Recently published results showed large variation in the rotational plane for both femoral and tibial components during 3-D unicompartmental knee arthroplasty component alignment analysis in the standing position, suggesting the importance of component positioning.
Researchers used a biplanar X-ray imaging acquisition system to image 77 metal-backed fixed-bearing medial unicompartmental knee arthroplasties (UKAs; Zimmer) in 68 consecutive patients in the standing position. To determine component position and contact location, researchers imported the UKA models into a virtual imaging environment and registered the models with a component silhouette on an X-ray image. Researchers digitized anatomic bony landmarks of the lower limb for quantification of the bone alignment.
Results showed a 3-D UKA component alignment of approximately 1.6° valgus for the femoral component and of approximately 3.9° varus for the tibial component, as well as approximately 6.5° external rotation for the femoral component and approximately 4.4° internal rotation for the tibial component. Researchers found component flexion of approximately 2.4° for the femoral component and 5.1° posterior tibial slope for th tibial component.
The average contact point was located medially and posteriorly by approximately 7.8% and by 0.7% of tibial component dimensions relative to its center, according to in vivo UKA articular contact analysis. Multiple regression analysis showed femoral component flexion significantly affected the UKA anterior/posterior contact position.
According to results, 38% of patients had ideal femoral component alignment and 35% of patients had ideal tibial component alignment when considering both varus/valgus and flexion/extension. Overall, 14% of patients had ideal UKA positioning while 42% of patients had malalignment of both components, researchers noted. – by Casey Tingle
Disclosures: Tsai reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.