Arthroscopy Basics

An arthroscopic system is nothing more than a method to attach a camera to the end of the scope and project the images to a monitor. First, one must understand the importance of camera orientation upon one's ability to maintain a point of reference within the joint. Just as with any video camera, if the camera is right side up, the individuals in the room will accurately appear to be standing on the floor and one's ability to systematically evaluate the room with the camera is quite simple. If, however, the camera is sideways, the persons in the room will appear to be standing on the wall and one's ability to systematically move about the room with the video image is seriously compromised. Typically, an arthroscopic camera is right-side up when the buttons are on top and the camera is maintained in this orientation. Next, one must understand that the end of the typical arthroscope is not flat, but is bevelled 30 degrees. This bevel means that the image visualised from the tip of scope is not as though one is looking through a pipe; rather it is as though one is looking through the periscope of a submarine. One can rotate the scope to look around the joint.

One must appreciate the importance of depth of field when performing arthroscopic surgery. To understand this concept, imagine that I am looking at a friend across the room and I immediately recognise her. As I move ever closer, a pimple (spot) on her ear lobe comes into view. As I get closer still, I can see amazing detail of the pimple and her ear lobe, but I can no longer tell to whom this pimple-covered ear belongs. As I get closer still, I can see the white dome of the pimple, but I have no context that it is attached to an ear or even that it represents a pimple because all I see is white. The ideal arthroscopic depth of field is close enough to visualise the lesion and far enough to have appropriate context and orientation.

Arthroscopic surgery requires proper fluid flow into and out of a joint. Ideally, the flow rate into and out of a joint allows distension of the joint and lavage to maintain a clear visual field. Too little flow and the joint is not adequately distended or lavaged to allow visualisation. If the fluid flow into the joint drastically exceeds the flow out of the joint, fluid will extravasate into the surrounding tissues and, ultimately, collapse the joint.

Equipment Needs

To perform diagnostic elbow arthroscopy, one's arthroscopic system should include the following: an arthroscopic camera with quality colour monitor, a 1.9mm, 30-degree, short arthroscope with compatible cannula/blunt trocar and light source, lactated Ringer's bags and sterile administration tubing and a photo documentation system. With gravity flow or pressure sleeve administration of fluid, the fluid flow will decrease as the pressure inside the joint approaches that of the fluid administration system. Gravity flow has the disadvantage of not always being able to distend the joint or lavage the joint as well as one would like (can be a problem in smaller joints like the elbow), but the risk of extravasation of large volumes of fluids is reduced.

Optional equipment for diagnostic arthroscopy includes a fluid pump for controlled inflow of fluid. Fluid pumps may be volume-controlled or pressure-controlled. Volume-controlled pumps deliver a set volume of fluid/minute regardless of the amount of pressure that develops within the joint and there is risk of extravasation. Pressure-controlled pumps are set not to exceed a specified pressure and to reduce the risk of fluid extravasation.

To perform basic therapeutic elbow arthroscopy, the following instruments are needed: a blunt probe (or 'switching stick'), a fine curette (5-0 and smaller), right-angle probe, small graspers, fine-tipped mosquito haemostats (straight and curved), small arthroscopic osteotome, arthroscopic micropick and mallet. A hand burr is also quite helpful. A power arthroscopic shaver is helpful for more advanced arthroscopic surgery.

Basic Training

Simple simulators (scoping the inside of a green pepper) can be used to learn importance of camera orientation, use of the 'periscope effect' and development triangulation manipulative skills. Triangulation refers to the ability to deliver an instrument (such as grasper) into the field of view and perform the desired manoeuvres (grasping and excising the fragment within a confined space). It is important not to have the instrument too close to the arthroscope/camera head or the latter will interfere with freedom of movement of the former. Conversely, instrumentation orientated at right angles, or worse yet, 180 degrees to the arthroscope makes manipulations quite difficult.

Enrolment in a basic arthroscopy course is essential to develop basic skills in arthroscopic surgery that can then be reinforced through regular 'practice sessions' on cadavers. Once the veterinary surgeon is ready to make the leap to clinical cases, it is advisable to prepare pet owners for the likelihood of conversion to an open arthrotomy. A surgical assistant who is familiar with the instrumentation and basic steps of arthroscopic surgery is also recommended.

Patient Preparation for Elbow Arthroscopy

The patient is clipped and prepared for open arthrotomy in the event that arthroscopy must be aborted. The dog is positioned in dorsal recumbency with sandbags placed along the edge of the table to function as a fulcrum to distract the medial joint space. For therapeutic arthroscopy, right-handed surgeons will initially be more comfortable working on dogs' left elbows.

Instrumenting the Elbow

After draping, the assistant abducts the limb firmly against the sandbag fulcrum. Firm pronation of the elbow will further distract the medial joint space. A 3 ml syringe and 22 gauge needle are placed distal to the medial epicondyle (at the level of the joint space) and several millimetres caudal. The needle should pass cleanly and directly into the joint (if the needle must be angled to hit the joint, it should be reinserted). Joint fluid is aspirated to confirm proper placement. The needle is left in place and lactated Ringer's solution (some surgeons prefer bupivacaine or bupivacaine with epinephrine) is injected until the joint is distended and pressurised (volumes of 5-12 ml are typical) as detected by reverse pressure felt on the plunger. The position of the needle marks the desired location for the arthroscopic portal and the assistant must be careful not to alter the position of the limb at this time. A no. 11 blade is advanced as a proximodistally orientated stab incision at the level of the needle. As the needle is withdrawn, the arthroscope cannula and blunt trocar are advanced through the stab incision into the elbow joint. After entry into the joint, the trocar is removed from the cannula and fluid should flow freely. The arthroscope is inserted into the cannula and the fluid ingress line is attached. Blood contamination in the joint may obscure ideal visualisation at this point. Establishing an outflow (or egress) portal will allow joint lavage to clear the view. An 18 or 20 gauge needle is advanced along the deep edge of the medial epicondylar ridge and directed toward the anconeal process. Free flow of fluid (if the ingress line is open and pressurised) and a clearing of the arthroscopic image confirm penetration of the joint. If gravity flow is used, a 10-drop/ml administration set is used. If a pressure-controlled fluid pump is used, relatively high pressures (60-70 mmHg) and low volume can be used in the elbow. Outflow tubing can be connected to the needle to direct outflow of fluid into a canister on the floor if desired. This instrumentation will allow diagnostic arthroscopy and image-capture documentation of the anconeal process, trochlear notch, coronoid process (lateral and medial aspects), radial incisure, radial head and medial and central aspects of the humeral condyle.

For probing or treatment of the medial coronoid process (MCP), an instrument portal is established. First, a 22 gauge needle is passed into the joint at the same proximodistal level as the scope and approximately 1.5 cm cranial to the scope. Fluid flow from the needle confirms intraarticular placement, but visualisation of the needle at the level of the MCP with the surgeon's hands spaced comfortably apart is essential before proceeding. The arthroscope is held in a fixed location visualising the MCP and the needle is repositioned until these criteria are met. The most common reason for failing to visualise the needle is the needle crossing the scope in the joint ('chop sticks'). It is surprising how relatively parallel the needle and arthroscope must be. A no. 11 blade is passed into the elbow joint alongside the needle once it is properly orientated, Next, a switching stick is placed into the stab incision as the needle is removed to establish the instrument portal. Similarly, a haemostat can be passed into the incision and gently opened to dilate the portal. A relatively large, clean portal will allow for free passage of instruments (without need for a cannula) and free outflow of fluid (so that extravasation into the subcutaneous tissues is minimised).