BLOG: Anteromedialization TTO is important in some patella instability surgery
Since describing anteromedialization tibial tubercle osteotomy for realignment and unloading of the patella in 1983, I have done about 1,500 anteromedial tibial tubercle transfers.
Publications have consistently demonstrated the efficacy of the procedure including our most recent one showing sustained good results and avoidance of arthroplasty at minimum 15-year follow-up. To some extent, this seems logical. Optimize patella tracking and lift it up a little to unload it. We showed this in biomechanical studies in 1990.
But now, with 3D prints of dysplastic knees, we can see that there is another reason why anteromedialization is important. Dysplastic trochleas curve laterally to meet a lateral tracking patella, therefore, essentially opening the trochlear door laterally (Figure) where the patella is sitting and waiting in extension. Then, the patella can engage into the trochlea and the result is a curvilinear path for the patella as the trochlea holds onto the patella and brings it medially, deeper into the trochlea in flexion, and a little lateral again further into flexion.
This puts a different twist on our understanding and sometimes behooves us to help the patella get medial into the dysplastic, curved trochlea so it can remain stable permanently and stop recurrent patella dislocations and optimize focal loads, with the additional help of medial patellofemoral reconstruction.
We now understand, in 3D studies at Yale University with associates Kristin E. Yu, BA, Daniel R. Cooperman, MD, and Christopher A. Schneble, MD, that the patella and trochlea are congruous in dysplastic knees, the patella often riding along the lateral condyle with a foreshortened medial facet, but nonetheless congruous. Moving the patella anteromedially in patients with a lateral tracking vector (less than 50% of my recurrent patella instability patients) should enable the patella to engage into the dysplastic trochlea more securely, lift up the distal pole to further facilitate engagement and also unload the distal patella articular surface to minimize and hopefully prevent articular breakdown. Further studies are needed with articular cartilage reproduction.
As we understand this more fully with the help of 3D imaging, we realize that trochleoplasty should be rarely needed as it inevitably decreases congruity. My primary indication for trochleoplasty currently is in conjunction with a medializing tibial tubercle transfer, only to flatten the proximal medial ridge (a spur that might touch the medialized patella). Even this is typically avoided, however, by adding some anteriorization and a little distalization to the tibial tubercle osteotomy (TTO) to bypass the proximal ridge.
This explains why Fotios P. Tjoumakaris, MD, and James P. Bradley, MD, had such consistently good results in their study of anteromedial TTO, with slight distalization, in athletes. These insights with 3D also help us to understand why Liu and Shubin Stein had consistently good results with MPFL reconstruction alone for treatment of trochlea dysplasia patella instability patients who did not have lateral tracking or need for TTO.
References:
Fulkerson JP, et al. Am J Sports Med;1990;doi:10.1177/036354659001800508.
Klinge S, et al. Arthroscopy. 2019;doi:10.1016/j.arthro.2019.02.030.
Liu JN, et al. Am J Sports Med. 2018;doi:10.1177/0363546517745625.
Tjoumakaris FP, et al. Am J Sports Med. 2010;doi:10.1177/0363546509357682.
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