Arthroscopic Knot Tying

Published on 11/03/2015 by admin

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CHAPTER 5 Arthroscopic Knot Tying

The last 2 decades have been a period of dynamic and exciting growth in the field of reconstructive arthroscopy. The drive of patient demand, availability of improved instrumentation and implants, and increasing acceptance of arthroscopic reconstructive techniques by the orthopedic community have all fueled development of increasingly complex arthroscopic reconstructive surgical procedures. The ability to approximate tissue with confidence is a cornerstone of complex arthroscopic procedures and integral to this advancement has been the evolution of arthroscopic knot tying. Unfortunately, development of arthroscopic knot tying skills has proven a stumbling block to many arthroscopists because arthroscopic knot tying is not as intuitive as open knot tying. Recognizing this frustration, many device and implant manufacturers and a number of innovative orthopedic surgeons have devised ways whereby an orthopedist can accomplish some of these reconstructive techniques without the need for tying knots arthroscopically.¹^–⁸ These techniques are, by their nature, dependent on a particular piece of equipment or implant, which subject to the same risk of failure at the time of surgery as any other implant or device. Thus, although these techniques may allow a surgeon to bypass knot tying in some cases, the prudent orthopedist would not undertake a complex arthroscopic reconstructive procedure that relies on tissue fixation without the ability to accomplish basic arthroscopic knot tying as a backup plan. Perhaps more importantly, the ability to tie knots arthroscopically also gives the reconstructive arthroscopist freedom to tailor specific reconstructions to the needs of the patient without being constrained by those options allowed by knotless devices.

LEARNING TO TIE KNOTS ARTHROSCOPICALLY

Expertise in arthroscopic knot tying can be gained by memorization of a few basic knot patterns, development of a sound understanding of the path of the suture within the joint, and the practice of basic motor skills with the knot pusher. Many suture anchor and arthroscopic instrumentation manufacturers make arthroscopic knot-tying practice boards available for instruction. These knot-tying boards are an excellent way to gain experience with conditions that mimic those encountered when sewing tissue within joints. The boards typically allow the surgeon to tie through a cannula and to approximate rubber tubing that simulates tissue under tension. They have the added convenience of being available for use at any time of day, for any amount of time, and typically at no cost to the surgeon.

The quickest and most certain way to learn arthroscopic knot tying is to attend hands-on instructional courses such as the Master’s Series courses presented by the Arthroscopy Association of North America (www.aana.org). These 3-day courses, offered throughout the year, provide sustained knot tying instruction in both didactic and laboratory formats. In the laboratory setting, experienced surgeons are available to assist and troubleshoot the student’s knot tying as dexterity is achieved.

DEFINITIONS

As we begin the discussion of arthroscopic knot tying, a few commonly encountered terms merit definition:

▪ Knot security—the ability of the overall knot to resist slippage when a load is applied ⁹

▪ Limb—a free suture end

▪ Loop security—the ability of a knot to achieve and maintain tightness in the initial knot loop that approximates the tissue ⁹

▪ Post limb—the limb around which loops are being passed at any given time when building the knot (the limb acting as the post is typically alternated in various patterns during knot tying to make the knot more secure)

▪ Wrapping limb—the suture being passed around the post limb at any given time

INSTRUMENTATION FOR ARTHROSCOPIC KNOT TYING

Several basic instruments, both disposable and reusable, as well as preferred suture material are routinely needed for arthroscopic knot tying. The surgeon must ensure that these items are readily available before undertaking any procedure that will require arthroscopic knot tying.

Cannulas

The use of cannulas for arthroscopic knot tying helps minimize entanglement of soft tissue in the knot, one of the primary stumbling blocks in arthroscopic knot tying. By passing the knot through the smooth lumen of a cannula instead of directly through muscle fibers and other soft tissue while entering the joint, soft tissue that might become entangled within the knot is effectively bypassed.

Many manufacturers offer disposable cannulas made of clear plastic. These clear cannulas allow the surgeon to see the knot as it is advanced into the joint, which can be a great help in understanding and visualizing the knot seat properly, and any inadvertent twisting or tangling.

Cannulas with threads or blunt spikes on their outer barrel are also commonly available. These features help minimize the tendency of the cannula to slip out of the portal, effectively linking the cannula to the joint wall as instruments are passed in and out during lengthy or complex procedures in which soft tissue swelling can affect portal placement. An additional benefit of this fixation between the cannula and joint wall is that when the cannula is drawn away from the operative field by applying an outward pull, the joint wall is also drawn away from the operative field. This increases space for visualization, which can be a great benefit when visualization is otherwise suboptimal.

Another characteristic that varies among different cannulas is the degree of flexibility of the cannula itself. Flexible cannulas can deform slightly to allow passage of an instrument that would otherwise require a larger diameter cannula. This allows use of smaller cannulas in many cases while still allowing passage of full-sized instruments.

Sutures

The arthroscopic surgeon has a rich variety of sutures from which to choose. They offer great variation in material qualities such as strength, surface texture, resistance to fraying, and permanence. The ideal suture would provide secure fixation with a minimally bulky knot, have excellent resistance to mechanical abrasion, provide minimal resistance when the knot is being advanced, and provide excellent resistance to knot retreat or loosening. Suture of at least 27 inches in length is needed for effective use of most knot pushers. For a dual-lumen single-hole knot pusher, a minimum suture length of 36 inches is required.

The decision between dissolving (e.g., PDS II, Ethicon, Somerville, NJ) and permanent (e.g., Ethibond Excel, Ethicon) suture depends both on surgeon preference and situation-specific factors such as the nature of the reconstruction and the particular tissue being approximated in the process of that reconstruction. Historically, monofilament suture has been easier to pass with available arthroscopic suturing instruments but in general is more difficult to tie securely,¹⁰^–¹² presumably because of differences in surface characteristics of the two types of suture.

A new class of high-strength braided suture incorporating ultra–high-molecular-weight polyethylene (UHMWPE) has recently become available. These sutures, including FiberWire (Arthrex, Naples, Fla), Orthocord (DePuy-Mitek, Raynham, Mass), Hi-Fi (ConMed Linvatec, Largo, Fla), Ultrabraid (Smith & Nephew, Andover, Mass), Force Fiber (Stryker Endoscopy, San Jose, Calif), MagnumWire (ArthroCare, Sunnyvale, Calif) and MaxBraid PE (Biomet, Warsaw, Ind), have been shown to have improved mechanical properties compared with traditional suture materials, but have also been shown to have different knot security qualities.¹³^–¹⁷ These differences in knot security qualities, presumably caused by differences in surface properties, mandate the need for additional half-hitches to lock these knots. One recent study has demonstrated that a total of four locking half-hitches backing a sliding arthroscopic knot is not enough to prevent knot slippage reliably with these high-strength sutures.¹⁷ The authors did not give a recommendation regarding the appropriate number of locking half-hitches needed. Other investigators have suggested that the addition of two locking half-hitches beyond the number that would be used to secure more traditional suture materials is sufficient for reliable knot security.¹⁴

Some of the newer high-strength sutures provide greater bulk than the same knots tied with traditional sutures.¹³ Selecting a knot with a lower profile may be very important when using newer high-strength sutures. The surgeon should also be aware that damage to gloves and even finger skin tears can be sustained when tying vigorously with these high-strength suture materials.¹⁸ Moderation of vigor when tying any knot is sensible, especially when tensioning the tissue loop to avoid tissue strangulation.

Suture Retrievers

Sutures can be manipulated and retrieved arthroscopically with a number of commonly available instruments. A simple nonspecific arthroscopic grasper with teeth can be used, but may fray and thereby weaken the suture being manipulated. A variety of graspers designed specifically for suture or rotator cuff manipulation are now available. These typically have smooth, atraumatic jaws that allow manipulation of the suture without damage and the suture slides within the instrument as the instrument is drawn out of the joint. This provision for suture movement within the jaws of the device reduces trauma to the tissue from the sawing effect of the suture sliding through the target tissue.

Knot Pushers

Several different knot pusher designs are available to the arthroscopic surgeon—single-hole, double-hole slotted, mechanical spreading, and dual-lumen single-hole. Single-hole knot pushers are the most commonly used type because they can easily push a knot down by placement on the post limb, or pull a loop down by placement on the wrapping limb. Double-hole knot pushers can be used for these tasks as well, but their added size and bulk confer no advantage and can complicate passage of individual knot loops. Double-hole knot pushers find their main use in correcting twists of the suture limbs prior to knot tying. Both suture limbs are threaded through the knot pusher and the pusher is advanced to the target tissue intra-articularly. Any twist of the sutures is immediately evident and can be corrected with a simple clockwise or counterclockwise turn of the knot pusher as both limbs are captive in the tip of the knot pusher. Slotted knot pushers function similarly to single-hole knot pushers, but allow the knot pusher to be applied and removed from the suture strand without having to withdraw the knot pusher from the joint. This capability can be a liability, however, if the knot pusher is inadvertently separated from the intended suture limb during the process of tying. The incomplete loop of the knot pusher tip also opens the door for soft tissue entanglement. The dual-lumen single-hole knot pusher is designed to hold tension in that portion of the knot already passed while additional throws are tied and advanced. Investigation has shown this knot pusher design to be very effective in achieving loop security during arthroscopic knot tying.¹⁹ This knot pusher does however represent a per-use cost (it is disposable), requires use of longer sutures (36 instead of 27 inches), and may require a greater degree of technical proficiency. The dual-lumen single-hole knot pusher is most useful when the surgeon has to tie a nonsliding knot. These nonsliding knots do not have a sliding component to hold temporary tension in the initial (tissue) loop while additional securing throws are being passed. By virtue of its design, the dual-lumen single-hole knot pusher provides this tension, and therefore good loop security, even with simple half-hitch–based nonsliding knots.

In summary, a single-hole knot pusher is a good choice for a primary knot pusher because it has the greatest overall utility for passage and tensioning of knot loops. A double-hole knot pusher has the quickest ability to detect and correct suture twisting prior to tying and is a great adjunct to a single-hole knot pusher. A dual-lumen single-hole knot pusher is used primarily when tying nonsliding knots.

TIPS AND TRICKS FOR INSTRUMENTATION

Cannulas

The use of cannulas helps significantly in preventing soft tissue interposition and entanglement. Drawing the suture limbs out through the cannula immediately prior to tying is a simple way to ensure that no soft tissue bridge intervenes between the suture limbs. Such a soft tissue bridge between the two limbs would make subsequent knot passage impossible. Use of a cannula for the actual tying process also dramatically reduces likelihood of soft tissue entanglement. The tip of a cannula used for knot tying should be directed to the target tissue by the assistant to facilitate knot and instrument passage and to lessen the risks of soft tissue entanglement and suture fraying from the edge of the cannula if pointed elsewhere.

Suture Anchors

Overpenetration of suture anchors into bone should be avoided because this recesses the suture eyelet relative to the cortical surface, potentially leading to abrasion of the suture on the edge of the suture anchor tunnel as the suture exits the tunnel. This can lead to suture failure. For anchors with fixed (nonsuture) eyelets, the eyelet should be aligned when sinking the anchor so that the suture path is aligned with knot tying (Fig. 5-1).

FIGURE 5-1 Suture anchor placed incorrectly (top) and correctly (bottom).

Sutures

Prior to tying each suture, the surgeon should quickly assess whether the suture slides. If the suture moves at least relatively freely, a sliding arthroscopic knot backed with alternating post half-hitches gives the best combinations of tissue approximation and ease of tying. If the suture does not slide freely, a non-sliding knot must be tied. Sliding the knot through soft tissue requires a deft touch because an overly aggressive back and forth motion can damage the soft tissue being repaired.

Occasionally, fraying of the suture is recognized after suture passage but prior to knot tying. This situation presents two options—replace the suture with an intact suture, or carefully tie the damaged suture.

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