Diagnostic Imaging

Radiographs can be used to screen for elbow dysplasia, though in cases of medial coronoid process (MCP) fragmentation, the fragment is seldom visualized; thus, secondary changes (subtrochlear sclerosis, abnormal contour of the MCP, osteophytosis, etc.) are often used for evidence of disease. Computed tomography (CT) improves the diagnostic accuracy of many patients with elbow dysplasia.

Arthroscopy Basics

An arthroscopic system attaches a camera head to the end of the scope and projects images to a monitor.¹ Camera orientation is critical to maintain a point of reference within the joint. If the camera is right side up, the top of the projected image corresponds with the top of the field of view and one's ability to systematically evaluate the joint space is quite simple. If, however, the camera is sideways, the top of the projected image corresponds with the side of the scope's field of view and one's ability to systematically evaluate the joint is seriously compromised. Typically, an arthroscopic camera head is "right-side up" when the buttons are on top. Next, one must understand that the end of the typical arthroscope is beveled 30°. This bevel means that the image visualized from the scope is not as though one is looking through a pipe; rather, it is as though looking through a periscope. One can rotate the scope to look around the joint. Next, one must appreciate the importance of depth of field when performing arthroscopic surgery. To understand this concept, imagine that you are looking at a friend across the room. As you move closer, a pimple on her ear lobe comes into view. As you get closer still, you can no longer tell to whom this pimple-covered ear belongs. As you get closer still, you can see only the pimple, but you have no context that it is attached to an ear or even that it represents a pimple. The ideal arthroscopic depth of field is close enough to visualize the lesion and far enough to have appropriate orientation. Finally, 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 visualization. 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

The following items are needed to perform diagnostic elbow arthroscopy: an arthroscopic camera with color monitor, a 1.9- or 2.4-mm, 30°, short arthroscope with compatible cannula/blunt trocar and light source, lactated Ringer's bags and sterile administration tubing, and photo documentation system. Fluid ingress can be via gravity flow, pressure bag or fluid pump. To perform basic therapeutic elbow arthroscopy, the following instruments are needed: a blunt probe (or "switching stick"), a fine curette, right-angle blunt probe, small graspers, fine-tipped mosquito hemostats, 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.

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 placed in dorsal recumbency with sandbags placed along the edge of the table to function as a fulcrum to distract the medial joint space.

Instrumenting the Elbow

After draping, the assistant abducts the limb firmly against a sandbag or similar fulcrum. Firm pronation of the elbow will further widen the medial joint space (Figure 1). A 3-cc syringe and 22-gauge needle is placed into the joint distal and several millimeters caudal to the medial epicondyle. The needle should pass cleanly into the joint (if the needle must be angled to hit the joint, it should be re-inserted). Joint fluid is aspirated to confirm proper placement (Figure 2). The needle is left in place and lactated Ringer's solution is injected until the joint is distended and pressurized as detected by reverse pressure felt on the plunger (Figure 3). The position of the needle marks the desired location for the arthroscopic portal and the assistant must be careful not to alter the limb position. A #11 blade is advanced as a proximo-distally oriented stab incision though skin and fascia at the level of the needle (Figure 4). As the needle is withdrawn, the arthroscope cannula and blunt trocar are advanced through the stab incision and elbow joint capsule. The trocar is removed from the cannula and fluid should flow freely (Figure 5). The arthroscope is inserted into the cannula and the fluid ingress line is attached. Establishing an outflow (or egress) portal will allow joint lavage to clear the view (Figure 6). 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 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 to 70 mm Hg) 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 (Figure 7).

For probing or treatment of the MCP, an instrument portal is established. First, a 22-gauge needle is passed into the joint at the same proximo-distal level as and ~ 1.5–2.0 cm cranial to the scope. Fluid flow from the needle confirms intra-articular placement, but visualization of the needle at the level of the MCP with the surgeons hands spaced comfortably apart is essential before proceeding (Figure 9). The needle can be used at this time to loosen the fragment from its surrounding attachments, though this may require a stronger probe (Figure 10). A #11 blade is passed into the elbow joint alongside the needle. Next, a mosquito hemostat is passed through the incision into the joint 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 minimized).

MCP Fragment Removal vs. Subtotal Coronoid Ostectomy (SCO)

MCP disease may be present without identifiable fragmentation, thus preoperative computed tomographic (CT) scanning of the elbows can be helpful in the comprehensive evaluation of elbow dysplasia. Blunt probing of the MCP can be helpful in detection of in situ fragmentation. When fragmentation is present, fragment removal can typically be performed with hand instruments (blunt probe, curette, graspers, hemostats, fine osteotome, etc.) and does not require a motorized shaver. Even when fragmentation is present, studies have shown that MCP pathology often extends into the intact MCP adjacent to the gross fragmentation. For this reason, subtotal coronoid ostectomy (SCO) may be indicated in some elbows. SCO can be performed with some combination of a curette, hand- or power-shaver, and osteotome.

Biceps Ulnar Release Procedure (BURP)

The multifactorial pathogenesis of MCP disease is thought to include concussion of the MCP against the radial head. This is theorized to result from strong tensile force of the biceps brachii muscle tendon unit upon its ulnar insertion. Tenotomy of this ulnar insertion via the BURP is one advocated treatment for selected cases of MCP disease. The clinical efficacy of the BURP has not been established to date. A detailed description of the procedure has been published.²

When to Convert to a Medial Mini-Arthrotomy

While arthroscopic surgery of the elbow has distinct advantages, the arthroscopic surgeon must be willing and able to convert the procedure to a mini-arthrotomy in instances when the treatment goals cannot be met arthroscopically. Instances where this conversion from arthroscopy to mini-arthrotomy may arise include hemorrhage or other technical challenge that prevents thorough diagnostic evaluation of the elbow. inability to remove an MCP fragment due to its size, location or other challenges, inability to perform complete BURP tenotomy, inability to safely perform a subtotal coronoid ostectomy (SCO) when indicated SCO has been performed, but the fragment cannot be retrieved arthroscopically.

A thorough understanding of the regional skeletal, muscular, nervous and vascular anatomy is required in order to safely and effectively perform a medial mini-arthrotomy of the elbow joint. Mini-arthrotomy preserves the integrity of the medial collateral ligament.

References

1.  Beale, Hulse, Schulz, Whitney, eds. Small Animal Arthroscopy. Philadelphia, PA: WB Saunders.

2.  Wilson DM, Goh CS, Palmer RH. Arthroscopic biceps ulnar release procedure (BURP): technique descriptions and in vitro assessment of association of visual control and surgeon experience to regional damage and tenotomy completeness. Vet Surg. 2014;43:734–740.