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Computation simulation shows tuberosity medialization decreases patellar lateral maltracking
Tibial tuberosity medialization decreased patellar lateral maltracking and patellofemoral contact pressures; however, it increased medial contact pressure, according to a computational simulation model. Anteromedialization compared with medialization decreased the risk for elevated postoperative contact pressures.
“The simulations indicate that tibial tuberosity medialization produces the desired decrease in lateral patellar maltracking associated with patellar instability,” John J. Elias, PhD, told Healio.com/Orthopedics. “Tuberosity medialization also shifts the patellofemoral pressure distribution medially, which is a concern for patients with medial cartilage degradation following patellar instability. The study identified a low level of preoperative lateral patellar tracking as the primary parameter related to elevated postoperative pressures.”
Elias and colleagues used six multibody computational simulation models that represented knees being treated for patellar instability to simulate dual limb squatting. Tibial tuberosity medialization was represented with patellar tendon attachment points on the tibia medialized by 10 mm. Investigators applied an additional 5 mm of anteriorization for anteromedialization. They used discrete element analysis to quantify the patellofemoral contact pressure distribution. Repeated measures analysis of variance with post-hoc tests and linear regressions were used to analyze data.
Results showed the tibial tuberosity medialization and anteromedialization significantly decreased the bisect offset index for nearly all flexion angles up to 80º, with the largest changes occurring near full extension. Tibial tuberosity medialization and anteromedialization significantly reduced the maximum lateral pressure at 55° of flexion. However, the procedures increased the maximum medial pressure from 30° to 80°. There was a significant association between the preoperative to postoperative increase in maximum contact pressure and the maximum preoperative bisect offset index for tuberosity medialization. However, this was not the case for anteromedialization. – by Monica Jaramillo
Disclosures: Elias reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
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Anteromedialization of the tubercle creates less medial load on the patella than straight medialization. Medialization and anteromedialization are commonly performed for patella maltracking, but the precise biomechanical effects on patients with patella instability are unknown. Elias and colleagues developed computational models derived from high-resolution MRIs of patella instability patients with an average TT-TG distance of 11 mm and performed medialization (10 mm) and anteromedialization (+5 mm anterior) procedures. Not surprisingly, both procedures improved tracking of the patella and unloaded the lateral patellofemoral joint, but also increased the load on the medial side. Anteromedialization created less elevation of medial contact pressures than straight medialization.
One limitation of the study is that 10-mm medialization was large given the minimally elevated TT-TG, and a lesser amount of medialization may be able to avoid some of the unintended medial increase. Clinically, this suggests that medialization can create significant medial pressure increases and if there is medial patella chondrosis (which can be common in instability or maltracking patients), then anteromedialization might be a better choice
NorthShore University HealthSystem
Director, NorthShore Orthopaedic Institute
Evanston, Illinois
Clinical Professor, University of Chicago Pritzker School of Medicine
Adjunct Professor, Northwestern University McCormick School of Engineering