treatment. Here are my disclosures. So borderline dysplasia is a major controversy in hip preservation. There's more consensus on the truly dysplastic hip needing a PAO, often now with arthroscopy. But in borderline dysplasia, some patients appear to need PAO and some patients appear to need hip arthroscopy. Choosing those correct patients is the challenge. So what is it? Borderline dysplasia is not a single hip morphology. It's a variable morphology. The anterior lateral posterior coverage can be much different across hips with the potential for hip instability. This is based on the lateral center edge, so traditionally 20 to 25 degrees. Some people use 18 to 25 degrees for a basic lateral center edge measurement definition. The risk of OA is just not in the truly dysplastic hip. It does extend into this borderline range from natural history studies from Europe. So borderline alone, it's controversial as a term. Maybe it's not the best term. Transitional estabular coverage pattern has been something that's been popularized a little more recently. So borderline dysplasia exists sort of as this transition between the truly dysplastic hip and normal. This is a common scenario. We just published this in OGSM, 20% prevalence in males and females. Female athletes, the prevalence may be even higher. This Utah study shows 46% of female athletes had borderline dysplasia. So we need to define the morphology and the setting of borderline dysplasia laterally. That's pretty easy, but it's more difficult anteriorly and posteriorly. We also not only need to think of the socket, but as the femur kind of combining it all with our femoral version to make our decisions. So looking at the anterior and posterior walls with the anterior and posterior wall index can help some. Really scrutinizing these walls, I think, is often more helpful than an anterior center edge angle. Here are some examples showing that anterior wall gets very undercovered in the setting of dysplasia. The low-dose CT has really changed hip preservation. We're really looking at structural diagnosis, and this is no exception here. We looked at 70 borderlines, showing how variable the anatomy here is. So 12 o'clock lateral, it's a pretty tight range. If you go anteriorly at 2 or 3 o'clock or posteriorly at 10 or 9, it's extremely variable. Lots of undercovered hips, lots of normal hips, lots of overcovered hips. So it can be really all over the place. So here's two examples of a nearly normal hip on the left in the borderline group, and then one with significant deficiency. This is a radiograph with, similarly, if you look for that anterior wall, it's almost missing. It's way up on the top of the head. And if you look at CT, you can see almost the entire head. This is a significantly dysplastic hip. So what factors guide treatment decisions? I think we really need a comprehensive evaluation that's history, physical exam, and imaging. So these are two hips in the borderline range that they can have instability or they can have impingement or they can have both. And the challenge is deciding between our treatment options of isolated hip arthroscopy versus the PAO, which we often combine with arthroscopy in this setting. The problem is the literature is somewhat weak in this topic. We don't have comparative literature. Shane and Andrea will hit on this as well. But we don't have great evidence to guide these treatment decisions. When I look at the literature, it's clear that our hip arthroscopy works in a lot of these patients. But a subset of patients appears to have suboptimal outcomes. When we look at the PAO literature, which is growing, we looked at a series at WashU of over 150 hips and well-selected hips. These hips do really well, 5% failure rate. So these are even better than what we might quote our FAI patients. Here's a typical patient, a young patient can recover really well from PAOs. It's not anything to be afraid of. Here she'll tell us briefly. Okay, so can you tell us about your recovery from your hip scope PAO surgery compared to the surgery you've been through before? This was a lot easier than my last surgery's recovery. Before the surgery, my pain would be like at a six or a seven. And this was after my hip scope, too, like I never got down from a six or a seven. So this has just been like a breath of fresh air after the surgery. So a happy hip will recover really well if the right surgery's chosen. The challenge is there's a lot of things to think about, from deformity characteristics, all those things listed here, to patient characteristics to make this decision. You want to think of where this patient is on that bell curve of instability to impingement. We've looked at this at WashU, finding key factors predicting diagnosis, acetabular inclination among the most important, as well as the inter-center edge alpha angle and IRF. This was based on two-dimensional things. We subsequently expanded that to 3D alpha angles, femoral version, acetabular coverage at one o'clock, driving decisions, which sort of makes sense in our hands that during this study period, it was about a 60% non-instability, 40% instability breakdown. Ideally, we want to develop tools that can assist with this. We're working on this borderline hip instability score that takes a number of factors, combines them in an easy clinical calculator to help us put these patients on our bell curve, that we may all have different cutoffs for this decision making, but quantifying this can really be helpful in the future. So if we come back to these things, I think these ones in yellow are maybe the most important in my mind. Inclination, 3D coverage, femoral version, we really want to know those, gender, soft tissue laxity, as Mark showed, and range of motion, really important to make these decisions. So I'll skip this quickly because we've read that, and we'll move on to the next sort of series.

borderline dysplasia

hip preservation

hip instability

diagnosis and treatment

periacetabular osteotomy