Preoperative factors associated with extension gap in cruciate-retaining total knee arthroplasty: A retrospective study on continuous determination of distraction force.

Background: The aim of this retrospective study was to identify the preoperative patient-related factors affecting the soft tissue balancing in cruciate-retaining total knee arthroplasty. This is an important clinical issue, as the acquisition of adequate soft tissue balancing is essential for successful outcomes.

Methods: The study group included 59 knees treated for medial compartment osteoarthritis. The extension gap was measured using the newly electric tensor that enables continuous quantification of a distraction force ranging from 0 to 40 lbf. We performed regression analyses to identify the relationship between preoperative factors and the extension gap.

Results: Patient height, weight, and percent mechanical axis showed univariate correlation with the extension gap of either 30 lbf or 40 lbf. In the multivariate regression analysis without encountering multicollinearity, percent mechanical axis was inversely associated with the extension gap (t-value = -2.31, p = 0.02 for 30 lbf; and t-value = -2.39; p = 0.02 for 40lbf) as a significant independent factor.

Conclusions: We revealed the significant influence of several factors on the absolute value of the extension gap. Particularly, the severity of preoperative coronal alignment was a statistically independent explanatory variable, and the extension gap was overvalued in knees with severe varus deformity. This influence should be considered when comparing different individual cases longitudinally. Our feasible strategies could lead to a better understanding about the soft tissue balancing in total knee arthroplasty.