Arthroscope

Advances in technology have resulted in improved arthroscope design and function. The arthroscopes used today have improved optics and field of view with smaller diameter lenses, and they use fiberoptic and digital technology to improve visualization. The arthroscope is designed to fit inside a cannula, which is inserted into the joint with use of a blunt trocar. Modern cannulas allow the flow of irrigation fluid into the joint. The camera is housed within the arthroscope and connected to the digital monitor for direct visualization of the joint, whereas the light source is coupled using fiber-optic cable. Arthroscopy systems typically allow the surgeon to record both digital images and video.

Arthroscopes are differentiated on the basis of optical characteristics, which include the lens diameter, field of view, and angle of inclination. The diameter of the lens determines the size of the arthroscope and the field of view and can vary from 1.7 to 7 mm. The field of view is represented by the total angle visualized by the lens of the arthroscope, with a larger lens diameter allowing a greater field of view. The angle of inclination is defined as the angle between the long axis of the arthroscope and a line perpendicular to the lens and can vary from 0 to 120 degrees. The advantage of using angled arthroscopes is that they provide better control and allow a wider field of view with rotation of the arthroscope, but a central blind spot directly in front of the arthroscope is created with arthroscopes that have a higher angle (70 to 90 degrees). The degree of magnification of an object viewed with an arthroscope is determined by its distance from the lens. This characteristic makes judging arthroscopic distances and sizes difficult, but the use of an object of known size for comparison (such as a probe) can be of assistance.

The most commonly used arthroscope is 4 mm in diameter and has an angle of inclination of 25 to 30 degrees. Smaller joints can be accessed using arthroscopes with a smaller diameter (1.9 or 2.5 mm). Arthroscopes with increased angles of inclination (70 or 90 degrees) can be used to view difficult areas such as the posterior corners of the knee.

The fiber-optic light source and power console for shavers and drills are typically housed on an arthroscopic cart. Such a cart can be positioned easily in the operating room so it is close to the patient but does not obstruct personnel. Arthroscopy using modern equipment requires a light source capable of producing 300 to 350 watts, for which tungsten, halogen, and xenon arc sources have been adapted. Fiber-optic cable uses bundled glass fibers to transmit light from the source to the arthroscope. The intensity and quality of light are diminished by the length of cable or damage to it, although modern fiber-optic cables are more durable.

Reduction of camera size, improved camera resolution, digitization of the video signal, and the integration of high-definition technology have all contributed to considerable improvement in the quality of visualization obtained using arthroscopy. The video monitor connected to the camera can either be on the arthroscopic cart, or in more modern operating rooms, it may be integrated into the room on mobile supports. Many modern operating rooms are now equipped with high-definition monitors.

Fluid Pump

Irrigation is vital for arthroscopy because it is responsible for joint distension, removal of debris, and improvement of visualization. Joint distension is supplied by the hydrostatic pressure of the irrigation fluid, which can be maintained using gravity or mechanical pumps. Every foot of elevation of the irrigation solution above the joint results in approximately 22 mm Hg of pressure. The use of a fluid pump allows more precise control of the rate of flow and hydrostatic pressure in the joint and can be used to minimize extravasation of fluids into the tissues. A physiologic solution such as Ringer’s lactate or normal saline should be used for irrigation; the surgeon decides which solution to use. The addition of epinephrine to the irrigation fluid (1 mg/L) has been shown to decrease bleeding and improve visualization ( Fig. 11-1 ).

The arthroscopic cart with camera, monitor, light source, power for shaver and handpieces, and pump.

Fluid management in arthroscopy consists of balancing the flow of fluids in and out of the joint. This balance is vital to maintain appropriate distension of the joint without causing excessive fluid extravasation into the tissues, and it plays a role in the management of bleeding, visualization, and debris clearance. An imbalance between inflow and outflow can occur when the motorized shaver is being used, resulting in turbulence in the joint from the increased outflow through the shaver. To prevent this problem, the inflow rate can be increased, the outflow through the suction or arthroscope can be decreased (or closed to prevent back flow), or outflow through the shaver can be decreased by ensuring that the window is occupied with tissue to be cut.

Instruments and Motorized Shavers

A variety of hand-operated instruments are used in arthroscopy. Many are generalized, but some instruments have been developed for particular joints or procedure-specific tasks. These instruments include various arthroscopic probes, graspers, baskets, scissors, knives, suture passers, and radiofrequency instruments. The actual instruments required for arthroscopy depend on surgeon preference, the particular joint involved, and the procedure being performed ( Fig. 11-2 ).

A basket forceps for meniscal resection.

Arthroscopic Probe

Second only to the arthroscope itself, the probe is the most important and utilized instrument in both diagnostic and therapeutic arthroscopy. Most probes are right angled at the working end, with a tip length of 4 mm that can be used to estimate intraarticular size, depth, and distance. Its primary purpose is palpation and identification of pathology, such as soft cartilage, loose bodies or cartilage flaps, meniscal tears, or insufficient tension of the anterior cruciate ligament. It is also a useful instrument for learning triangulation, planning surgical approaches, and positioning or retracting intraarticular structures or loose bodies. Care should be taken when palpating structures with the arthroscopic probe, because use of the tip may cause injury to tissues, and therefore use of the elbow for such activities is advisable.

Basket Forceps

Basket forceps are commonly used in procedures that involve the removal of intraarticular tissue, such as a meniscectomy. Basket forceps have a central opening and remove a portion of tissue that is then allowed to fall free into the joint, eliminating the need to remove the instrument from the joint to clear the basket each time. These forceps typically range in size from 3 to 5 mm and are available in straight, left or right curved, and up and down angled varieties to facilitate work in different areas. Left and right curved varieties enable the surgeon to access the anterior portion of the meniscus, whereas the up and down angled instruments permit trimming of the posterior meniscus around the femoral condyles. These instruments are also available in low-profile varieties for work in tight spaces, and some have hooked jaws that prevent tissue from slipping forward between the jaws when they are closed. Proper technique with these instruments is to use the jaws to remove small pieces of tissue, because too large of a bite will strain the mechanical joints and may damage the instrument.

Grasping Forceps

Grasping forceps are used to securely hold, apply tension to, or retrieve intraarticular materials. These forceps are available in jaw configurations that include numerous serrated interdigitating teeth or with one or two sharp hooks at the distal end of the jaws. Configuration of the grasping jaws can also differ, in that varieties exist with both or only one mobile jaw. The graspers with forceps that have both jaws mobile are more suited to grasping and gripping larger intraarticular objects.

Scissors

Arthroscopic scissors are available in small and large sizes and with both straight and hooked blades to ensure an appropriate instrument for each situation. Hooked blades are easier to use compared with straight blades, because they prevent the tissue from being pushed out from between the blades during the cutting motion. Curved and angled options, in which the shaft and blades are curved or the blades deviate from the shaft, respectively, are also available for difficult-to-reach resections.

Knives

Disposable arthroscopic knives are available in various shapes and sizes and should always be used with a cannula to protect the tissues during joint insertion and removal. Blade varieties include straight, curved, end-cutting, and hooked, all of which allow the appropriate instrument for each situation. An important and useful characteristic of many arthroscopic knives is that the blades are magnetic to facilitate removal from the joint should it break.

Motorized Shavers

Motorized shavers consist of a pair of cylinders, one inside the other, each with a matching window. The inner cylinder spins within the outer and has an edge to both sides of its window that cuts tissue drawn into the outer cylinder by the attached suction. The removed tissue is then drawn down the inner cylinder, out of the joint, and into a suction trap. Commonly used motorized shavers range in diameter from 3 to 5.5 mm, but a 2-mm option is available for access to smaller or tight joints. Shavers with a larger diameter have larger windows and can expedite removal of tissue. Shavers also are available in various shapes and angles with different blades or burrs, all designed for specific purposes. Control of the motorized shaver is possible either by a hand or foot pedal and allows clockwise, counterclockwise, and alternating rotation to improve the efficiency of tissue cutting and allow clearing of the blade. Practically, when the motorized shaver is in use, the blades should be in the field of view to prevent unwanted damage to normal tissues. It also is advisable to close the outflow from the joint while the shaver is in use to prevent backflow of fluid into the joint ( Fig. 11-3 ).

A typical shaver blade for meniscal resection.

Cannulas and Switching Sticks

Cannulas and switching sticks of numerous sizes are available to assist with the insertion and use of instruments during arthroscopic procedures; they are all designed for use in specific joints. Cannulas are used to maintain the integrity of a portal into the joint so that the intervening soft tissues do not interfere with activities such as knot tying. They also allow easy insertion of instruments without trauma to the tissues through which the portal is made. Switching sticks are used to ease the passage of the arthroscope and cannulas into the joint in question by holding the path through the soft tissues into the joint so that a cannula or arthroscopic sheath can be inserted into the joint over it. When working in joints that are deep from the surface, switching sticks are particularly useful in maintaining these paths.

Electrocautery and Radiofrequency Instruments

Electrocautery and radiofrequency instruments can be used for cutting and shrinking soft tissues and can play an important role in maintaining hemostasis. A variety of these instruments have been developed for use in particular joints or for specific purposes, including some with flexible tips. Electrocautery uses heat directly from the probe to effect tissue changes and has been adapted for intraarticular use with various irrigation solutions.

Radiofrequency instruments generate a high-frequency electromagnetic current at their tip, causing heat to be generated by the resistance to current passage through tissue. Monopolar and bipolar radiofrequency systems have been adapted for arthroscopic use. Monopolar systems allow current flow from the tip of the instrument to a grounding pad on the patient, using the path of least resistance, and generate heat at the tissue closest to the tip. Bipolar devices permit passage of current between two electrodes at the tip of the instrument, heating the tissue between them. The primary difference between the two radiofrequency systems is that monopolar instruments require a grounding pad to allow energy to pass from the body, whereas bipolar instruments pass energy between electrodes at the intraarticular site of interest.

The specific effect of radiofrequency instruments on tissues depends on the amount of heat transferred. Low levels of heat transfer cause collagen, which is the major constituent of most soft tissues, to denature and shrink by as much as 50% of its length. Higher levels of heat destroy collagen and are commonly used for tissue ablation and debridement. Concerns with the intraarticular use of these instruments include penetration depth, temperature control, and cell death, causing cartilage damage or chondrolysis. The penetration depth and area affected are proportional to the power and temperature used.