Inflow can be accomplished by gravity or by the use of an arthroscopic pumping device. Gravity inflow is usually adequate when the fluid is introduced through a separate cannula, but may be inadequate if the fluid is introduced through the arthroscope sheath because the flow volume and rate may not be high enough (i.e., using a 1.9-mm arthroscope with a 2.2-mm sheath or with a 2.7-mm arthroscope with a 2.9-mm sheath) to keep up with the evacuation provided by suction instruments such as a shaver system or 2.5-mm suction punch. Using gravity inflow through a dedicated inflow cannula with a 3-mm inner diameter (ID) at a bag height of 3 feet above the joint, a flow rate of 750 mL/min is produced (Fig. 3-1A). In contrast, when using the same cannula and gravity height as above, but with a 2.7-mm arthroscope in the cannula, the flow rate is reduced to 75 mL/min. Using a wider cannula (3.7 mm ID) with the same 2.7-mm arthroscope produces a much higher rate of 500 mL/min (Fig. 3-1B). For comparison, a dedicated 4.5-mm inflow cannula with no scope yields 924 mL/min; a 4-mm arthroscope with a standard 4.5-mm diagnostic (high-flow) cannula yields 110 mL/min. A 4.0-mm arthroscope with a 4.5-mm operative cannula and irrigation extender yields 67 mL/min.

We prefer to inflow through a dedicated 2.9-mm cannula with an infusion adapter (Christmas tree) using a separate portal. It connects to the fluid tubing by a “Christmas tree” (Fig. 3-2A, B).

Several types of arthroscopy fluid management systems are available. They operate through the use of a pumping device or gas to pressurize an irrigating fluid into the joint. All systems
have regulating devices to prevent over- or underdistention, but each works by a different mechanism (Fig. 3-3A, B).

The operating surgeon must exercise extreme caution when using an infusion pump device during arthroscopy. The disadvantages of these systems include mechanical issues, the need for specialized and expensive equipment and tubing, and the need for a team familiar with the operation of the device. Particularly in the foot and ankle, extravasation of fluid could lead to a compartment problem with subsequent disastrous results (Fig. 3-4).

More recently, the rod-lens arthroscope has been produced in 1.9-mm, 2.3-mm, 2.5-mm, and 2.7-mm diameters (Fig. 3-5). These smaller arthroscopes are available in short versions (˜67 mm), having the advantages of a shorter lever arm, excellent picture quality, easy maneuverability, and interchangeable cannulae. The shaft of an arthroscope must be only 67 mm long for use in ankle and foot arthroscopy. However, as the arthroscopes have become smaller and shorter, they have become correspondingly more fragile. Today, the picture quality of the smaller arthroscopes is equivalent to that of the larger versions and is matched to the quality of the latest high-definition or ultra high-definition camera systems.

There are two dimensions to the field of view⁴ (Fig. 3-6). The apparent field of view is the diameter seen at the ocular end of the arthroscope and enhanced by magnification through the video coupler device. The closeness of the arthroscope to the object influences the surgeon’s perception of the field of view. The actual field of view is a measured angle of view the arthroscope produces. This angle varies 90° to 115° for current (wide angle) 4.0-mm arthroscopes. In contrast, the 2.7-mm wide-angle arthroscope has a field of view of 75° to 90°. The term “wide-angle scope” refers to the actual angular field of view rather than the apparent field of view.

The inclination of view is the angle of projection at the objective end (distal) of the arthroscope (Fig. 3-7). The 30°
view, the most practical and the most commonly used, permits excellent visualization within the ankle and foot, particularly when a wide-angle lens is used. The 70° small-joint arthroscope allows the surgeon to see around corners but requires some experience because it is used less commonly. It is particularly helpful in seeing over the medial and lateral domes of the talus, looking into the gutters and evaluating certain osteochondral lesions of the talus and tibia (Fig. 3-8).

Most current arthroscopes have a zero-to-infinity working distance and provide a clear image whether the tissue is close to the lens of the arthroscope or further away. A focusing ring permits fine adjustment to the picture quality. Once the focus is set, rarely are adjustments necessary.

A careful diagnostic examination is a composite of multiple images obtained by moving the arthroscope in different positions and using the arthroscope’s rotation ability and angle of inclination.

The arthroscope is introduced into the joint by means of a cannula or sheath, which should be 1 to 2 mm shorter than the arthroscope when fully engaged. The tip of the cannula is angled in a manner to accommodate the angle of the scope lens. The proximal end of the sheath should have a quick and secure connecting mechanism to accept a trochar or arthroscope. This allows easy insertion and removal of the arthroscope from the sheath during
surgery. Sheaths are available with and without side ports for fluid flow or suction (Fig. 3-9). The amount of fluid that can be introduced through the sheath depends on the size of the sheath and the pressure applied to the fluid (see Fig. 3-1).

The arthroscopic sheaths should be interchangeable so that the arthroscope and instruments (shaver blades) can be easily placed through any of the portals desired without repeated instrumentation and subsequent soft tissue trauma. “Switching sticks” that are smaller in diameter than the cannulae being used should also be available and are particularly useful if the cannula comes out of the joint inadvertently or if the surgeon needs to switch from a cannula with a side port to one without. For systems without interchangeable cannulae, plastic disposable cannulae can be used to allow exchanges of instruments through a given portal. However, the small size of the foot and ankle joints does not lend itself well to the use of small disposable cannulae.

Noninvasive techniques include manual distraction and gravity distraction, which are “uncontrolled” methods. Although these methods require no specific equipment, they are often inadequate for complete visualization and operative arthroscopy. Other noninvasive methods, such as the modified clove-hitch knot around the ankle, can be termed “semicontrolled”⁵ (see Figs. 1-20 and 3-11). This method is inexpensive but may be inadequate for good distraction; also, the degree of force and the duration of distraction are hard to monitor. The third type of noninvasive distraction, termed “controlled,” involves the use of prefabricated sterile straps that hook around the front of the foot and the back of the heel and are attached to an outrigger device in which a distraction force is generated (Fig. 3-12A). Countertraction is applied by a nonsterile thigh support (Fig. 3-12B, discussed later).

A fracture table can also perform this type of distraction, but it is not necessary with today’s soft tissue distraction devices. Other devices are available that allow this type of distraction while the patient’s knee is bent at 90°.

Some of these devices permit the amount of pressure and force to be monitored and maintained mechanically. Presently, this is the most common type of distraction used for foot and ankle arthroscopy.

Invasive distractors use pins in the tibia and talus or calcaneus to provide mechanical distraction. A “controlled” system usually has a strain gauge to measure the amount of force and permit some degree of freedom within the
ankle joint (Fig. 3-13A). The disadvantages of these systems include the need to insert pins and the risk of damage to the neurovascular structures, infection, and fracture. However, they allow large amounts of distraction force to be applied across the joint in a controlled manner. In the past, a “multimode” distraction system (Acufex) was developed to allow both invasive and noninvasive distraction to be applied through the same device.⁶ This apparatus allowed the surgeon to start with a noninvasive technique and progress to invasive techniques only if adequate distraction and visualization were not obtained (see Fig. 3-13B). Presently, invasive distraction is rarely used.

We use a noninvasive distraction device with a disposable strap on every ankle and subtalar arthroscopy.

The patient is usually done under general anesthesia with a popliteal block. The patient is “paralyzed” to increase distraction. Maximum distraction is initially applied, and over time more distraction can be obtained. Maximum distraction is done for no more than 1 hour, and then the distractor is clicked back (or relaxed) one notch. This maneuver is also helpful to relax the anterior capsule and see the anterior distal tibia and medial and lateral gutters more easily.

In the great toe and lesser toes, noninvasive distraction is performed in a semicontrolled manner using a toe trap attached to a rope-and-pulley system. This is discussed
further in Chapter 16. Some type of distraction is required in most arthroscopy cases of the foot and ankle.

Contraindications to the use of noninvasive distraction include impaired circulatory status, diabetes, certain generalized medical conditions, and ankle edema or fragile skin conditions. Invasive skeletal distraction is contraindicated with localized or generalized infection, osteopenia, open physis, ligamentous laxity, and active reflex sympathetic dystrophy and in high-performance athletes who must return to their sport quickly.

Formats are the manner in which electronic signals produced by a camera carry their color and brightness information to an accessory device for display or manipulation. Analogs (composite, Y-C [S-VHS], RGB, and HD [HD-SDI, HD-DVI, and YPrPb]) are terms describing various video formats.