And I think it's appropriate to start with the assumption that the workhorse here is the MPFL reconstruction and the majority of these patients we can stabilize with a perfectly or an excellently performed MPFL reconstruction. David, thank you for inviting me, us, to speak and organizing all this. And you've asked me to talk about when to add a tuberosity osteotomy. I think many of us are comfortable with tuberosity osteotomies. There's so much that we can do, not necessarily to make the anatomy normal, but to compensate for other problems, things like anteversion and torsion and valgus alignment, Q angles and all that. So the question is, when do you add a tuberosity osteotomy? Think about our problem here as one of imbalance. So we know that maltracking is a deviation from the normal midline axis, and it's a balancing act between these three forces. And the clinical manifestation of the imbalance is what we see, this J sign. And John Fulkerson has taught us it's really important to keep all these forces in balance. And that's what we're trying to do is to improve the imbalance by adding a tuberosity osteotomy when indicated. So in this clinical study, the authors identified risk factors for recurrent dislocations. And of course, they found some of these anatomic risk factors that we're aware of. And we know if you've got these risk factors, you've got a higher risk of recurrent instability. What about the results of isolated NPFL reconstruction? Well, these authors found 10% or 5% of their cases that required revision. They identified these risk factors. These are reasons why an isolated NPFL reconstruction might fail and reasons to consider a concomitant osteotomy. In this study of 26 patients who underwent revision NPFL reconstruction, again, anatomic risk factors for failing. So decide what you're comfortable with, have some options available, and look at those isolated NPFL reconstructions. Ask yourself, how can I decrease the risk of failure by adding an osteotomy? In this study, the authors compared isolated NPFL reconstruction to a combined NPFL reconstruction and tuberosity osteotomy in patients who had a TTTG distance of 17 to 20. So normal to slightly elevated. And they found that at least the functional outcome scores and the patellar kinematics that they reviewed were improved when you added the tuberosity osteotomy. So if you look at this 3D dynamic CT scan, watching that patella maltracking, you'd have to ask yourself, how can I expect an isolated NPFL reconstruction to stabilize this patella? And am I asking too much of that soft tissue graft? Is this going to fail like if you have a varus knee and a varus thrust and you do an isolated soft tissue LCL reconstruction? And then when you look at this sort of combined maltracking and high-grade chondral lesion, and you keep in mind that with an NPFL reconstruction, the main force vector isn't directed medially, it's actually directed posteriorly. So you over-tighten that graft, you ask too much from that graft, and you increase the posterior directed forces, and then you can end up with high-grade chondral pathology like this. As Jackie pointed out, you have to be very careful about how you fix that NPFL, and don't ask too much from your NPFL graft. So when do you add a tuberosity osteotomy? We can look at some basic science data. We can try to understand using computational modeling, actual patients where models are created and then they're tested, demonstrating that, for example, this is a simulated dual limb squatting study. And in this case, when you added antramedialization to patients who were maltracking and you compared isolated NPFL reconstruction to combined NPFL reconstruction and AMZ, the combined patients had a decreased risk of maltracking postoperatively. So less likely to have subsequent instability. In this study where the tuberosity was lateralized, again, it's a simulated squatting model, so there's limitations to computational modeling. But the maximum graft tension, so the forces in the graft that leave you with that resultant posterior force vector, are correlated with the tuberosity position, but not with patella alter trochlear dysplasia. So the primary factor here was the position of the tuberosity. That's not always the case. But this is a suggestion that if you've got a lateralized tuberosity, consider normalizing that lateral force vector. So if we take that one step further and look at ALTA, one of the risk factors for maltracking patella ALTA, you use the Catan-Deschamps Index, the CDI, and really what you care most about is sagittal engagement. At what point is the patella brought into the trochlea so that the lateral trochlear ridge provides a structural support against lateral translation? We try to quantify this radiographically using the patella trochlear index, or the CDI, which is the easiest way to do it. In the simplest way of thinking about this, we can go back to that concept of the Q angle. The greater the lateral force vector, and it's based on a bunch of things, including the tuberosity position, valgus alignment, hip rotation, muscle strength, all of these things. But the greater that lateral force vector, the greater the risk of lateral translation, pathologic lateral translation. We try to quantify that using things like the TT-TG distance or the TT-PCL distance. You need some numbers. You need to be able to study this. You need to look at your CT scan or MRI, whatever you have access to, whatever resources you have, and develop in your own mind a threshold for where you decide it's necessary to add a tuberosity osteotomy. And remember that a lateralized tuberosity is a risk factor for developing arthritis, and it's shown in this study right here, even in patients without instability. So what stabilizes the patella? Well, we've got the dynamic muscle action, soft tissue restraints, and if that's the primary problem, then an MPFL reconstruction and add an osteotomy if you need to. The tuberosity osteotomy is something most of us are pretty comfortable with. There's a lot you can do with it. You can medialize. You can antramedialize if you want to unload a chondral defect. You can distalize if your patellofemoral joint has poor trochlear engagement. With an antramedialization, you decrease that Q angle and the TTTG distance in the lateral force vector, but you also decrease patellofemoral forces following the McKay principle. So you anterize the tuberosity. You elevate the inferior pole of the patella. Remember though that if you have a proximal lesion, you're increasing the proximal forces. You've got to think this through and individualize that osteotomy to the problem that your patient has. There are a bunch of ways to do distalizing osteotomies. You can take your shingle, move it distally based on the calculated distance that you need to achieve capture in the trochlea. Take that piece and move it proximally. This is a technique that I use and I've been using for many years. It seems to work pretty well. Here the shingle is released distally. With an AMZ or a medialization, you leave the periosteal hinge intact distally, but if you're doing a distalization, you can take that distal fragment, pack it proximally, stick a little bone graft in. Let me show you a case presentation. This is a 30-year-old woman. She had her first child eight months ago. She's had four dislocations on the right, one on the left. She has Charcot-Marie-Tooth. Here's her exam with the lower extremity weakness that you'd expect. Her radiographs here showing some calcification there and most notably patella alta. The CDI is 1.47. If you look closely on your sagittal MRI, there's an abnormal signal to the articular cartilage far distally on the patella. You try to measure out your sagittal engagement and you get this fairly low PTI. On the 3DCT, you can see how poor or how limited that engagement is, and yet her TTTG distance is in the normal range. Bisect offset's 100%. To summarize her radiographic workup, she's got a normal position of her tuberosity, patella alta, poor engagement. She's subluxed with a bisect offset of 100, and she's got the chondrolesion at the inferior pole of her patella. Her primary problem is soft tissue insufficiency. We're going to do an MPFL reconstruction to address that. She also has patella alta with poor engagement and a chondrolesion, and this neuromuscular disorder with lower extremity weakness. So we're going to do an MPFL reconstruction and then add a distalizing modified AMZ. It's a very powerful tool, and you just modify the way you do your osteotomy to achieve the goals of trying to improve the biomechanics. In this case, it's a 7-centimeter shingle here. There's the distal cut. There's the fragment. And I like to use three 3-5 bicortical screws. It seems to work well. Do your osteotomy first, and then do your MPFL reconstruction after you do your osteotomy. Remember about the complications. I think we should never talk about surgery without talking about potential complications. All of these things can happen with osteotomies. Of course. And I'm showing you a step cut osteotomy here. It's not the only way to do it. You have to be careful about distal healing. We looked at the risk of complications following distalizing and non-distalizing tuberosity osteotomies. It's a fairly low complication rate. The most common thing is delayed union. The vast majority go on to heal. And it's more common to have radiographic delayed union in distalizing osteotomies compared to non-distalizing osteotomies. Here's the same patient. Here are her postoperative x-rays at two weeks. At two months, she fell down. And if you look closely at the shingle, it's loose. The screws are still good. At four months, she's no longer tender. She's not symptomatic. The shingle appears to be healing. And when she came back at two years to have the other side done, the shingle's healed. Be aware of this with a distalizing osteotomy. There are ways to work around this. Just be patient and follow these radiographically and clinically. You do have a larger incision, a longer postoperative period, a higher risk of complications when you add a tuberosity osteotomy to your MPFL reconstruction. Here's a study that looks at return to sports. At any level, 93%. And the same level, 71%, looking at combined tuberosity osteotomy and MPFL reconstructions at an average of six and a half months, a very low rate of recurrent instability. The isolated MPFL reconstructions got back to sports at a higher non-statistically significant level than the combined osteotomy. Still at 87% getting back to sports. To summarize, in patients with normal alignment, the MPFL graft acts as a simple check rein. There should be little or no change in force during knee motion unless you've malpositioned your tunnels. In patients with a lateralized tuberosity, severe dysplasia, and especially concomitant alta, the graft carries an increased load. And you have to decide for yourself based on your resources and your understanding of what you're doing, at what point do you need to do something extra to unload that graft. And the TTO offers, I'm sorry, alters contact forces and improved maltracking more consistently than MPFL reconstruction alone, but of course increases the risk of overloading the cartilage if you put excessive forces on that graft. So the algorithm here to summarize, the mainstay here is MPFL reconstruction to stabilize the patella and not to realign it. If you need to realign and change forces, then add an osteotomy. Here are the common TTO osteotomies. Consider distalization. Consider take a close look at your cases and measure your patella height pre and post-operatively on your MPFL reconstructions. You'll find in some cases that you're distalizing with an isolated MPFL reconstruction and it's something that's dependent on your technique. I'll just mention that. Take a look at your cases, measure pre and post-operatively, and you'll realize that in some cases you're distalizing. And then these other osteotomies that our other speakers will talk about. So thanks very much.

tuberosity osteotomy

MPFL reconstruction

patellar instability

maltracking

recurrent dislocations