chapter 5: Arthroscopy of the patellofemoral joint
BASIC SETUP AND TECHNIQUE
When the primary area of interest is the patellofemoral joint, the patient is in the supine position, with the end of the operating table flat. After the anesthetic is administered, a tourniquet is placed high around the proximal thigh and covered distally with an adhesive drape to prevent sliding during the surgery. If the tourniquet is placed too distal on the femur, the proximal patellar portals will be difficult to use, because the arthroscope will lever on the tourniquet and prevent adequate mobility. The standard arthroscopy leg holder that fits around the tourniquet is too bulky and is not used.
The patient's knee is prepped and draped, and a post is placed next to the knee in the down position for later use if needed. This basic setup allows the surgeon to do the patellofemoral arthroscopy with the knee extended, yet allows for the knee to be flexed off the table later for examination of the notch and other compartments. When the time arises to examine the rest of the knee joint, a circulatory nurse or assistant in the room will raise the post on the side of the table that allows the surgeon to apply a valgus force in order to look medially. The standard "figure 4" position can be used to look laterally. The unaffected leg is padded and secured to the table.
We routinely begin our diagnostic arthroscopy of the patellofemoral joint with the superomedial portal described by Schreiber (8). This portal may be more comfortable to use if the surgeon stands on the opposite side of the table for this part of the case. The monitor is at the head of the table on the affected side. If the primary area of interest is going to be the patellofemoral joint, we start with the end of the table flat. The portal is made two to three fingerbreadths above the patella just medial to the midline. The larger the leg, the more proximal the starting point (it is unusual to need to start more than three fingerbreadths proximal to the patella). This keeps the scope out of the thick quadriceps tendon and will allow a good view of the patellofemoral joint (Fig. 5.1). A No. 11 scalpel blade is used to make a longitudinal incision at the angle you want the cannula to enter the suprapatellar pouch and is carried down through the skin only.. We find that angling the arthroscope 60 degrees off the horizontal works well, entering the suprapatellar pouch 2 cm above the patella, and then the scope may be flattened once the cannula is in place (Fig. 5.2). This makes a shorter distance from skin to joint and still allows a flatter angle to be obtained once the scope is inserted. If you allow the arthroscope to enter the suprapatellar pouch too close to the proximal border of the patella, this area is difficult to visualize.
After the incision is made, follow the same course with your blunt trochar. The superomedial aspect of the trochlea may be more prominent from the anterior view than from the lateral (9), and you will often feel your trochar contact this area, preventing you from entering the joint. By redirecting your hand slightly to the lateral (thus, the tip of the trochar medially), you may enter the joint by getting the trochar to slide down the medial gutter. Another option is to slightly raise the tip of the trochar to get up over the lip and gently advance into the joint. Care must be taken not to score the articular cartilage with the trochar.
Once the cannula and arthroscope are in the knee joint, the fluid may be attached to the cannula, or a separate portal may be made for inflow. Inferolateral or inferomedial portals are established under direct vision.. Keep in mind when making these working portals that they will be used later for the arthroscope to view the remainder of the joint, so place them in an appropriate position, usually approximately 5 to 10 mm distal to the patella. The easiest way to establish working portals is to use a spinal needle as a guide, and make sure the needle can reach the area of interest before making your incision.
From the superomedial portal, you are able to visualize the patella, trochlea, fat pad, anterior horns of the menisci, plicae, medial and lateral gutters, a portion of the anterior cruciate ligament, and ligamentum mucosum. From this proximal view, you may easily watch the patella track in varying degrees of flexion. The patella will begin to engage the trochlea at 10 to 20 degrees of flexion and should be centered in the trochlea without tilt by 45 degrees (Figs. 5.3 and 5.4). The pump should be at no more than 60 mm Hg pressure during this maneuver to allow the patella to engage and center in the trochlea more physiologically. As you watch the patella enter the trochlea, try and identify causes of articular lesions. For example, chronic lateral tilt viewed arthroscopically may reveal "kissing lesions" on the far lateral trochlea and the central ridge or lateral facet of the patella, because these two areas may be receiving the most contact (10). Patients with a history of patellar dislocation, however, may have lateral trochlea and medial facet lesions (Fig. 5.5), because the medial patella facet is frequently damaged at the time of patella relocation after the dislocation. Patients who have a history of a dashboard type injury, where the patellofemoral joint takes the brunt of injury, may be seen with specific lesions. Proximal pole lesions of the patella are common in these types of patients (Fig. 5.6). There may also be concomitant damage of the trochlea from these injuries; a Merchant view is sometimes helpful in delineating these lesions (Fig. 5.7) (11). Place a hook probe through the inferolateral portal and palpate the articular surfaces of the patella and trochlea. Record the size, depth, and location of any lesion(s). Articular cartilage is usually firm on palpation. Your probe should not do more than slightly dimple the cartilage with mild pressure (Fig. 5.8).
After the diagnostic portion of the arthroscopy, one may then debride loose articular lesions using a curved shaver through one of the working portals. Remove only loose cartilage and do not bevel the edges, because you will be damaging normal articular cartilage. You may also drill or abrade exposed bone (Fig. 5.9). Recently, straight and angled picks have been available to arthroscopically create small holes in the exposed subchondral bone to create bleeding that will allow fibrocartilage to form in the defect. These are technically easier to use, than a drill and do not cause the significant increase in local tissue temperature of a drill.
After this is accomplished, move your arthroscope into the inferolateral portal and complete the arthroscopy. More information may be obtained about the patellofemoral joint if it is viewed from two directions. From this inferior portal, the proximal one third of the patella and suprapatellar pouch are better visualized. You may use the inferomedial portal as your working portal if additional debridement is necessary. You may also work through your superomedial portal, but you need to keep a cannula in the portal, because it is difficult to get in and out due to the thickness of soft tissue. Also, repeated trauma to the quadriceps by repeated entry is not advisable. The remainder of the knee joint should be inspected at this time to rule out concomitant diagnoses. The post at the side of the table should be raised to aid in applying a valgus force to look medially. Although the central approach is excellent (12) for visualizing other areas of the knee, this central portal is not ideal for viewing the patellofemoral joint.
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