CHAPTER 4 Diagnostic Arthroscopy for the Ankle and Subtalar Joints

The ankle is a highly constrained joint composed of complex, curved articular surfaces that are stabilized by ligaments with various degrees of laxity. These anatomic constraints make arthroscopy of the ankle joint more difficult than in larger joints such as the knee and shoulder. Early attempts to perform arthroscopy of the ankle joint were met with various degrees of success. In a 1931 cadaver study, Burman suggested that the ankle joint “… is not suitable for arthroscopy.”¹

Arthroscopists in the 1980s began to apply modern techniques to instrumentation of the ankle and defined the basic portals with which to approach the joint.^2–4 Since then, two technical advances have facilitated routine performance of ankle arthroscopy for diagnosis and surgical procedures. First, the development of high-quality, small-diameter arthroscopes has allowed instrumentation of the ankle with increased ability to visualize the entire joint while decreasing the likelihood of iatrogenic articular cartilage injury. Second, techniques have been developed for noninvasive joint distraction to facilitate instrument passage and decrease joint injury.⁵ Without distraction, it is often impossible to visualize the central and posterior compartments of the joint from the anterior portals. Early attempts to distract the joint used pins placed into the tibia and calcaneus that were connected to a distractor device similar to an external fixator. The use of these devices was associated with significant complications, including pin tract infection and neurovascular injury.⁶ Elimination of these complications while effectively distracting the joint with noninvasive strap distraction is a major advantage, and invasive ankle joint distraction is no longer recommended.

PATIENT POSITIONING

The patient is placed supine on the operating table with the hip and knee flexed and supported by a well-padded leg holder (Fig. 4-1). I prefer a leg holder with a long thigh segment and short knee segment to diffuse the distraction force over the wide area of the thigh rather than concentrating the force in the popliteal space and potentially causing obstruction to venous outflow. Sterile drapes are applied after skin preparation.

FIGURE 4-1 Position for ankle arthroscopy. The patient is supine, and the hip and knee are supported by a well-padded leg holder. The leg holder has a broad thigh support so that as distraction force is applied to the ankle, it is dissipated over a wide area of the thigh rather than concentrated in the popliteal fossa.

A sterile clamp is attached to the operating table side rail over the sheets, and a bar is fixed to the clamp. The noninvasive ankle distractor strap is placed around the hindfoot and midfoot and connected to the bar using a segment of sterile two-sided Velcro. This distraction setup allows the ankle and foot to rest in a plantigrade position while retaining the ability to move the ankle in dorsiflexion and plantar flexion intraoperatively (Fig. 4-2).

FIGURE 4-2 The leg is prepared and draped with sterile sheets, and the noninvasive distractor is applied to the ankle. The strap that is placed around the hindfoot and midfoot is attached to the bar using a strip of Velcro, with which the distraction force can be varied.

Invasive distraction is not required for standard ankle arthroscopy. It poses unnecessary risks to neurovascular structures, along with risks of infection and stress fracture.

Anatomic landmarks are then marked with a sterile marking pen. I outline the medial malleolus and the anterior joint line along with the contour of the distal fibula. Also marked are the position of the tibialis anterior tendon medially, the peroneus tertius tendon laterally, and the lateral border of the Achilles tendon posteriorly. The position of the superficial peroneal nerve branch passing over the anterolateral ankle can often be appreciated by plantar flexing and inverting the ankle.

PEARLS& PITFALLS

PEARLS

• Noninvasive ankle distraction assists in exposure of the entire ankle joint for arthroscopy.

• Small joint arthroscopes with a 2.7-mm diameter and with 30- and 70-degree viewing angles provide the best visualization.

PORTAL CREATION

Careful attention to portal creation technique can minimize the incidence of iatrogenic injury to neurovascular structures. The nick and spread technique is advised. Each portal is created by incising only the skin, avoiding penetration of the subcutaneous tissues with the knife blade. A small hemostat clamp is used to spread the subcutaneous tissues down to the level of the capsule. The capsule is penetrated using a blunt trocar to minimize the risk of iatrogenic articular cartilage injury.

The three standard working portals for ankle arthroscopy are the anteromedial portal, the anterolateral portal, and the posterolateral portal (Fig. 4-3). The anterocentral portal was used in the early days of ankle arthroscopy because of the purported benefit of increased visualization in the central compartment. However, this portal placement poses significant risk of injury to the deep peroneal nerve and the dorsalis pedis artery. The use of small joint arthroscopes and noninvasive joint distraction obviates the use of this portal for ankle arthroscopy.

FIGURE 4-3 Sketch showing the anatomy of the ankle in relation to the standard portals. A, The anteromedial portal is located immediately adjacent to the medial border of the tibialis anterior tendon at the level of the joint line. The anterolateral portal is located lateral to the lateral border or the peroneus tertius tendon. Accessory medial or lateral portals may be placed to approach the particular pathology found at surgery, and the location is guided using an 18-gauge needle intraoperatively. B, Posterolateral and posteromedial portal positions are shown in relation to significant anatomic structures.

The first portal created should be the anteromedial portal. In most patients, there is an indentation in the anteromedial articular surface of the distal tibia, known as the notch of Harty, that facilitates passage of instruments across the ankle joint from medial to lateral aspects. The surgeon palpates the tibialis anterior tendon and inserts an 18-gauge needle into the joint immediately adjacent to the tendon’s medial border (Fig. 4-4). As the needle enters the joint, the surgeon notices the sound of air entering the joint, which also allows the ankle to be distracted more easily. Needle placement is adjusted proximally or distally until the position that allows easiest passage across the joint is identified as the optimal location for the portal. The cannula is introduced through this portal, and the 2.7-mm arthroscope is introduced into the joint.

FIGURE 4-4 Each portal is located using an 18-gauge needle to determine the optimal position that allows easy passage of the instruments across the joint.

With the arthroscope in the anteromedial portal, the posterolateral portal is created under direct visualization. The portal is located adjacent to the lateral border of the Achilles tendon and approximately 1 to 2 cm distal to the anterior portal so that an upwardly angled 18-gauge needle passes into the joint beneath the posterior syndesmotic ligament complex and accommodates the posterior curvature of the talar dome (Fig. 4-5). Another 2.7-mm cannula is placed and functions as a dedicated inflow cannula attached to an arthroscopic fluid pump.

FIGURE 4-5 A, Intraoperative photograph shows the relative position of the posterolateral portal to the anterior portal. The posterolateral portal is approximately 1 to 2 cm distal to the level of the anterior portals and angled upward to accommodate the curvature of the talar dome. B, Cross-sectional sketch shows the anatomy of the ankle joint, which dictates the angle at which the posterior portal must be placed to accommodate the curvature of the talar dome.

Although inflow can be performed by gravity, the arthroscopic pump allows control over the inflow pressure and the maximum flow rate allowed by the pump. The surgeon must monitor the condition of the soft tissue of the calf frequently during the case to ensure that fluid extravasation does not result in excessive swelling.

The anterolateral portal is placed in a manner similar to placement of the anteromedial portal adjacent to the lateral border of the peroneus tertius. Careful attention to portal creation technique minimizes the risk of injury to branches of the superficial peroneal nerve, the most commonly injured nerve in ankle arthroscopy, which is always located close to the anterolateral portal. The arthroscopic view is directed laterally to visualize entry of the 18-gauge needle, ensuring optimal position as the needle is passed across the joint.

Accessory portals medially or laterally may be required in some circumstances, particularly if surgery is being performed deep in the medial or lateral gutters. Optimal location for these portals is identified using a needle, and as long as there is approximately 1 cm between the standard portal and the accessory portal, wound-healing problems should be minimal. The trans-Achilles tendon portal described in the early days of ankle arthroscopy is not necessary and poses unnecessary risks of injury to the tendon.

PEARLS& PITFALLS

PEARLS

1. The medial portal should be made as close as possible to the medial border of the tibialis anterior tendon without injuring the tendon. The closer the portal deviates toward the medial malleolus, the more difficult arthroscope maneuverability will be.

2. An 18-gauge needle is used to precisely localize the position of the portal.

3. When creating each portal, the skin is incised for a distance of 4 to 5 mm (i.e., larger than the outer diameter of the arthroscope’s sheath). This technique allows easy instrument passage while minimizing soft tissue trauma during multiple passes through the portal.

PITFALLS

• Avoid injury to superficial neurovascular structures using the nick and spread technique for portal creation:

1. Incise only the skin with a no. 11 blade.

2. Spread subcutaneous tissue with mosquito forceps.

3. Penetrate the joint capsule with a blunt trocar.

• Avoid portal complications such as sinus formation:

1. Make the portal large enough to easily pass instruments without causing soft tissue damage.

2. Use simple sutures at the conclusion of the case.

3. Impose a brief period of postoperative immobilization (about 1 week) in a splint to allow soft tissue healing.