Abstract
The optimal force applied during ligament balancing in total knee arthroplasty (TKA)
is not well understood. We quantified the effect of increasing distraction force on
medial and lateral gaps throughout the range of knee motion, both prior to and after
femoral resections in tibial-first gap-balancing TKA. Twenty-five consecutive knees
in 21 patients underwent robotic-assisted TKA. The posterior cruciate ligament was
resected, and the tibia was cut neutral to the mechanical axis. A digital ligament
tensioning tool recorded gaps and applied equal mediolateral loads of 70 N (baseline),
90 N, and 110 N from 90 degrees to full extension. A gap-balancing algorithm planned
the femoral implant position to achieve a balanced knee throughout flexion. After
femoral resections, gap measurements were repeated under the same conditions. Paired
t-tests identified gap differences between load levels, medial/lateral compartments,
and flexion angle. Gaps increased from 0 to 20 degrees in flexion, then remain consistent
through 90 degrees of flexion. Baseline medial gap was significantly smaller than
lateral gap throughout flexion (p <0.05). Increasing load had a larger effect on the lateral versus medial gaps (p <0.05) and on flexion versus extension gaps. Increasing distraction force resulted
in non-linear and asymmetric gap changes mediolaterally and from flexion to extension.
Digital ligament tensioning devices can give better understanding of the relationship
between joint distraction, ligament tension, and knee stiffness throughout the range
of flexion. This can aid in informed surgical decision making and optimal soft tissue
tensioning during TKA.
Keywords
robotic-assisted - total knee arthroplasty - ligament balance - ligament tension
