Arthroscopic Knot Tying

Robert K. Lieurance, M.D.
Wesley M. Nottage, M.D.

I. Introduction:

The ability to re-approximate tissues arthroscopically utilizing suturing techniques is an essential skill for the reconstructive surgeon. Whereas knot tying in open surgery is easily learned and performed by surgeons, knot tying becomes both challenging and frustrating when performed arthroscopically. While there have been a multitude of studies evaluating various suture characteristics and knot performance, there has been no presentation discussing the basics of arthroscopic knot tying and the technical considerations when performing arthroscopic repairs.

Proper knot tying in arthroscopy should proceed from practicing in a “dry-lab” setting using large suture or cord and then progressing to tying with standard suture material. Tying and passing knots through cannulas again in a “dry-lab” setting should follow this. After the surgeon is comfortable with the technical aspects of tying and tensioning knots, a cadaver specimen should be utilized to become comfortable with correct placement of the cannulas, the steps required to place sutures through tissue, the placement of anchors, and the steps required to prevent suture twisting, soft tissue entrapment , or loss of knot tension. The time spent practicing proper knot tying prior to surgery will greatly increase the speed with which the procedure is performed and will greatly reduce your level of frustration.

Terminology:

When sutures are to be tied the ends of the suture are called “limbs”. The “limb” of the suture that the knot will be tied around is called the “post”. This is typically the limb which is away from the bone and through the soft tissue or the limb on which you want to slide the knot down to re-approximate the tissues. The other strand is called the “loop”, and is the limb which is tied into a knot around the post strand or looped around the post strand. The knots are created and pushed down the “post” by the knot pusher which advances the knot, or alternatively, the knot “pusher” is placed on the loop strand ahead of the knot and the knot is “pulled” down the cannula into the joint.

II. Knot Delivery:

Instrumentation:

Suture Material:

As with open surgery, a variety of suture materials are available for use in arthroscopic surgery. The choice of suture material is based upon the inherent suture characteristics and surgeon preference. The sutures may be absorbable or non-absorbable, monofilament or braided

Non-absorbable suture (such as Ethibond - Braided polyester) typically requires extra steps for placement and may become frayed with handling, but provides permanent fixation and the knots tend to lay down better. It also has increased pliability and ductility, and overall increased strength. In addition the roughened surface adds to knot security.

Absorbable suture (such as PDS - monofilament polydiaxone) can usually be placed easier and provides a slippery surface for sliding knots which are easier and quicker to tie. However, it is stiffer to work with, and more difficult to get knots “tight”, is weaker and tends to stretch with repeated cyclic loads.

Cannula:

In order to prevent the entanglement of soft tissues, arthroscopic knots must be tied outside the joint and passed down a cannula. Clear cannulas are very beneficial as they allow visualization of the sutures and knots as they pass down the cannula. The clear cannulas also allow the cannula to be advanced down near or onto the knot, allowing the knot to be tied almost entirely within the cannula. Also, threaded cannulas are useful to help prevent the cannula from backing up out of position.

Knot Pushers:

Knot pushers come in a variety of fashions from single-holed knot pushers to double-holed, slotted, a mechanical spreader, or the 6^th Finger Knot Pusher (Arthrex) to name a few. There are advantages to each and it should be based on surgeon preference and comfort with an individual knot pusher.

III.Type of knots:

The various knots include square knots, sliding knots, the Revo knot, and multiple half hitches. While there are dozens of different knot configurations and modifications, in reality an arthroscopic surgeon need only be familiar with two knots: a sliding knot and a non-sliding knot, and he will be able to handle any given knot tying situation.

Knots:

      Non-sliding knots:

              Square knot

              Revo knot

              Half hitches

      Sliding knots:

              Duncan or Hangman’s knot

              Roeder knot

              Lieurance Modified Roeder knot

              Tennessee Slider

Technique:

Prior to any discussion of actual knot tying, there are several steps that need to be understood and followed every time a suture is placed and prepared to be tied.

1.   One pair of sutures at a time should be isolated through a cannula for tying. Additional sutures should be withdrawn through an accessory cannula or placed outside the working portal.

2.   It should be determined if the suture slides freely or if a non-sliding knot will need to be tied.

3.   It is helpful to have the assistant stabilize the cannula in line with the sutures so that no suture fraying occurs on the edge of the cannula.

4.   The suture should be checked to make sure there are no twists of the suture limbs within the cannula, and that there is no soft tissue entangled around the sutures. Soft tissue entrapment happens quite frequently as instruments are passed down the cannula. When the diaphragm is disrupted, water squirts out the cannula “vacuuming” tissue up with it. If the twists in the suture or soft tissue are not removed the knots will “lock” within the cannula preventing proper seating of the knots. Frequently, when attempts are made to forcibly “push” the locked knot down, the suture will break. (It is very helpful to use the “double-holed” knot pushers to check for suture twists. Each limb is placed through one of the holes of the pusher and the pusher is advanced down the cannula. The twists are easily visualized and removed by un-twisting the knot pusher thus removing the twists).

5.   Next, the pusher is withdrawn and with the assistant stabilizing the cannula, the assistant places a finger between the parallel suture limbs as the knot pusher exits the cannula. This keeps the suture limbs from re-twisting. The “double-holed pusher” is then removed.

6.   The post strand is then identified and a “single-hole” knot pusher is placed on the post strand and a hemostat is clipped onto the end of the limb to “identify” it as the “post”. (Technique varies dependent on the type of knot pusher used). The knot pusher is again passed down the cannula to check and make sure the pusher is on the “post” and to double-check for any soft tissue or twists in the suture.

7.   The tissues to be tied should be relaxed. Tension on the tissues can be decreased by internally or externally rotating, or abducting or adducting the shoulder to relax the tissues or a traction stitch can be placed.

8.   The knot of choice is then tied and advanced into the joint. Each time the “post strand” is changed, the knot pusher should be placed on the post and again the hemostat is placed to identify the “new” post.

9.   Every time the “post” is switched, the knot pusher should be run down the “new” post to check for twists or soft tissue. (This is an important step and can prevent complications with seating the half-hitch throws).

10. After the knot is tied, it should be cut approximately 3mm from the knot using either an arthroscopic basket or scissors, or one of the commercially available suture cutters.

If these ten steps are followed every time a suture is to be tied, it will greatly reduce the difficulties and frustration associated with arthroscopic knot tying.

Non-sliding knots :

Square knot:

Square knots are difficult to tie arthroscopically. If tension is applied asymmetrically to the limbs the knot converts to two non-identical half hitches, and once the knot seats it is very difficult to tension. However, this is being made somewhat easier with the use of the mechanical spreader types of knot pusher/tiers. Nevertheless, it still remains difficult to maintain tension in the knot between successive throws.

Technique:

Place an overhand loop around the post strand and place a single hole knot pusher on the loop limb and pull the loop limb into the joint by passing the knot pusher beyond the loop, holding it in that location and applying tension on the free end of the loop strand to pull the first loop into position. Snug it down by keeping the knot pusher beyond the knot on one side and apply tension on the post limb. Inspect the knot to confirm that it is not a half hitch, and if desired the knot may be clamped from an alternative portal to maintain tension.

Back the knot pusher up the loop suture and pass an underhand loop around the same post and advance it into the joint as above using the knot pusher still on the loop suture. Seat the knot by moving the knot pusher to the post suture and passing it beyond the knot again applying tension to tighten and secure. Additional loops can be applied if needed.

Revo knot:

The Revo knot is a knot consisting of multiple half hitches made by alternating the post and direction of half hitches.

Technique:

To tie this knot, an underhand knot is thrown around the post and with the knot pusher on the post strand, the half-hitch is pushed down the post with alternating tension on each strand until the half-hitch is tightened on the tissue. Back off the knot pusher while still holding tension on the post strand and throw another underhand half-hitch and similarly push it into the joint until the knot is seated. Again, maintaining tension on the post strand, an overhand half hitch is thrown around the post and “walked” down into place. This knot is then further tensioned by “past-pointing”, (relax the loop strand and push the knot pusher past the knot on the loop strand and then apply tension to both strands while holding the pusher past the knot. This further tensions the knot). The knot pusher is then switched to the other suture limb, i.e. the “new” post and an underhand half hitch is placed and tensioned. The post is again changed and an overhand half hitch is placed and walked down the post and tensioned again by “past-pointing”. The tails of the suture are then cut 3-4mm from the knot.

Alternatively, the half hitches may be “pulled” into the joint by placing the knot pusher on the loop strand “ahead” of the loop to drag it down the post. This allows you to tighten the knot in the joint by “past-pointing”. The above steps are repeated, but by “pulling” instead of pushing. ( This is somewhat easier and smoother than “pushing” the knots down and can help “protect” the suture from breakage if it has become frayed).

Sliding Knots:

A variety of sliding knots have been devised to allow the surgeon to tie tissue under tension. Sliding knots require the suture to slide freely through both the tissue and the anchor and are reinforced by a series of additional half hitches to prevent slippage.

Technique:

In order to tie a sliding knot, the post strand must be made as short as possible and the loop strand is made as long as possible. (The “post” strand is made short and the “loop” strand is made long so that as the knot is pushed into the joint, you end up with two fairly even suture limbs with which to tie the remaining half-hitches and not a very short loop limb!) The knot pusher and hemostat will be placed on the post strand. The sliding knot is then tied around the post strand, tightened, and pushed down into the joint.

 

Duncan, Hangman’s, or Fisherman’s Knot:

Technique:

To tie the Duncan Loop, verify that there are no twists or soft tissue entanglements and that the suture slides freely. Begin with two uneven, parallel sutures and grasp them between the thumb and index finger. Throw three to four successive loops around the post with the first around your thumb, or alternatively, make a loop in the loop strand and pinch this between your thumb and index finger followed by the successive 3-4 loops around both the post and loop strand. Then pass the tail of the loop strand up through the loop of suture around your thumb (or pinched between your thumb and index finger) and pull on the two sides of the loop strand to tighten the knot and snug it down tightly. This is then pushed into the joint with the knot pusher while pulling on the post strand. Tension is then maintained on the post and the first half hitch is placed on the same post strand. The post is then changed and an opposite throw is placed and tensioned. The post and direction of throws is alternated to give a total of three to four half hitches to prevent slippage of the sliding knot.

Roeder Knot:

Technique:

As with the Duncan loop, begin with two uneven, parallel limbs. Throw the first loop around the post strand only, the second loop around both limbs, and the third loop only around the post strand, passing the tail of the loop limb between the two parallel strands, between the second and third loops. The knot is again seated and tensioned and pushed into the joint. This is again secured with a series of half hitches alternating direction of throws and utilizing post switching.

Modified Roeder Knot:

Technique:

The Roeder knot has been modified in several ways. One way is to add an extra loop around both sutures and again passing the tail between the parallel strands, between the third and fourth strands.

The Lieurance modification is to tie the standard Roeder knot, but after passing the tail between the second and third loops, the tail is then brought back up and through the initial loop and pulled into the joint without pre-tensioning the knot. This provides a “self-locking” knot which is secured with alternating half hitches.

Lieurance-Modified Roeder Knot:

Technique:

Begin with two uneven, parallel limbs. The short is the “post” and the longer limb is the “loop strand”. Throw the first loop around the post strand only, the second loop around both limbs, and the third loop only around the post strand, passing the tail of the loop limb between the two parallel strands, between the second and third loops. The tail is then brought back up and down through the initial loop. This is then “loosely” tightened, making sure not to pull on the “loop strand” as this will “lock” the knot. This is then pulled into the joint without pre-tensioning the knot. The knot pusher is pushed down on the “post” strand. The “post” strand is then pulled on while pushing down on the knot. With the knot pusher firmly against the knot, the “loop” strand is then pulled, locking the knot. This provides a “self-locking” knot, which does not “back-up” when tension is relaxed on the post. This is then secured with alternating half hitches.

Tennessee Slider:

Technique:

The Tennessee slider is essentially another modification of the Roeder knot. To tie the Tennessee slider, the sutures are again made uneven and parallel. The loop strand is thrown around both the post and loop strand one time and then around the post strand only and is brought up between the parallel limbs between the first and second loops. This is tensioned and pushed into the joint and again backed up by a series of four alternating half hitches with post switching.

 

IV. Biomechanical studies:

There have been multiple studies evaluating knot performance, suture strength, and ways to optimize arthroscopic knots. Arthroscopic surgeons should be aware of the best methods for optimizing their knots.

In 1995 Loutzenheiser et al. showed that the most secure knot configurations were achieved by alternating the direction of throws of the half-hitches and by alternating posts when utilizing monofilament suture. In 1998, Loutzenheiser et al. performed a similar study utilizing braided suture.

A recent study by Mishra et al. in 1997 showed that the most important factor in knot security was the type of suture material used. They noted a high percentage of knots tied with monofilament suture failed by knot slippage despite utilizing nonidentical half hitches and post-switching. They noted that knots tied with non-absorbable braided suture tended to fail by suture breakage., similar to square knots

 

V. Summary:

Arthroscopic suturing and knot tying may be applied to repairs of the rotator cuff, Bankart lesions, capsular shifts, and meniscal repairs. The ability to tie secure arthroscopic knots is of paramount importance to the successful completion of these repairs. It is important that surgeons performing arthroscopic repairs be aware of the differences in knot strength and security afforded by different suture materials and knot patterns. A surgeon only needs to know one sliding knot and one non-sliding knot to be able to handle any given clinical situation. Extensive time should be spent practicing these knots and practicing placement of the operating cannulas in order to minimize the difficulty associated with these procedures.

 

VI. Bibliography:

1.      Loutzenheiser TD, Harryman DT II, Yung SW, et al: Optimizing arthroscopic knots. Arthroscopy 11: 199-206, 1995.

2.      Trimbos JB, Van Rijssel EJC, Klopper PJ: Performance of sliding knots in monofilament and multifilament suture material. Obstet Gynecol 68: 425-430, 1986

3.      Mishra DK, Cannon WD Jr., Lucas DJ, Belzer JP: Elongation of arthroscopically tied knots. Am J Sports Med 25: no 1. 113-117, 1997.

4.      Van Rijssel EJ, Trimbos JB, Booster MH: Mechanical performance of square knots and sliding knots in surgery: A Comparative Study. Am J Obstet Gynecol 162: 93-97, 1990.

5.      Sharp HT, Dorsey JH, Chovan FD, Holtz PM: The effect of knot geometry on the strength of laparascopic slip knots. Obstet Gynecol 1995;86:536-40.

6.      Tera H, Aberg C. Strength of knots in surgery in relation to knot, type of suture material and dimension of thread. Acta Chir Scand 19977;143: 75-83.

7.      Tera H, Aberg C. Tensile strengths of twelve types of knot employed in surgery, using different suture materials. Acta Chir Scand 1976; 142: 1-7.

8.      James JD, Wu MW, Batra EK, Rodeheaver GT, Edlich RF: Technical considerations in manual and instrument tying techniques. J Emerg Med 1992;10: 469-480.

9.      Zimmer CA, Thacker JG, Powell DM et al. Influence of knot configuration and tying technique on the mechanical performance of sutures. J Emerg Med 1991; 9:107-113.

10. Herrmann JB. Tensile strength and knot security of surgical suture materials. Am Surg 7, 209-217.

11. Barber FA, Click JN. The effect of inflammatory synovial fluid on the breaking strength of new “long lasting” absorbable sutures. Arthroscopy. 8(4): 437-4411992.

12. Loutzenheiser TD, Harryman DT II, Ziegler DW, Yung SW. Optimizing arthroscopic knots using braided or monofilament suture. Arthroscopy. 14(1), 1998, 57-65