selection of an anesthetic protocol (see Chapter 24) for a patient undergoing arthroscopy is dependent on the age and medical status of the patient, as well as on the joint to be operated. A majority of patients undergoing arthroscopy are young or middle aged and otherwise healthy. Preanesthetics routinely include a sedative (acepromazine, valium) and an analgesic (opiates and/or nonsteroidal antiinflammatory drugs [NSAIDs]). Induction agents may include propofol or etomidate. Following induction, additional analgesia for hindlimb procedures can be provided with epidural administration of an opiate (preservative-free morphine), a local anesthetic, or both. Many procedures may be done on an outpatient basis; therefore short-acting inhalant anesthetics such as sevoflurane may be particularly appropriate. Postoperative analgesia may include additional opiates during hospitalization, with NSAIDs, tramadol, or both continued as necessary once the patient is discharged from the hospital.

Patient Preparation

Surgical preparation for small animal arthroscopy depends on the joint to be operated and whether additional procedures will be performed. For example, when arthroscopy is performed on the elbow or shoulder joint, it is uncommon for joint additional open surgical procedures to follow, whereas stifle joint arthroscopy is frequently followed by a tibial plateau leveling osteotomy or other stabilization technique, and hip joint arthroscopy may be followed by a triple pelvic osteotomy. When arthroscopy alone is performed, the surgical clipping and prepping may often be very limited in comparison with an open approach; however, when one is first learning arthroscopy, it is recommended to provide sufficient skin preparation to allow an arthrotomy to be performed if necessary. Clipping recommendations may be found in the individual joint sections of this chapter.

Patient positioning for arthroscopy varies with the joint to be operated and the specific arthroscopic approach to be used. Most small animal arthroscopy procedures can be performed through described portals and positioning. One exception is the shoulder joint, which may be approached laterally or medially. The approach is determined by the condition being treated.

Proper joint positioning and distraction are critical to the success of arthroscopy and minimization of iatrogenic joint trauma. Positioning and distraction may be achieved with the aid of an assistant or with the use of positioning devices,³¹ which have known advantages and disadvantages. Devices occupy less space and represent a lower long-term cost; in addition, devices do not fatigue or move inadvertently; however, positioning devices do not allow rapid changes in joint distraction or angle. Positioning and distraction vary with the individual joint and are discussed in detail in specific joint sections of this text. Positioning of the equipment and in particular the monitor should be done in such a way that the surgeon can easily see the monitor at all times.