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.

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.

If the surgeon wishes to replace a braided suture, the replacement suture is threaded onto a thin free needle and the free needle is used to pierce the damaged suture a few centimeters from its end. The damaged suture is pulled retrograde through the tissue and/or anchor, drawing with it the new intact suture. The damaged suture is then pulled from the intact suture and discarded. To replace monofilament suture, place the ends of the injured and intact sutures side by side and tie a tight simple stitch with both strands. The damaged suture is then pulled retrograde through the tissue and/or anchor and the damaged suture is cut free and discarded.

If the surgeon wishes instead to continue tying a damaged suture, the suture is purposely shifted to ensure that when the tied knot is seated, the damaged area of the suture does not end up in the final knot. This requires understanding of the direction and degree of shift anticipated as the sliding knot is seated. Tying of a damaged high-strength suture is generally possible without gross failure. Tying of damaged common (regular strength) suture can occasionally result in breakage when the knot loops are tensioned. If the suture breaks prior to completion of the locking half-hitches, the surgeon is in the difficult position of assessing whether the number of successfully thrown locking half-hitches is satisfactory or whether the suture needs to be replaced. One possible option in this predicament is to use an arthroscopic tissue grasper on the broken limb intra-articularly and then use this grasper–suture stump composite as the limb for subsequent throws.²⁰

Passing only the two suture limbs being tied through the working cannula dramatically reduces the likelihood of suture tangling and speeds knot tying significantly. Other sutures within the joint are best passed from the joint through another portal (Fig. 5-2). These other sutures can be passed out of the joint through the same portal by placing them between the working cannula and portal wall. This can make subsequent retrieval of the sutures difficult. Friction between the portal wall and cannula makes it difficult for the tissue to slide while being retrieved. Binding of the suture against the end of the cannula along with the need to apply greater force increases the likelihood of suture stretching or fraying (Fig. 5-3).

FIGURE 5-2 Extra sutures drawn away from operative field through accessory cannula.

FIGURE 5-3 Suture binding against tip of cannula caused by excess tension and sharp edge.

Once the suture limbs are passed out through the cannula and separated, placing a finger between the suture limbs (Fig. 5-4) separates them, making it easier to differentiate the limbs when constructing the knot. It also prevents twisting of the limbs within the cannula as the initial knot is constructed.

FIGURE 5-4 Assistant’s finger placed to maintain suture separation and orientation, facilitating knot tying.

In choosing the limb to act as the post, select the limb that exits the tissue where you want the knot bulk to seat. With a typical capsulorrhaphy, the limb on the capsular side would be the appropriate choice for the limb post²¹ so as to keep the knot away from the joint surfaces. Serious and lasting complications have been reported when bulky arthroscopic knots are placed too close to articular surfaces.^22,23

When first learning to tie arthroscopic knots, it is helpful to apply a hemostat to the end of the post limb to remember which limb is serving as the post at any given time. One other helpful practice is to make a habit of holding the two suture limbs separated between the thumb and middle finger of the nondominant hand, instead of the thumb and index finger, which may feel more natural (Fig. 5-5A). Using the middle finger for this grasp leaves the index finger free to help with wrapping and manipulation of the wrapping post during knot tying. This can significantly facilitate knot tying once the surgeon becomes accustomed to the sequence.

FIGURE 5-5 Tennessee slider knot. A, First overhand throw. B, Passage of suture to complete sliding knot. C, Completed sliding knot. D, Compacting sliding knot. E, Traction applied to post, drawing knot into joint to target. F, First locking half-hitch (underhand). G, Past pointing to apply tension to locking loop. H, Post switched, applying second locking half-hitch (overhand). I, Past pointing to apply tension to locking loop. J, Post switched, applying third locking half-hitch (underhand). K, Past pointing to apply tension to locking loop.

Suture Retrieving

If there are multiple suture pairs within the joint, determine the path least likely to lead to entanglement of the knot as knot tying proceeds. Pass a suture retriever into the cannula and trace the desired path until you reach the target sutures. Grasp both sutures to be tied at once, and draw them out of the cannula. This ensures that no suture strand or tissue intervenes between the two suture limbs of your planned knot.

Knot Pushers

To untwist sutures, thread both suture limbs through a double-hole knot pusher and advance the knot pusher into the joint while you view the end of the cannula with the arthroscope. If a twist in the suture limbs appears, “untwist” the suture limbs by rotating the knot pusher. Pull the knot pusher straight out of the cannula in that rotated position and grasp the sutures between the knot pusher and cannula. Separate the sutures to opposite sides of the cannula in the direction they exit the cannula and proceed with knot tying.

If a double-hole knot pusher is not available, pass a single-hole knot pusher down one limb of the suture and check for suture twisting, as noted. If twisting is noted, pass the tip of the knot pusher around the other limb in the direction needed to untwist the knot. Once untangled, hold the tip of the knot pusher as far as possible to the side of the cannula and withdraw it. Capture and separate the sutures between the knot pusher and cannula as described earlier for the two-hole knot pusher technique. Another option is to grasp one suture limb from a separate portal, thereby untangling the sutures, and then regrasp the suture from the working cannula.

Many surgeons new to arthroscopic knot tying struggle in understanding how best to use the two hands during knot tying. Think of the two suture limbs as being two completely separate entities, with very different tasks. By extension, think of your two hands in the same way to the extent that they each handle one of the two suture limbs. The post limb is the passive limb. All that is needed for the post is to maintain steady tension—initially to seat the sliding knot and subsequently to prevent retreat or loosening of the sliding knot. The hand controlling the post is therefore the passive hand, and its job is simply to maintain that tension regardless of whatever else is happening in the case. If you can make this differentiation, you will see a marked improvement in your knot-tying skills.

For subsequent throws of both sliding and nonsliding knots, the knot pusher is applied to the wrapping limb and loops are pulled down to the target. To create as much internal friction as possible, the post is alternated when tying the knot. The knot pusher has to be transferred from limb to limb during application of subsequent throws. Pulling subsequent loops (by having the knot pusher on the wrapping limb) instead of pushing them (with the knot pusher on the post limb) allows past pointing to tighten the knot. Past pointing is simply the process of pulling the loop being tied beyond the knot to establish a secure configuration (see Fig. 5-5G). This is the same motion one would use when tying an open knot to cinch the knot.

Types of Knots

Arthroscopic knots fall into several general classes—nonsliding, sliding, and sliding-locking.

Choosing an Arthroscopic Knot

For typical arthroscopic reconstructive purposes, a sliding knot provides the best loop security, reproducibility, and greatest ease of tying. Based on the prevalence of braided sutures in commercially available implants and on the better knot security afforded, braided permanent suture is the suture material most commonly used. The surgeons preference is the primary consideration in the decision of a sliding versus a sliding-locking knot. Either type should be backed with alternating post half-hitches to achieve adequate knot security.^{10,12,17,24,26,29}

In terms of specific knots, studies have indicated that when tied with high-strength sutures, the Tennessee slider³³ (sliding knot), SMC knot²⁷ (sliding-locking knot), and Revo³³ knot (nonsliding knot) are the best for knot security.¹⁷

Knot-Tying Mechanics

Tying Arthroscopic Knots

FIGURE 5-6 SMC knot. A, First steps of sliding knot. B, Completion of sliding knot. C, Traction applied to post, drawing knot into joint to target. D, Traction applied to wrapping limb while knot held in place with pusher on post, locking knot.

FIGURE 5-7 Revo knot. A, First half-hitch (underhand). B, Past pointing to apply tension to loop. C, Second half-hitch (underhand); past pointing as in B. D, Third half-hitch (overhand); past pointing as in B. E, Post switched, applying fourth half-hitch (underhand); past pointing as in B. F, Post switched, applying fifth half-hitch (underhand); past pointing as in B.

Arthroscopic Knot Diagrams

These diagrams show knot configurations without half-hitches; locking half-hitches must be added for adequate knot security clinically.

FIGURE 5-8 Tennessee slider; sliding knot configuration. Locking half-hitches must be added.

FIGURE 5-9 Duncan loop; sliding knot configuration. Locking half-hitches must be added.

FIGURE 5-10 SMC knot; sliding-locking knot configuration. Locking half-hitches must be added.

FIGURE 5-11 SD knot; sliding-locking knot configuration. Locking half-hitches must be added.

FIGURE 5-12 Weston knot; sliding-locking knot configuration. Locking half-hitches must be added.

FIGURE 5-13 Revo knot; nonsliding knot configuration.