Hi, my name is Adam Yankie from Rush University, and I'm talking on when an NPFL is enough to treat patellar instability versus when a tibial tubercle osteotomy should be added. Please find other information on my website listed here. Tibial tubercle osteotomies add to the risk and recovery related to treatment of patellar instability and should only be utilized when absolutely necessary. Most commonly, tibial tubercle osteotomies are recommended in the setting of revisions, patients with cartilage damage and pain related to that, as well as patients with significant abnormalities. This last group is one of the most important groups to understand what are the best indications possible and what is the definition of significant. In general, the two factors you can correct with a tibial tubercle osteotomy are patella alta as well as tuberosity lateralization. We'll spend some time looking at what factors play a role in recurrent instability versus failure of NPFL reconstructions with regards to tibial tubercle alignment in these two factors or planes. When looking at first time patellar dislocations, Dom et al evaluated the effect of patella alta as well as other factors, including dysplasia and age under 25, to look at the risk of recurrence over a period of several years. When looking at these results in summary format, we see that when you have no alta dysplasia and are older than 25 years old, your risk of recurrence is 8.6%. If you add alta to this patient population alone, your risk only increases 3%. Therefore, patella alta with trochlear dysplasia in patients over 25 is not what you would recommend as a significant risk factor for recurrence after a first time dislocation. If you have patients that are under 25 years old, that risk factor alone brings them to 26% risk for recurrent instability. If you add patella alta to that group, you increase their risk approximately 7%. Still not a particularly significant increased risk compared to their baseline risk. Finally, looking at patients with trochlear dysplasia under 25 years old have a 60% chance of recurrent instability. And again, adding alta to this setting only adds 10% risk. Therefore, age under 25 years old and trochlear dysplasia in this setting were more significant risk factors for recurrent patellar instability than alta in all other scenarios. Erin Critch and others evaluated the RIP score, which is for recurrent patellar instability. And their factors included tuberosity lateralization through the TT-TG-PL ratio, as well as the same age cutoff of 25 years old skeletal maturity, as well as de jure grading. Of note, they did evaluate patella alta and found that this did not remain significant in their risk calculator. In this setting, TT-TG on its own did not significantly increase someone's risk of instability if they are over 25 years old. However, it put them in a moderate risk group with age under 25 and TT-TG patellar length ratio greater than 0.5. When we then switch over to look at the outcomes of isolated MPFL reconstructions, it's important to understand what risk factors increase the failure rate of MPFL reconstruction and failure being defined as re-dislocation, as well as lack of subjective improvement or PRO failure. Only three studies evaluated risk factors with the outcome of re-dislocation being the outcome. And when patella alta was analyzed, only one of the two studies found it to be a significant risk factor for re-dislocation. When trochlear dysplasia was analyzed, two out of three papers found this to be significantly associated. This paper demonstrates the most factors that were controlled for across all studies, which were five factors. This found that all of the measurements associated with trochlear dysplasia remained significant. And when you controlled for these other factors, patella alta was no longer significant. These studies did not utilize tibial tubercle lateralization as one of their main risk factors. This slide evaluates PRO failure in a slightly busy, but it's important just to understand the overall trends evaluated here. Studies that did not control for certain factors are grayed out. If a factor was controlled for and found to be significant, there is a green checkmark. And if it was controlled for and not significant, the box is white. If we look at the bottom, this study only controlled for one factor, and it found TTTG position to be associated with failure of isolated MPFL. When we look at the top study, which controlled for the most factors, TTTG was no longer a significant factor when taking into account age at first time of dislocation, bilateral symptoms, as well as femoral tunnel placement. If we flip this and look at this based on the columns, half of the studies that evaluated trochlear dysplasia found it to be a significant risk factor for dislocation. However, almost all of these studies did not control significantly for other factors. Looking at TTTG measurements, half of the studies also demonstrated that this was a significant risk factor. However, again, most of them that showed that it was significant didn't control for as many factors except for the top study. Finally, looking at femoral tunnel placement demonstrated that all studies that evaluated tunnel placement showed that this was a significant risk factor, including the ones that controlled for the most factors. Therefore, it is crucial to do a correct MPFL anatomically, both on the patella and, in particular, on the femur, and that tibial tubercle placement is a risk factor but is not the only factor that is associated with outcomes and frequently is not associated with outcomes depending on a specific patient situation. If we then try to understand what the role of the lateral tuberosity is relative to the other factors that control patellar tracking, it's clear that there are global factors that have to do with overall leg alignment and local factors that have to do with patellar tracking at the knee itself. Tibial tubercle position crosses both of these boundaries as it adjusts how the patella tracks at the knee and also can adjust or overcorrect an area that has global abnormalities. Therefore, tubercle position may not be abnormal in a given patient, but overcorrection of it can compensate for abnormal global factors. We can also think about the role of the tibial tubercle position as the patella goes from full extension into flexion, eventually engaging in the trochlea. One of the initial goals of patellar tracking is to get the patella to align with the groove before it gets to the groove. Factors highlighted to the right are associated with these being correct. And here we can see the Q angle, understanding that anything that lateralizes the ASIS position or the tibial tubercle position increases the lateral force factor on the patella, increasing the risk of lateral dislocation. A clinical or MRI Q angle is essentially the TT-TG measurement, as this looks at the trochlear groove placement relative to the tibial tubercle placement. And this overlaid on top of each other gives you an idea of the amount of displacement in the coronal plane or the axial plane of these two factors as they span the knee. This is different than the TT-PCL measurement, which goes from the PCL fossa to the tibial tubercle and looks at lateralization of the tubercle itself relative to the proximal tibia to see if this is an actual structural abnormality at the tibia or is the TT-TG abnormal because of other factors, such as a medialized trochlear groove due to dysplasia. The second goal is to have the patella engage at the appropriate degree of knee flexion, which is almost solely related to patella alta. If we look at this example, a patient with significantly increased patellar height would require increased degrees of knee flexion to engage in the trochlea if one is present. This diagram demonstrates if you take a knee radiograph and highlight the area of the trochlear groove where it would normally engage at approximately 30 degrees of knee flexion and you add significant patellar height to this patient to get the same amount of engagement would require another 15 to 20 degrees of knee flexion. This increases the overall working length of the MPFL reconstruction and is the goal of a distalization of the tibial tubercle. Similarly, if you look at the length changes of the medial patella femoral complex, going from 0 degrees to 90 degrees and looking at length changes throughout that arc of motion, we've evaluated this at different patellar height measurements. And if you look at the midpoint of the patella, which is the orange line at the bottom, there's almost no significant anisometry from 0 to 90 degrees until you get to an ALTA measurement of 1.6. This change happens somewhere above 1.4. More drastically, if you look at the proximal aspect of the MPFC insertion on the quadriceps tendon, this is the blue line at the top. There's 15 millimeters of anisometry from 0 to 90 degrees at a CD ratio of 1. And this increases to 25 millimeters at a ratio of 1.6, constantly increasing along the way. Therefore, MPFL or osseous-based reconstructions potentially are more durable in the setting of patella ALTA. One other goal is that the patella needs to engage at the appropriate degree of knee flexion and also have something to engage with. If the patient has significant trochlear dysplasia, they may be engaging in their trochlea. But if a trochlea is not present that's concave, then it won't function to resist lateral patellar displacement. A final factor is that a patient needs to have good dynamic control of their lower extremity to decrease the likelihood of internal rotation of the femur, which also functionally will increase the lateralizing forces on the patella. All of the factors that we know increase risk for recurrence after non-operative treatment or isolated MPFL reconstructions need to be taken into consideration in all patients so that you're not surprised when a patient has a failure what might have contributed to their failure. None of these cutoffs are utilized as a firm cutoff for correction and more of a guideline that these factors may be concerning. We'll now evaluate these factors through two cases to help understand the role of a tibial tubercle osteotomy in patellar instability. The first case is a 14-year-old female who has bilateral patellar instability, no traumatic events or hemarthroses, and she can dislocate in extremely low mechanisms such as activities of daily living. She had prior bilateral arthroscopic lateral releases. On physical exam, we can see here on her unaffected leg that she has no significant J sign. On her right side, as she extends her leg, she has a significant J sign with a smooth transition that's approximately two quadrants. When we look at her hip rotation on her unaffected side, she has internal rotation to about 15 degrees. When we look at her affected side on the right, we see that her internal rotation is significantly increased to almost 50 degrees. Looking at her radiographs, she has signs of femoral anaversion on her standing AP x-rays, a type C trochlea, and a CDI ratio of 1.44. Mechanical axis demonstrates neutral alignment with a TTTG of 14.6 and TTPCL 22. She has no tibial torsion, 34 degrees of femoral anaversion, and she corrects through her knee rotation angle as her femur is significantly internally rotated relative to the tibia. Again, we can take all of these factors and then rank them into concerning and not concerning factors. If we use the prior criteria that we listed, she has increased femoral anaversion, increased patellar height, and her prior lateral release. Clinically, she had significant in-pointing of the patella, and this was affecting her overall gait, and it was recommended that she undergo a derotational osteotomy. She underwent derotational osteotomy over a intramedullary nail. Post-operative examination demonstrated on her unaffected side that she still had the same internal rotation, and on her operative side, her internal rotation decreased to approximately 15 degrees, matching her non-operative side. She unfortunately still had recurrent patellar instability after the derotational osteotomy, and due to her already having a significant surgery and outcomes and increased patellar height being associated potentially with failure, the patient was interested in a single-stage surgery that would have the lowest likelihood of recurrent instability, and because of those factors, we elected to proceed with a tibial tubercle osteotomy and NPFL reconstruction for distalization. However, without her prior history of surgery, she potentially could have undergone an isolated NPFL reconstruction. Her examination and anesthesia demonstrated significant patellar lateral tilt and eversion due to her prior release, as well as significant lateral and medial instability. Here we can see that as we flex her knee, she still has significant instability as she does not have normal patellar height. Arthroscopic examination demonstrated that she did have chondral damage that was able to be debrided. However, she had no pain complaints, and this was left in situ. She was treated with a distalizing tibial tubercle osteotomy with an NPFL reconstruction with hamstring allograft. Our final case involves a young patient with patellar instability and maltracking with no pain complaints. Here we can see a video of her trying to perform a squat, which is unable to be performed due to the significance of her J sign. And with her quadriceps contracting, she is not willing to let her patella locate in the trochlea as she flexes further. Here we can see examination on the table in a non-weight-bearing fashion with significant valgus, and we can see the jumping J sign as her patella relocates in the groove. This can be held in position with manual pressure as long as her quadriceps is not being activated. When we look at this from a lateral view, we can again see the engagement of the patella with flexion to approximately 45 degrees. This is similar to what we see on her radiographs, where she has significant distal femoral valgus, and we're looking at a lateral of her patella with almost an AP of the femur with her knee in full extension. As she flexes her knee, we can see that her patella engages centrally and is now facing forward. She has a significantly hypoplastic lateral femoral condyle that can be seen on her AP view as well as her PA. She has likely an unclassifiable grade of dysplasia with a supratrochlear spur and a patellar height of 1.2 on a CDI ratio. Her TTTG is three centimeters, and her TTPCL is 3.2 centimeters. Her 3DCT demonstrates that her, she has significant intraarticular dysplasia on the lateral tibial plateau due to her distal femoral valgus. Looking at rotation, she has no significant femoral anteversion, and in fact has some femoral retroversion with no tibial torsion. Again, we take all of these factors and try to take the ones that are the most concerning, which is her valgus, TTTG of three centimeters, as well as a severe J sign. It was discussed with the patient she could benefit from an MPFL reconstruction and a possible distal femoral osteotomy versus a tibial tubercle osteotomy to try to correct for her J sign in tracking. Examination and her anesthesia demonstrates she had significant valgus as well as a degenerative distal lateral femoral condyle on arthroscopic examination. When we performed our approach for a possible tibial tubercle osteotomy, it became very clear that if we rotated the tibial tubercle externally, this would accentuate her J sign, which is seen here, as she relocates at a higher degree of knee flexion. However, if we internally rotate the tibia and flex the knee as well, we now see much more smooth tracking with almost elimination of the J sign. Based on these findings, we did elect to perform a lateral lengthening as well as a tibial tubercle osteotomy given that her TTPCL and TTTG measurements were severely abnormal over 30 millimeters. We performed a very flat cut that was almost parallel to the floor with almost 10 degrees of anteriorization, and we translated this approximately two centimeters. After this was fixated, we then prepared our NPFL reconstruction so we could check length changes, finding that we had appropriate loosening and flexion of approximately 10 millimeters. After this was complete and we had found the shottles attachment on the femur and committed to the reconstruction, and the tibial tubercle osteotomy was fixated, we then took the knee through a range of motion and found that there was normal patellar tracking and elimination of the J sign. Arthroscopic examination demonstrated that the graft was extra articular as planned, and there was no signs of any patellofemoral overload or difficulty obtaining access to the joint. Post-operatively, the patient did extract Post-operatively, the patient did extremely well, and here we can see her performing a squat now and her patella staying antegrade and not dislocating in full extension, even given her significant distal femoral valgus. We can also see that she tracks centrally passively while supine, significantly improving her symptoms. Based on these findings, we still recommend that a tibial tubercle osteotomy is primarily indicated in the setting of revisions with abnormal anatomy, patients with cartilage or patellofemoral pain, and with patients with values significantly abnormal, which can be difficult to define, but are likely based on the guidelines listed before. Thank you very much for your time and attention.

tibial tubercle osteotomy

patellar instability

revisions

cartilage damage

patella alta

tuberosity lateralization