Hi, I'm Mark Safran from Stanford University. I want to thank John Christopheretti and Al Stubbs for inviting me to speak about recognizing and treating hip micro-instability. This is an area of my particular interest. I'm going to try to go over as much as I can in 15 minutes, but that's a lot to cover. So what I would recommend for some background information if you want is to go to the Journal of the AAOS where I published a paper on the micro-instability of the hip and talk a lot about the basic science, the clinical science that we know to this point. And that covers about 80% to 90% of what I'm going to talk about here today. And that was published in January of 2019. So to treat micro-instability, you got to be able to make the diagnosis. And so that's the key. And what we say is that the eyes don't see what the mind doesn't know. So hopefully you know some of this stuff and maybe this will open your eyes a little bit more. But we'll review the latest clinical and imaging clues to make the diagnosis. We'll talk about the arthroscopic findings that I think will help confirm the diagnosis. Then we'll talk a bit about management. I'm not going to go into a lot of detail, but we'll just kind of give an overview to the management as somebody else is giving that talk. But do realize I'm not talking about hip dislocations, but hip micro-instability. Hip dislocations tend to be more posterior clinically. The hip micro-instability tends to be more of an anterior phenomenon, and we'll go over the pathophysiology of that. So the key is that with an individual that has hip micro-instability, they rarely complain of injury. Some might have a minor injury, but more often than not, it's an insidious onset. They may have a diagnosis with Ehlers-Danlos syndrome or benign hypermobility syndrome, or they might know that they've had a history of hip dysplasia. One of the things that you rarely get in the history of these individuals is that they rarely complain of instability. People that complain of instability, we were always taught, were those individuals that had external snapping hip. But people with true micro-instability rarely complain of instability. The first thing is to look at how the patients are when they're lying down. When they're laying supine, you can check their internal external rotation, but when they're just laying, here you see this individual that has right hip pain. His foot is externally rotated about 30 degrees or so on the normal side, but on a symptomatic side, it's more like 60 or 70 degrees of external rotation. That's consistent with iliofemoral ligament laxity. You can do the so-called dial test as described by Mark Philippon, where you internally rotate and then let the foot rotate out. And then you can see where it sits as it rotates out. You can see the recoil as well as how much external rotation there is. Again, giving a clue to instability if there's differences side to side. One of the nice tests I like is the abduction external rotation extension test. So you abduct about 45 degrees, you extend, you externally rotate, and you apply an anteriorly directed force on the greater trochanter. When we studied this, we found this to be the most accurate test for patients with hip micro-instability with an 81% sensitivity and an 89% specificity for the diagnosis of hip micro-instability. Another test described by Ben Dome, if the patient is prone, you externally rotate, put an anteriorly directed force on the posterior greater trochanter. If that causes pain anteriorly, again, that's a clue to potential micro-instability. We found this to be the most specific test with only a 33% sensitivity, but a 98% specificity for the diagnosis of hip micro-instability. A third test that we like to use is a classic hyperextension external rotation test for the patients at the very end of the table, the hip is hyperextended and you externally rotate it. And we found that this has a 71% specificity and 89% sensitivity. So again, a very important test. Can I actually do that one over? I'm gonna go back because I clicked too early. So- No problem. Okay. So I'm gonna start over here. Okay. The next test we'd like to test is the hyperextension external rotation test for the patients at the end of the examining table. They're hyperextended and then you externally rotate their lower extremity. We find that this has the second best sensitivity at 71% and a second best specificity at 85%. Again, the key is that the good leg is actually flexed to help lock the pelvis in place when you do it. If you have two of these three tests positive, the patient has greater than a 90% likelihood of having a diagnosis intraoperatively of hip micro-instability. Looking at radiographs, you can get a lot of clues from plain x-rays about patients with potential for instability. Certainly we know for hip dysplasia, a center of jangle of less than 25 is consistent with dysplasia on an AP pelvis. You also don't wanna get a false profile or Lecunier view to see about the anterior center of jangle, which also should be greater than 25. If not, you need to think about dysplasia there. A high tonus angle is another clue with an acetabular index of greater than 10, which is a high tonus angle that would be consistent with dysplasia as well. Other clues that you can get that are not necessarily objective in measure, you can look for excessive femoral on an acetabular interversion, but here you can see a high anterior wall. You see that it's quite high, not really covering the femoral head on a well-positioned AP pelvis x-ray. You wanna look for coxa valga, narrow iliac wing will also give you a clue to the pelvic rotation and sweat obturator foramen. We described the so-called cliff sign. This is where the femoral head kind of just drops off from being a sphere. This is a non-operative patient, and you can see how that, as you try to fit a ball over the femoral head, that it just kind of drops off like a cliff. So you can see this on an AP pelvis x-ray. This is another cliff sign patient, but you can also see it on a patient on a lateral view. And so I don't see them generally both on the AP and lateral, so it's one or the other, but you definitely can see this on AP views as well as lateral views, and it should be a clue for instability of the hip. Josh Harris described the so-called splits radiograph, where he has the patient sitting upright, doing the splits, and their legs are in external rotation. And they looked at 47 professional ballet dancers, and they found that almost 90% had femoral head subluxation on the splits radiograph, and another 36% had what they call a vacuum sign. So you can see that looks like there's almost air in the joint itself, so the so-called vacuum sign. They found that femoral head subluxated on average 1.4 millimeters in these asymptomatic ballet dancers. John Sakki and the group at the University of Michigan looked at both the anterior hip joint recess just lateral to the zone of the obliquus on an axillary oblique view, and they also described the thickness of the capsule over that same area. And they found that that was consistent with micro instability of the hip. We looked at this as well in our patients and found that with those individuals that had a capsule of thickness of less, a few millimeters or less, especially in women tended to have a micro instability of the hip as well. Other clues on an MRI, you can look for a capsular defect as you see here, or a ligamentum teres tearing. Martin Beck described a so-called fear index. He was looking at patients with borderline dysplasia and wanted to know if whether or not their problems were related to instability or related to impingement. So he measured an angle between the line from the acetabular inclination or the roof angle and that of the fissile scar. And so here you can see, you take your acetabular inclination and you take your fissile scar and you project them out and you can make an angle. And what he found is that those patients with borderline dysplasia that had a fear index of less than five degrees had a 79% probability of correctly being assigned as being stable. We looked at the same thing in patients that had borderline dysplasia, but also that did not have borderline dysplasia but were unstable and compared them to a group of patients with FAI. And what we found is that the fear index also holds true in a group of patients that don't have borderline dysplasia but do have instability. So once you've made the diagnosis of micro instability, how do we treat it? Well, generally you start off with a non-operative treatment. And we look at this similar as we do to the shoulder. So patients with shoulder micro instability, we do periarticular muscle strengthening and we do this for the hip itself as well as core. So working on the iliopsoas, working on the glutes as well as your short external rotators and core strengthening. We also have them do activity modification during the rehab period. And so we looked at a group of 64 patients with micro instability, 63 of them were women, which is more like my practice, greater than 95% of my patients with instability are women. The average age was 32. And we sent them for formal physical therapy and a home exercise program for about at least six weeks where they worked on hip and core strengthening. And with a mean follow-up of greater than two years, actually almost four years on average, 51% of the patients had improved. 30% overall ended up coming to surgery. When we looked at our athletes, half ended up coming to surgery, but the non-athletes less than a third needed surgery. So if they fail non-operative treatment, then what do you do? Well, if they have bony deficiency, in other words, if they have dysplasia that's not borderline or is more significant, then we'll send them for a periacetabular osteotomy. If the problem is related to excessive femoral antiversion, we'll send them for a derotational femoral osteotomy. If the problem is capsular laxity, so it's not really a significant bony cause to it, somebody who has ligamous laxity like Ehlers-Danlos or benign hypermobility syndrome, or if they just have repetitive microtrauma, like you see your dancers that are doing, trying to turn out all the time and stretch the iliofemoral ligament, or possibly residuals from a prior hip dislocation, or even those with borderline dysplasia. So they have some laxity and some mild bony deficiency. I think all of these can be addressed through the capsule. Ways we can confirm this intraoperatively is looking at how easy it is to distract the hip. And so on our table here, it takes only 11 turns. If it takes 11 or less turns to get more than eight millimeters of displacement of the femoral head from the acetabulum, that's consistent with micro instability. Here, this is a picture of a fluoroscopy from a patient that we just pulled on their leg to get rid of the slack between the perineum and the post. And you can see the femoral head already is distracted. And then once we have some distraction, we put in the needle to remove the negative pressure. And that's your air orthogram. Now the pathophysiology of micro instability is you get this femoral head motion relative to the acetabulum. It tends to be anterior and you get this labral chondral separation and you get this inside out wearing pattern as opposed to an outside in pattern that you'd see with FAI. So what you find at the time of surgery on the acetabular side, you'll see labral tear at the labral chondral junction, straight anteriorly. You'll also see an associated inside out wearing pattern of the articular cartilage, usually from one to three millimeters and from the acetabular rim. But you can also see it straight laterally if you see this patient and intact. This is looking from a post-lateral portal and intact labrum. And you can see the articular cartilage is worn at the periphery at 12 o'clock. On the femoral side, you'll find chondral damage around the central portion of the femoral head. And oftentimes ligament of teres tears will also be seen. So once you've made the diagnosis, how do you treat it? You can do this as an open capsuloraphy or you can do an arthroscopic, thermal or suture capsulorplication. So this is a video of one of my patients from almost 20 years ago now, where I did a thermal capsuloraphy and what we did was we used a striping technique. And this patient was still doing well at 16 years follow-up. We've abandoned this because of the concerns or the risk of what if happened in the shoulder with a capsular necrosis, which we did not really see in the hip. And that might be because we're doing a striping technique. It might be because the capsule is thicker or it might be that you're getting more support from the bony acetabulum than you do from the glenoid. But we did find this very useful, but we did go away because we were worried about the risks to the capsule from the thermal denature of the collagen. So Mark Philippon did publish on thermal capsuloraphy in 2001. Ben Dome developed technique of inferior capsular shift, where he takes his interportal capsulotomy and actually shifts the capsule up to tighten up the iliofemoral ligament and a bunch of patients that had borderline dysplasia, about half of which ended up also having cam resections. And then Chris Larson published on a group of Ehlers-Danlos patients where he did FAI surgery on 96% of the patients, but also then tightened up the capsule and found good exome results in greater than 80%. And all three series. So that does suggest that capsular tightening is beneficial. We took several years to get our paper published on doing isolated capsuloraphy, as microinstability was more of a controversial topic 10 years ago. But I had 32 patients, all female, that had capsulifications without any bony surgery. So we were just doing labral surgery and tightening the capsule. 29% had center age angle of less than 25 and almost half had a tonus angle of greater than 10. So somewhere between a third and a half had evidence of bony dysplasia or borderline dysplasia. All the patients had improved. There were no reoperations, no increased symptoms, and no loss of motion in this group. And a third of the group that were college athletes or professional athletes all returned to their sport. Not even included the patients with the dysplasia. So the way we do this is if, in blue is the iliofemoral ligament and green is the ischiofemoral ligament. So this is looking from the side. I take out a piece of the capsule in the non-ligamentous portion of the capsule itself. We place some sutures in it and that causes a plication that helps tighten up the ischio and iliofemoral ligaments just like a rotator interval closure would in the shoulder. Now, for those cases of iatrogenic instability, those that are doing capsulotomies that are interportal capsulotomy that cuts the iliofemoral ligament or T-capsulotomy that also cuts the zona obicularis, you can have some residual micro instability. And this does not always heal. And so here you can see a patient that I had to do a revision on. Here's the labrum, the femoral head, the capsule, and you can see the iliopsoas tendon, which you should not normally be able to see. You see it because there's a capsular defect. And so in this situation, again, you can oftentimes see this on MRI as well. You can go ahead and try to close this. Frank McCormick published Shane Nose studies where he looked at patients that had failed arthroscopic surgery. This was after they did an interportal or T-capsulotomy without closing it. And on MRI, 78% had capsular defects and iliofemoral ligament defects. When he closed it, that number dropped significantly, but still there are patients that end up with capsular defects. And so the goal is to try to repair the capsule. The reality is that the capsule does not attach to the labrum. It's more in the acetabular region above the labrum. So knowing that here, you can see I placed the anchors above the labrum itself, labrum itself, and then just tightening down the capsule to do a repair, primary repair of the capsule. Steve Aoki looked at 1,100 patients of his. 33 developed instability, including two frank dislocations. And this was again, when he was doing interportal capsulotomy without closures. He did a revision arthroscopy with capsular closure for these patients and all improved with revision, regardless if he did additional procedures or not. And lastly, if you have a capsular defect that's irreparable, what do you do? Some people will do capsular reconstructions. This was a paper that was published looking at IT band allograft that showed that improved structure and stability, but it also, people have to use autograft to try to repair the defect itself and has shown to be beneficial. But I think there's still more to learn about capsular reconstruction. For an example, this is a professional tennis player that was referred to me after having a revision of arthroscopy with a dermal allograft capsular reconstruction. And here you can see that femoral head. And here you see the native capsule. And there you see the allograft capsule that did not heal along its lateral suture line that we had to re-repair. So in summary, hip microincisibility is real. There's an increasing ability to make the diagnosis preoperatively based on examination, as well as plain radiographs and even some clues on MRI. Patients with dysplasia and Ehlers-Danlos syndrome are not the only patients that have microincisibility. You can have it in individuals that don't have either of these diagnoses. So the key is to treat the underlying cause. Start with rehabilitation, as that can be very successful in a large number of your patients. All the capsular placation studies report excellent results of greater than 80%. But we still need more data to objectively measure how lax they are, as well as how much we're tightening them in the operating room, and what is the best technique to placate them. Again, I thank John and Al for inviting me to come speak and enjoy the course.

hip micro-instability

diagnosis

tests

treatment

patient outcomes