Summary

The use of robotic-assisted total knee arthroplasty (TKA) suggests improved component alignment and accuracy than when done using conventional methods. Does this have an effect on joint laxity? Our investigation of six pairs of knees demonstrated smaller changes in relative internal/external and valgus rotations in robotic-assisted TKA knees when observing laxity at discrete flexion angles.

Abstract

Purpose

The suggested improved accuracy of implant positioning with robotic assisted surgery for total knee arthroplasty (TKA) is seen as a benefit towards positive clinical outcomes. However, how the suggested improvements in alignment translate to affect joint biomechanics remains to be investigated. Therefore, this study aims to characterize post-procedural biomechanics through laxity testing following robotic-assisted and conventional TKA. We hypothesize that robotic TKA will yield more consistent laxity limits than conventional counterparts.

Methods

Six pairs of knees were used in this study. For each pair, one joint replacement was done using conventional methods while the second employed a VELYS robotic-assisted solution (DePuy Synthes). All TKAs were performed by the same surgeon and used a cruciate retaining rotating platform (CR RP) implant system. The knees were mounted onto a VIVO joint motion simulator (Advanced Mechanical Technologies Inc.). Once installed, specimens underwent a baseline lading scenario that involved flexing the knee from 15 to 90 degrees under a constant 30 N axial load while all remaining degrees of freedom were left unconstrained. Then, at discrete flexion angles of 15-, 30-, 60- and 90-degrees laxity limits were assessed via: (1) internal/ eternal (IE) torques of 4 Nm, (2) abduction/ addition (AA) torques of 8 Nm and (3) anterior/ posterior (AP) forces of 40 N and 80 N respectively. All limits were adjusted with respect to joint position during baseline to mitigate any mounting biases and account for specimen-specific joint behavior.

Results

External rotation laxity trended greater in conventional TKA knees than robotic TKA with the difference increasing with higher flexion, ranging from 13.7 mm ± 6.4 mm [conventional] and 13.6 mm ± 4.3 mm [robotic] at 15 degrees flexion to 25.6 mm ± 9.7 mm [conventional] and 18.8 mm ± 5.7 mm [robotic] at 90 degrees flexion. The same increased laxity though higher flexion in conventional TKA knees was also seen in anterior translation, however this was contrasted by greater posterior laxity robotic TKA specimen. At 60 degrees of flexion, all laxity limits we similarly observed that all laxity limits were lesser in robotic TKA knees in all degrees of freedom apart from varus rotation (5.4° ± 2.1° [conventional], 6.2° ± 3.6° [robotic]) and posterior translation (9.5 mm ± 2.1 mm [conventional], 11.5 mm ± 3.8 mm [robotic]).

Conclusion

We observed smaller changes in relative IE and valgus rotation in robotic TKA knees compared to conventional ones. Only at 60 degrees of flexion was the same true for anterior translation. Our current results suggest that differences in component alignment and fit of a robotic TKA knee could result in improved mid-flexion joint stability.