Maximizing Tibial Coverage Is Detrimental to Proper Rotational Alignment

Abstract

Background Traditionally, the placement of the tibial component in total knee arthroplasty (TKA) has focused on maximizing coverage of the tibial surface. However, the degree to which maximal coverage affects correct rotational placement of symmetric and asymmetric tibial components has not been well defined and might represent an implant design issue worthy of further inquiry. Questions/purposes Using four commercially available tibial components (two symmetric, two asymmetric), we sought to determine (1) the overall amount of malrotation that would occur if components were placed for maximal tibial coverage; and (2) whether the asymmetric designs would result in less malrotation than the symmetric designs when placed for maximal coverage in a computer model using CT reconstructions. Methods CT reconstructions of 30 tibial specimens were used to generate three-dimensional tibia reconstructions with attention to the tibial anatomic axis, the tibial tubercle, and the resected tibial surface. Using strict criteria, four commercially available tibial designs (two symmetric, two asymmetric) were placed on the resected tibial surface. The resulting component rotation was examined. Results Among all four designs, 70% of all tibial components placed in orientation maximizing fit to resection surface were internally malrotated (average 9°). The asymmetric designs had fewer cases of malrotation (28% and 52% for the two asymmetric designs, 100% and 96% for the two symmetric designs; p \ 0.001) and less malrotation on average (2°and 5°for the asymmetric designs, 14°for both symmetric designs; p \ 0.001). Conclusions Maximizing tibial coverage resulted in implant malrotation in a large percentage of cases. Given similar amounts of tibial coverage, correct rotational positioning was more likely to occur with the asymmetric designs. Clinical Relevance Malrotation of components is an important cause of failure in TKA. Priority should be given to correct tibial rotational positioning. This study suggested that it is easier to balance rotation and coverage with asymmetric tibial baseplates; clinical research will need to determine whether the observed difference affects patellar tracking, loosening rates, or the likelihood of revisions after TKA.

Which Tibial Tray Design Achieves Maximum Coverage and Ideal Rotation: Anatomic, Symmetric, or Asymmetric? An MRI-based study

“…Our results with regard to tibial surface coverage are consistent with those found by Wernecke et al and Martin et al, who performed studies with a similar methodology for symmetric and asymmetric trays [9,11]. Dai et al investigated anatomic, symmetric, and asymmetric trays in multiple ethnicities for healthy knees [10].…”

“…Proper tibial rotation avoids excess risk of MCL tension [2], contact stress [3], knee pain [4,5], stiffness [6], and patellofemoral complications [7,8]. Different tibial tray designs offer varying potential in optimizing the relationship between tibial surface coverage and rotation [9]. An anatomic tibial tray was recently developed in an effort to better match patient anatomy compared to symmetric and asymmetric trays.…”

Rotational alignment of tibial components in mobile-bearing TKA: posterior substituted vs. PCL retaining

“…Some surgeons use an asymmetric component and maximize tibial coverage to obtain the best stability and load transfer [45,46]. Additionally, Martin et al [47] recently reported that it is easier to balance rotation and coverage with asymmetric tibial base plates than symmetrical tibial designs, which were evaluated in the current study. The strengths of this study include that all patients were treated by a single experienced surgeon, and that comparisons were conducted between PCL-retaining and PCL-substituting mobile-bearing designs.…”

Retrospective study of asymmetric vs symmetric tibial plates and ultracongruent vs posterior stabilized inserts in Indian population: An Indian experience of Natural Knee II

“…Most studies 13,14 which demonstrate the superiority of asymmetric tibial base plates over symmetric tibial base plates have not been done on cases of post knee replacement patients, but they have been done on hypothetical computer generated models of anthropometric western tibia; ignoring the fact that the tibial base plate has to be implanted matching the external rotation of the femoral component. External rotation of the femoral component differs from patient to patient and population to population.…”

“…12,13 Traditionally, it has been proposed that maximizing tibial coverage to increase fixation by improving load transfer from the implant to the proximal tibia avoids subsidence and loosening. 14 Asymmetric tibial trays are claimed to be more anatomic in nature and therefore cover the tibial plateau more completely than symmetric tibial trays 15 ; thus decreasing the incidence of tibial tray overhang and subsidence. However, tibial coverage rarely exceeds 78% and several authors have proposed a minimum of 75% coverage for adequate fixation.…”