Arthroscopy in Dogs: Basic Principles
James Tomlinson United States
Arthroscopy has numerous advantages over arthrotomy for diagnosis and treatment of joint disease. Arthroscopy entails less disruption of the periarticular soft tissue. Typically, two or three one-centimeter long skin incisions are required in conjunction with a 5-millimeter diameter tunnel through the underlying soft tissue and into the joint. Decreased soft tissue disruption leads to less pain and less chance for infection. In most cases, return to use of the limb is quicker because of less surgically induced pain. This is especially true when multiple joints are involved and are operated arthroscopically under the same anesthetic episode. Examples of disease conditions where multiple joints are commonly treated under the same anesthetic episode include fragmented medial coronoid process of the elbow and OCD of the shoulder.
Arthroscopy may be employed in a diagnostic, therapeutic or combined modality. Using arthroscopy as an exploratory procedure may prevent the necessity for an arthrotomy and is an important advantage in cases where a surgically treatable lesion is not found. Visualization of the joint typically is better with arthroscopy than with an arthrotomy. In joints like the shoulder and elbow, arthroscopy allows inspection of areas of the joint that is not visible without performing multiple arthrotomies. In addition, the magnification that occurs with arthroscopy in combination with the fluid medium within the joint allows one to see joint pathology that cannot be appreciated with an arthrotomy. Visualization of synovial membrane and cartilage pathology, in particular, is better appreciated with arthroscopy than with arthrotomy. With practice and development of proficiency, the length of an arthroscopic procedure is often less than an arthrotomy procedure. Cosmetic appearance of the dog is typically better after arthroscopy compared to arthrotomy. For some owners, cosmetic appearance is very important.
Disadvantages of arthroscopy are that its use is limited to large joints (large dogs), the equipment is expensive, and considerable training is needed to become proficient with its use. Depending on the specific joint, the dog must be at least 45 pounds lean body weight before an arthroscopy can be performed. Even though the price of arthroscopy equipment is decreasing, one can easily spend $20,000-50,000 for the equipment and instrumentation. Arthroscopy requires advanced hand-eye coordination to be performed proficiently. For most people, proficiency in arthroscopy requires considerable practice. Learning to perform arthroscopy is greatly facilitated by proper instruction by a proficient arthroscopist. Performance of arthroscopy on a regular basis is required to maintain proficiency.
Development of arthroscopic equipment for use in small joints in people has greatly facilitated the advancement of arthroscopy in dogs. The working room inside of a joint of a dog is much smaller than the room in a corresponding human joint. The smaller equipment has allowed not only the exploration of the joint, but also the treatment of various abnormalities. Arthroscopic instrumentation is available from Dyonics (a) Storz (b), Wolf (c) and other companies. Dyonics is the preferred equipment by the author because of its outstanding quality and reliability, broad selection of equipment, and service availability. Purchase of good quality equipment with the latest technology that one can afford is important for optimal results. It is very easy to become frustrated and disillusioned with arthroscopy when using equipment that does not afford clarity of detail and ease of use.
Arthroscopes are available in different diameters, lengths and angles of inclination. The 2.7-millimeter diameter arthroscope is the most commonly used size in dogs. Smaller diameter arthroscopes are useful for smaller joints such as the hock or for larger joints of dogs less than 45 lbs. However, smaller diameter arthroscopes are easier to break than larger diameter arthoscope. Arthroscopes come in various lengths. Dyonics 2.7 mm diameter arthroscopes are available in 67 mm and 120 mm lengths. Short arthroscopes tend to be easier to use in superficial joints like the elbow but may not be long enough for joints like the shoulder of a giant breed dog. The long arthroscope is the best choice for use in a variety of joints especially if only one arthroscope can be purchased. Arthroscopes are available with different viewing angles. Arthroscopes can be purchased with a straightforward view, fore-oblique view (25–30 degrees), and retrograde view (70 degrees). In most cases, the fore-oblique view arthroscope is recommended for canine arthroscopy. The fore-oblique arthroscope allows one to see a different field of view by rotating the arthroscope around its long axis. The fore-oblique view arthroscope also allows visualization “around corners” that are impossible to see with a straightforward view arthroscope. A manual focus ring is present on the arthroscope to allow depth of field adjustment. A video recorder and printer can be used to document the pathology and surgery performed in the joint. Clients like receiving a picture of the arthroscopy and can more easily appreciate the pathology present within the joint. In addition, pictures and videotape are good additions to the medical record and for later review by the arthroscopist. The video recorder and printer are optional pieces of equipment.
The arthroscope is connected to a light source with a fiberoptic cable. The fiberoptic cable allows transfer of light into the joint without transfer of heat into the joint. The fiberoptic cable needs to be compatible with the arthroscope and light source. Light sources are available with either a metal halide or a xenon bulb. The xenon bulb provides the brightest light source and generally is preferred. The light source will have either a manual or automatic adjustment of light intensity. Too little light will not illuminate the inside of the joint well enough to allow adequate visualization. Too much light will produce glare and “white out” making it difficult to visualize joint structures. A light source with an automatic light intensity adjustment is preferred.
Visualization of the inside of the joint is accomplished by either direct view (looking through the end of the arthroscope) or by videoarthroscopy (looking at a video monitor). Videoarthroscopy is the only acceptable method of performing arthroscopy. Videoarthroscopy allows large magnification of the view of the inside of joint, lets multiple people simultaneously see the inside of the joint, prevents contamination of the arthroscope and surgical field, and allows performance of surgical procedures. A miniature video camera attaches to the end of the arthroscope to allow videoarthroscopy. Video cameras currently have 1–3 microchips in the camera. Cameras with either two or three chips are preferred because they provide superior image quality. The video camera is attached to a camera controller that automatically adjusts the video image. A 13–19 inch high definition video monitor is used to view the procedure. Typically, the arthroscope, fiberoptic light cable, light source, video camera, and video monitor should be purchased from the same company to ensure the best image quality and compatibility.
Cannulas are used to allow the tip of the arthroscope to be inserted into the joint. A specific sized cannula is available for each diameter arthroscope. Each cannula has a trocar (sharp tip) and obturator (rounded tip) that fits inside of the cannula that is used to insert the cannula into the joint. A scalpel blade is used to make an incision through the skin and through various depths of the underlying tissue to allow insertion of the cannula with trocar or obturator into the joint. A cannula is necessary to protect the scope from breakage. Cannulas are also used to allow insertion of instruments into the joint. In a typical arthroscopy, one cannula will serve as the arthroscope portal and one cannula will serve as the instrument portal.
A wide array of instruments is available to facilitate joint exploration and surgical procedures. The basic instruments needed for arthroscopy are probes, curettes, and grasping forceps. A motorized bur (shaver) is an indispensable instrument and is used for removing bone, cartilage, and soft tissue. An assortment of blades is available for different uses. An electrosurgical unit used for tissue debridement is a particularly useful instrument when working in the stifle. Capability for intracapsular cauterization of vessels is also helpful in some surgeries. Arthroscopy instruments come in various sizes. Some of the instruments can be inserted through instrument cannulas into the joint. Other instruments require insertion through the tunnel left through the soft tissue after removal of an instrument cannula.
Sterilization of the arthroscope, video camera, and fiber optic light cable is performed by ethylene oxide gas, plasma sterilization, or glutaraldehyde.(d) Metallic instrumentation can be autoclaved.
Basic Arthroscopic Procedure
Arthroscopy utilizes a technique called triangulation. Triangulation is the technique of viewing the inside of a joint from one angle with the arthroscope while manipulating an instrument that is coming into the joint from another angle. Mastering the technique of triangulation requires considerable practice and eye-hand coordination. Triangulation is an essential technique of arthroscopy for performing surgical procedures. Arthroscopy is performed under general anesthesia. Routine preoperative clipping and scrubbing of the leg is performed as for any orthopedic surgery. The author prefers to use a hanging leg procedure (1) so that the entire lower part of the leg can be handled once it has been appropriately draped. Prophylactic antibiotics are typically not used.
Distension of the joint is required to facilitate insertion of the cannulas into the joint. Joint distension and continuous irrigation of the joint allows inspection of the joint, increases working room within the joint, and decreases bleeding within the joint. Fluid is introduced into the joint through a cannula (instrument or arthroscope) connected to a fluid infusion set. Lactated Ringers solution is the fluid of choice.(2) To maintain distension of the joint, the fluid is pressurized. Pressurization can be accomplished by elevation of the fluid, by an inflated pressure bag that fits around the fluid bag, or by a pressurized pump system. Pressure inside of the joint is typically maintained between 40–150 mm Hg. The pressure inside of the joint should be high enough to properly distend the joint but not so high that fluid extravasates into the pericapsular tissue. Collapse of the joint space occurs with pericapsular fluid extravasation. To maintain continuous irrigation of the joint, fluid is allowed to drain through one of the established portals. Joint distension can also be achieved with CO2 or N2O. Specialized equipment is needed for gas distension of joints.
A 20–22 gauge 1.5-inch long needle is inserted into the joint to allow distension of the joint. A pop is typically felt when the needle penetrates the joint capsule. Drainage of joint fluid from the needle confirms intraarticular placement of the needle. A 25 cc syringe filled with an equal amount of lactated Ringers solution and 0.5% bupivacaine with 1:200,000 epinephrine solution is attached to the needle and injected into the joint until resistance is felt. Not all arthroscopists use bupivacaine. The quantity of fluid injected in the joint will vary with the size of the joint but the joint should be tightly distended. A stab incision is made with a No. 11 or No. 15 scalpel blade through the skin and underlying tissue to the appropriate depth. With some joints like the stifle, the incision may penetrate into the joint. Specific locations for insertion of cannulas will vary by joint and the procedure to be performed. A cannula fitted with a trocar is inserted into the joint. The trocar is replaced with an obturator if the cannula needs to be advanced further into the joint. The obturator or trocar is removed and the arthroscope inserted into the cannula. A fluid line is attached to the cannula and fluid irrigation of the joint is performed. After a brief exploration of the joint, an additional cannula is inserted into the joint to allow continuous irrigation of the joint to occur. Additional cannulas can be placed as needed. The joint is further explored and a surgical procedure performed as needed. Manipulation of the leg by an assistant will allow better visualization of certain parts of the joint. At the conclusion of surgery, the joint is thoroughly lavaged to remove any cartilage or bone debris. Bupivacaine can be injected through a cannula into the joint for postoperative analgesia. The skin incisions are closed with one to two simple interrupted sutures.
Use of the Arthroscope in the Diagnosis and Treatment of Lameness
Arthroscopy is usually employed after physical examination and radiographic evaluations have established the diagnosis. In these cases, arthroscopy is used to provide more detailed information about the nature and extent of the condition and may serve as a therapeutic measure. Since a definitive diagnosis cannot always be determined by physical and radiographic evaluations, arthroscopy is useful as a primary diagnostic tool. As previously stated, arthroscopy is particularly well suited to evaluation of the shoulder, elbow and stifle. Diagnostic arthroscopy is especially helpful in establishing the definitive diagnosis of instability associated lesions, bicipital tenosynovitis, presence of an OCD flap versus thickening of the cartilage (shoulder), fragmented medial coronoid process and related joint pathology (elbow), and partial cruciate ruptures, meniscal tears (stifle).
When deciding whether or not to recommend arthroscopy as a diagnostic tool, one must carefully consider the signalment and physical examination findings i.e., the most likely diagnoses, and whether it is possible to diagnose and treat such conditions with arthroscopy. As an example, several diagnoses should be considered in a young Labrador retriever having mild intermittent forelimb lameness and a painful response to elbow manipulation. If only subtle or nonspecific abnormalities are seen on radiographs of the elbow, arthroscopy would be an excellent option because fragmented medial coronoid process of the ulna is a likely diagnosis, and this condition can be detected and treated with this method. Likewise, it would be reasonable to employ arthroscopy in an adult large-breed dog having a painful stifle, but with no cranial drawer sign. Partial rupture of the cranial cruciate ligament with or without concurrent meniscal injury is the most probable diagnosis in this situation. Diagnosis and treatment of this condition is possible using arthroscopic techniques.
Other considerations that must be used to determine if arthroscopy should be recommended is the duration of the problem, the degree of lameness, and response to symptomatic treatment. Typically, the longer the problem has been present, especially with lack of response to medical management, and the more severe the lameness, the sooner arthroscopic exploration of the joint should be recommended.
a) Dyonics, Smith and Nephew, Inc., Andover, MA 01810
b) Storz Instrument Corp., Goleta, CA 93117
c) Richard Wolf Medical Instrument Corp., Rosemont, Ill 60018
d) Cidex, Johnson and Johnson, Arlington, Tx
1. Piermattei DL: An Atlas of Surgical approaches to the Bones and Joints of the Dog and Cat (ed 3). Philadelphia, PA, Saunders, 1993, pp 3-14
2. Reagan BF, McInerny VK, Treadwell BV, et al: Irrigating solutions for Arthroscopy. J bone and Joint Surg Am 65A(5):629-631, 1883
WSAVA Contact Information