Out-of-range alignment linked with tibial component migration after TKA

David A. Crawford, MD

There is growing debate on whether TKAs should be aligned to a neutral mechanical axis or more patient-specific kinematic alignment. This study by Koen T. van Hamersveld, MD, and colleagues aimed to shed some light on this topic by evaluating tibial component migration and long-term aseptic survivorship of 85 cemented primary TKAs based on alignment relative to these two targets. At 10-year minimum follow-up, seven tibial components (8.2%) were considered loose and/or revised. None of the knees that were within 3° of a neutral mechanical axis (47 knees) had tibial loosening, whereas two tibial components were loose in constitutionally “in-range” knees (36 knees). Varus aligned knees had significantly more tibial component migration based on radiostereometric analysis.

While there are valid arguments for kinematic alignment, this study questions whether there may be a limit on alignment tolerances for long-term survival. One of the concerns with planning kinematic alignment with a varus tibial cut is overshooting that target by even a few degrees and placing the component in 6° or more of varus. The findings of this study may support the use of enabling technologies, such as robotics, to improve component and limb alignment, which ultimately may lead to better long-term survivorship, especially for those targeting kinematic alignment. It should be noted this study evaluated various implant manufacturers’ and component designs, which could confound the results.

David F. Scott, MD

Koen T. van Hamersveld, MD, and colleagues report a higher rate of tibial component migration in knees not aligned within ±3° of neutral TKA. Their analysis fails to account for native obliquity of the joint line as defined by the medial proximal tibial and lateral distal femoral angles, and the degree to which this unique individual anatomy was or was not replicated. They admit they did not follow kinematic alignment techniques. So, it is not logical to apply their results to the results produced/expected with kinematic alignment.

Ritesh R. Shah , MD

I read with great interest this study regarding the effect of coronal alignment on tibial component migration after TKA. 

As orthopedic surgeons, we know that obtaining neutral coronal limb alignment during TKA has traditionally been considered optimal for implant longevity, outcomes and function. Among other studies, we previously published results showing only 70% of individuals had neutral alignment; the obvious question that arises is whether aiming for neutral limb alignment or constitutional limb alignment should be the goal. Some studies show no difference in survivorship between neutrally aligned TKA compared with knees aligned in greater than 3° varus and valgus. Innovatively, this study uses radiostereometric analysis from three studies to evaluate implant migration comparing neutral mechanical limb alignment vs. constitutional alignment after TKA.

The authors conclude that out of range mechanical limb alignment leads to a higher rate of tibial component migration with the highest rate of migration occurring in mechanically varus TKA and no migration seen in mechanically neutral TKA. Although it is difficult to estimate premorbid constitutional alignment, when matching constitutional alignment, this study shows no difference in component migration if placed in mechanical neutral, varus or valgus. Further, although there are limitations to the study, including using only static coronal alignment measurements and lack of correlation between radiostereometric analysis (RSA)-evidenced tibial component migration and clinical symptomatology, previously published evidence has shown that RSA analysis demonstrating excessive tibial component migration is predictive of late aseptic loosening.  Thus importantly, when considering preventing late aseptic loosening, this study helps guide surgeons to aim for neutral when using mechanical limb alignment and specifically avoid varus.