The intraoperative gap differences due to joint distraction force differences in total knee arthroplasty are affected by preoperative lower limb alignment and body mass index

Background: Soft tissue balance is important for a good clinical result in total knee arthroplasty. Nevertheless, the appropriate evaluation of the intraoperative gap has not been established. We investigated the relationship between physical characteristics and gap differences due to distraction force, in order to determine whether intraoperative adjustment of the distraction force can be considered based on the physical characteristics of the patient.Methods: A total of 115 varus knees in which primary total knee arthroplasty was performed were retrospectively evaluated. The component gaps were measured under 60 and 80 N. The gap difference under 60 and 80 N was calculated. We performed a linear regression analysis to determine the correlation between the gap differences and patient parameters.Findings: Each gap was significantly larger under 80 N than under 60 N. The component gap difference is larger in the lateral compartment than in the medial compartment at each knee flexion angle. The gap difference nega-tively correlated with preoperative hip-knee-ankle angle at a knee flexion of 0 degrees and 120 degrees (r =-0.21,-0.19; p = 0.02, 0.05) and positively correlated with BMI in the lateral compartment at a knee flexion of 90 degrees (r = 0.31, p < 0.001).Interpretation: The difference in the intraoperative gap due to the joint distraction force was affected by the preoperative HKA axis angle and the body mass index in the lateral compartment. Surgeons should consider the effect of preoperative limb alignment and body mass index in interpreting intraoperative gap measurement.

Automated summary

The study found that key factors affecting the intraoperative gap difference include preoperative hip-knee-ankle angle and patient's body mass index, especially in the lateral compartment of the knee.