BLOG: Indications change for anteromedialization tibial tubercle osteotomy
Since describing anteromedialization tibial tubercle osteotomy for realignment and unloading of the patella in 1983, indications have changed.
Publications have consistently demonstrated the efficacy of the procedure including Stephen A. Klinge’s 2019 study showing sustained good results and avoidance of arthroplasty at minimum 15-year follow-up after anteromedialization tibial tubercle osteotomy (AMTTO). To some extent, this seems logical – optimize patella tracking and lift it up a little to unload it. We showed this in biomechanical studies back in 1990.
But now, with 3D prints of dysplastic knees, we can see there is another reason why anteromedialization is important. Dysplastic trochleas curve laterally to meet a lateral tracking patella – essentially opening the trochlear door laterally (see Figure 1) 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. Anteriorization tips it up and unloads the vulnerable distal pole.
We now understand, in 3D studies at Yale University with Kristin E. Yu, Daniel R. Cooperman, MD, William McLaughlin, MD, Brian G. Beitler and Christopher Schneble, MD, that the patella and trochlea appear to be congruous in dysplastic patellofemoral joints, the patella often riding along the lateral condyle with a foreshortened medial facet, but nonetheless congruous. Moving the patella anteromedially (less than 50% of my recurrent patella instability patients) in patients with a lateral tracking vector 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 progressive articular breakdown.
As we understand this more fully with the help of 3D imaging, we realize that trochleoplasty may be best employed to remove the proximal aspect of medial ridge (as described in osteologic detail by Yu), when a tibial tubercle is moved distally and/or medially. My primary indication for trochleoplasty currently is in conjunction with a distalizing and medializing tibial tubercle transfer, with a goal of flattening the proximal medial ridge (to allow smooth entry of the patella into the trochlea).
These guidelines are similar to those of David R. Diduch, MD, but the only deepening is recession of the medial ridge, whereas the articular congruity of the trochlea is maintained as no deepening is done laterally. This can generally be done arthroscopically.
Our observations have been also that the more lateralized patella on a flat (Dejour B) proximal trochlea tracks rapidly across the proximal trochlea, in a congruent fashion, to engage the deepening trochlea more medially. Medial or anteromedial tibial tubercle transfer helps get the patella to the deeper trochlea sooner and therefore reduces or eliminates risk of lateral dislocation in such patients without need for trochleoplasty.
Trochleoplasty is not generally necessary at the time of AMTTO in patella instability surgery. Adding anteriorization and a little distalization to the TTO facilitates bypass of the less prominent or flat proximal ridge – a more common situation. This explains why Fotios Paul 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 help us to understand why Joseph N. Liu, MD, and Beth E. Shubin Stein, MD, had consistently good results with MPFL reconstruction alone for treatment of trochlea dysplasia in patella instability patients who did not have lateral tracking or need for TTO. Our observations currently, using 3D prints, suggest a proximal medial ridge spur recession trochleoplasty in conjunction with AMTTO in cases with a prominent proximal medial ridge spur and little need for deepening in the presence of a flat proximal trochlea when the patella can be maintained in a stable congruous relationship with the flattened trochlea by MPFC reconstruction (MPFL or MQTFL) and tibial tubercle transfer when appropriate to optimize alignment.
References:
Fulkerson JP, et al. Am J Sports Med. 1990;doi: 10.1177/036354659001800508.
Klinge SA, 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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