Thank you so much for having me. So the J sign is considered to be visual evidence of patellar maltracking. It was initially called out in relation to quote VMO deficiency and that term has fallen by the wayside. Originally it was linked to patellar tilt on imaging. I think now we have a little bit more granular understanding of other factors that might be contributing. There's a variety of severity. You can see on the left there, if you caught that, there's a smooth J sign. There's no, it's an obvious move, but there's no jump. And on the right, the patient had a really severe quote jumping J sign, obligatory dislocation and hyperextension. People have tried to quantify this or grade it. And there's a little bit of a variety in the literature. This is a recent option that came out in 2019 that's based on the quadrants of translation, which is attractive. It sort of passes the common sense test and I'll draw your attention to the grade three and grade four there as sort of the high grade J signs. But our dogma is not firm and you'll see some studies that say, you know, it's none versus any. You'll see some that try to say slight versus positive versus severe. And I think that dogma is partially not intact because we're not really reliable at quantifying the J sign. So there were two studies that came out of a meeting of the International Patella Ephemeral Study Group. So a group of people who really stare at J signs a lot and think very deeply about them. And we were not very reliable at quantifying the number of quadrants that that patella moves as the knee moves into extension. As compared to Andy Kazagiri's group of like dynamic CT, so relative to the bisect offset, very objective data. And then Laurie Heemstra in Canada took this a step further. She found that the inter-rater reliability was fair or moderate and was interestingly cited. But she had us come back in three months and try again on the same studies and found that the intra-rater reliability was poor. And that didn't matter whether we said no versus any J sign or a five point scale of none versus the number of quadrants. But there's something to this and I'll show you more data in just a minute. I think that as I go through this literature, one of the fatal potential flaws of both of these studies is that they were done on videos, right? People are meeting in a place and people are bringing videos of their patients. And so you're rendering this three dimensional exam to a two dimensional video. And I wonder if we would get different data in person. And I say that because there are a lot of studies now that call out the J sign as predictive. So it correlates with lateral patellar translation on CT. That sort of passes the common sense test. It's an independent predictor of MPFL reconstruction failure. I listed these in chronological order, but I'll draw your attention to the second to last study as another example of MPFL reconstruction failure that also called out patellar ALTA. You'll see more about ALTA in just a minute. The grade three or high grade J sign correlates with a lower PRO, so the Kujala score is one that we use a lot for patellar femoral outcomes. And then more MPFL graphed laxity post-op after MPFL with or without TTO. And then a high grade J sign predicts inferior outcomes if you're doing MPFL with derotational osteotomy. And then finally, J sign and BMI correlate with disease specific quality of life measurements. So it's an important factor. I don't think we can throw it out yet, and I think we need to study it better in order to understand the reliability of it. So it's an indicator of malalignment. And Zhang's group in China has shown us a lot in recent years about femoral antiversion. I think they get antiversion measurements on all of their patients as standard of care. And so they found that risk factors for a high grade J sign included femoral antiversion, external tibial torsion, and patellar ALTA. And then Zhao's group showed that it's closely associated, again, with patellar ALTA, but also dysplasia. The patellar ALTA argument is supported by this study in 2020, that 30 out of 31 J signs in the setting of Katondashamp over 1.25 resolved if you distillized that trochlea, or I'm sorry, the tubercle. So you bring that patella down into the group, that J sign resolves. And then in terms of femoral antiversion, Zhang's group showed us that MPFL reconstruction outcomes are inferior to MPFL plus distal femoral osteotomy, or sorry, derotational femoral osteotomy in the setting of antiversion greater than 30 degrees. And this effect is especially amplified if they have a high grade J sign going into surgery. And then there's trochlear dysplasia. The elephant in the room, it's always coming up. It's the common denominator in terms of the most common anatomical factor present in patellar femoral instability. It's the strongest predictor of recurrence in multiple studies of first timers and recurrent dislocators. The problem is trochlear dysplasia measurements are also not particularly reliable in terms of inter-rater and intra-rater reliability. And I'll draw your attention here to the supratrochlear spur or bump. I think that's getting more attention. You probably heard from Dave Dedeck if you attended the session yesterday about that piece in particular acting as a launch ramp of that patella into the gutter rather than the groove. So you've heard about the Jupiter cohort. It's a study, a multicenter study of multiple sites. We have over 2,000 patients enrolled, and the imaging has proven to be a major rate limiting step. As you might imagine, there's a lot of reads. We want our musculoskeletal radiology experts to be reading them. And so we're currently recruiting more radiologists to help because ours are overwhelmed and they're doing a fantastic job. So knowing that we had more numbers than these previous studies that I showed you, we grabbed the first 319 patients who had completed reads at the time that we pulled the data. And we asked what factors correlate with the presence of a J sign. And interestingly, on physical examination, not much correlated, but effusion did. I found myself wondering if that was a chicken versus an egg thing. And then patellar translation did. And patellar translation made us look more at ligamentous laxity. And though the Baton score itself, so generalized ligamentous laxity, did not correlate with the presence or absence of a J sign, if you take out knee hyperextension alone, 69% of patients with knee hyperextension had a positive J sign, resulting in a 13 times odds ratio. So if you think about that ALTA equation, and then you add hyperextension, maybe even if their Catan-DeChamps doesn't qualify, are you creating kind of a functional ALTA? And then on imaging, no variables reach significance except for patellar articular length, which is the denominator in our measurement of patellar height. Our favorite one is Catan-DeChamps. And you probably learned from Liza Arendt yesterday, if you attended the session, that the relationship of the patella to the femur probably matters more in the understanding of ALTA than the patella to the tibia, the patella to the tubercle, to the patella to the joint line. So if you imagine a short patella and a trochlea that gets a little too shallow too soon and maybe a little hyperextension of the knee, then maybe you're creating this functional ALTA that we're all so worried about. And then I can't officially call this out yet because it didn't achieve significance, but the only one that came close besides that patellar articular length was the trochlear bump. And so I found myself wondering if we pull this data again once we have 2,000 patients, are we going to see that bear out as a trochlear dysplasia marker that does have good inter-rater reliability? So the J sign is multifactorial. I don't know what to do with the effusion piece, but we'll keep it in mind as we continue to study this. It's an indicator of malalignment, patella ALTA being sort of the strongest factor to emerge from all this literature. Femoral antiversion, it isn't covered well in all of the Jupiter patients. We didn't consider rotational studies to be standard of care. And so it'll be a better study when we have more to pull there in terms of the people that we were suspicious on physical exam. Trochlear dysplasia is always on the list, and we'll keep an eye on that trochlear bump in particular. And then ligament dyslaxia, but particularly knee hyperextension. So I would put to you, especially based on this Jupiter data, that the thing that you're seeing as movement from medial to lateral is really a multifactorial phenomenon that involves rotational anatomy and it involves the height of the patella, and so we need to consider this as we consider our interventions for these patients. I have to thank Bob Magnuson for his inception and Brilliant Methods for this study, Beth Schubenstein for her perspective and ongoing mentorship, Shital Parikh for keeping us honest on the reliability of these measurements, and then the rest of the Jupiter investigators and the research team for their ongoing discovery. Thank you so much.

J sign

patellar maltracking

VMO deficiency

patellar tilt

lateral patellar translation