Name: Knot Tying Studies
Uploaded: 2013-02-28T00:00:00Z
Channel: Arthrex
Description: In this study presented by Dr. Bryan Hanypsiak under the guidance of Dr. Stephen Burkhart, the knots of more than 70 accomplished shoulder surgeons are tested against Arthrex knotless suture constructs. Knotless sutures consistently provided a more dependable strength, while the knots tied by surgeons seemed to produce less consistent load to failure.

<p>In this study presented by Dr. Bryan Hanypsiak under the guidance of Dr. Stephen Burkhart, the knots of more than 70 accomplished shoulder surgeons are tested against Arthrex knotless suture constructs. Knotless sutures consistently provided a more dependable strength, while the knots tied by surgeons seemed to produce less consistent load to failure.</p>

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VPT1-0001-EN | A | Knot Tying Studies

Bryan Hanypsiak

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Knot Tying Studies

We're going to talk about our knot tying studies. We recently did two studies which I think will help you overcome some of the anchor debate that's out there. I think this is particularly applicable to the juggernaut and the single row versus double row arguments. So I'm just going to take a little bit of time and and go through what we found in our research. So the first one is entitled knot strength varies widely among expert arthroscopies. It's been submitted for publication and includes Steven Burkhart and Walt Lowe as authors on it. Our hypothesis was the first that skilled arthroscopic surgeons would be able to tie arthroscopic knots of similar strength. We also thought that surgeons who are less than ten years in practice, would achieve more consistent results because they were trained during their residency and fellowship programs in arthroscopic surgery. So the guys who are just coming out have had the advantage of being able to practice and learn from their mentors, whereas the guys who've been out more than ten years had to learn during their practice. And I think that's often less successful. And we felt that surgeons who performed more than 200 arthroscopic shoulder cases per year would outperform those who perform fewer arthroscopic cases. So those are the things we're going to look at. So for our methods, we took 73 independent expert orthopedic orthopedic arthroscopies. These were all of our master shoulder instructors. And we had each surgeon tie five of their favorite knot. The one they use in the operating room, the one they're most comfortable and familiar with. We didn't want to test knots, different types of knots against different types of knots, because Steve Burkhart has already published a landmark paper in arthroscopy, which has already done that. So what we wanted to look at is the ability to make all the knots, whichever one you use, the same strength. So we tied five consecutive knots. We photographed, labeled them and numbered them one through five, and then tested each mechanically on an instrument for maximum load to failure and clinical failure for clinical failure. We identified that as being three millimeters of construct slippage. And I think it would be fair to say that if you did a bankart reconstruction and it was loose by three millimeters, that that would be a failure and you wouldn't expect it to work. So that was an arbitrary number which we picked. And I want to show you what we got. These are some of the knots that were tied. And we took a picture of every night. And you can see that there's a tremendous variation in the appearance of the knots. And then when we look at the sets of five it's almost like a which one doesn't belong. But if you look some of the knots that these were all tied by the same surgeon in the same setting back to back, and I would challenge you to tell me that any of these look alike. So there's a there's a tremendous variation in even the appearance of the knots. So what happened when we put them on the instron? Well, the first thing we did was look at maximum load to failure, which was to put the knots on the instron and pull them. And as the construct slipped three millimeters, we generated the clinical failure number. And then as it finally broke and gave in, we got the maximum load. So when we looked at first group surgeons who were less than ten years in practice, we found that those surgeons tied statistically significant, better knots than those who were more than ten years in practice. But when we looked at maximum load for those doing more or less than 200 cuff repairs per year, we found that it didn't matter. So it didn't matter how many surgeries you did. If you tied a knot, you tied a good knot. If you didn't, you didn't. You just tied that bad knot more times that year. So then when we looked at clinical failure, which was three millimeter of slippage. We looked at more or less than ten years in practice. And we found that there was no statistical difference in whether or not your construct failed clinically. And that was true also for more or less than 200 rotator cuffs. Now the interesting thing comes in when you look at variation. So we looked at the distribution of maximum load and we looked first at individual surgeons. So out of the 73 surgeons that participated in the study, only 27 of them or 37%, were able to tie the knots within 20% of the mean. So basically, it's a huge bell shaped curve, and there was tremendous variation in large standard deviation. We noticed that there was no significant difference from not one to not five. So doctors weren't getting tired as they tied the five knots. They were all the same. Then when we looked at the individual knots, the 365, only 18% were within 20% of the mean. So again, a tremendous variation in the strength of the knots. When we looked at clinical failure, we found the identical picture. Most of the knots fell outside of the average knot strength in the study. Then when we looked at knot stack height, we found something very interesting. Out of the 365 knots, the average knot stack height was 5.6mm. That's over half a centimeter. I don't know how much room there is between the rotator cuff and the acromion on an average patient, but I don't think it's more than a centimeter, and it certainly might be half a centimeter. So these knots take up a significant amount of room in the subacromial space. And I would challenge anyone to say that you're not celebrating the undersurface of the acromion is a problem. Isn't the problem. Excuse me. Okay, so then we looked at the Enstrom charts for consistency, and we found that some surgeons were able to consistently tie great knots straight across the spectrum. So the top two are good examples of consistently well tied knots. The bottom chart is one of our surgeons who was great at tying bad knots. These had the lowest standard deviation of anyone, and they were all equally bad. So there's consistent charts in both spectrums. Looking at inconsistency. When you look at the standard deviation, the numbers are very high here. And you can see that these charts are all over the map. One knot to the next is completely different. And then we found something really interesting. There were some that if you just looked at the numbers, they looked consistent and And consistently good. There were others that when you looked at the charts, you said, wow, these numbers don't match up with what we're seeing. So let me show you the one on the bottom first. This was the guy who tied what we thought were the best knots. We wanted to study what he was doing that made his not so good look at the max load 339 Newtons with a standard deviation of six. These are all consistently strong, but we went back and looked at this window here, which was the clinical failure. He tied some of the worst knots. So it was 88 newtons of total strength with a large standard deviation. So what we found was that he wasn't actually a good not tire. He was good at tying knots that functioned like Chinese finger traps. The harder that instrument pulled, the tighter those knots got, the higher the maximum load. But in reality, his knots were going to fail clinically much faster than anyone else's. Again, here you look here. This is tight standard deviation in clinical failure and max load. There's a wide deviation. Again here you see the same construct. So even within the not pictures themselves the numbers don't always tell the whole story. So then we looked at anchor pullout. And I wanted to look and see how those knots did against the anchors. Because everyone knows the anchors generally don't pull out anymore. When something fails, particularly in the cuff, they cut through the tissue. Right? Well, what I wanted to do is see what happened when you added the clinical variance in knot strength to this. And what we found for SwiveLock Corkscrew all of the most popular anchors out there that on average, only 66% of the knots tied exceeded the pull out strength of the anchor, which meant that one third of the anchors placed were at risk for clinical failure just from pulling on the anchor. Now, we don't know the force that they see exactly, so it's only Conjecture, but I would tell you that it's quite possible that if you do a three anchor bankart repair, you've done a two anchor Bankart repair, unless you've done knotless fixation, because there's concern about that not failing. So in conclusion, there's considerable variation in knot strength between arthroscopic knots of the same type tied by the same surgeon. This variation has the potential to affect the integrity of arthroscopic repairs, and I would suggest that independent, objective testing of knots should be part of a surgeon's training. I learned how to tie knots as a resident and again as a fellow, but no one ever checked to see if I was actually good at it or tied good knots. So my suggestion is maybe our clinical programs and our fellowships should test their residents, test their fellows to make sure they're doing the right thing. So that was the study one we wanted. And we suspected that using Knotless fixation would be more consistent than tying anchors, but we couldn't really say that because we didn't test Knotless fixation. So the next logical step would be to put Knotless fixation head to head against tied suture anchors. And our hypotheses were that the pull out strengths of knotless anchors would be more consistent than knotted anchors. The time to complete a knotless construct would be significantly shorter than for knotless anchors, and that knotless anchors would have less slippage of the construct prior to failure than knotted anchors. So we repeated our methods. What we did is we took 71 independent expert orthopedic arthroscopies, and we had them tie three anchors in foam block, tying their knots or placing their knotless fixation over the steel bar, which coincidentally matched the instron. And what we did then is we had them tie the three knots and we timed them on every knot, and we had them place the swivel locks and we time them on each knot. We also measured the knot stack, and then we tested for clinical failure and maximum load to failure, just like we did in the previous study. This is what the station looked like. Again, we went in order and photographed all of them until they were complete. We did those for both the tied anchors and for SwiveLock. In looking at the results, when we looked at clinical failure, which was three millimeters, knotless fixation and knotted anchors were equivalent. That is the only condition which is still arguable of what the what that means three millimeters of failure where these were equivalent in all other aspects. Knotless fixation was superior to tied. Suture anchors. When we looked at maximum load to failure and we looked at standard deviation, the p or theoretically f values. Looking at. Variation between the standard deviations were statistically significant. Even though the tide suture anchors were slightly stronger, the variation. Was much greater, so these were more likely to fail because of a poorly tied. Not if you could tie consistently five knots. These anchors were slightly stronger. But we know from our previous study that you can't. Looking at extension and slippage. The tied suture anchors for maximum load stretched twice as far as the knotless. Construct before maximum load was achieved, and that was statistically significant. When we looked at time, it took 82 seconds to put in a tied anchor and 40s to. Put in a SwiveLock twice as long, and that was statistically significant. Look at those. P values, not stack height 5.35. Nearly identical to the number we got on our other study. Swivelock essentially zero. There was no not stack. So in conclusion, our SwiveLock and tied anchor performance was equivalent at conditions set for clinical failure. At all other conditions, the SwiveLock was superior. The SwiveLock was five times more consistent than a tied anchor at maximum load to failure. The SwiveLock was two times faster than a tied anchor to be placed, so it improves your operating time. And the SwiveLock had a nod stack that was zero and half a centimeter smaller than any tied anchor. So I would take that information out, get it out there, because not less fixation is faster. It's more consistent. It is just as strong. And it doesn't leave a not stack behind to cause problems later inside the patient's shoulder intra-articular or in the subacromial space.

Knot Tying Studies

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