Intraoperative joint gaps and mediolateral balance affect postoperative knee kinematics in posterior-stabilized total knee arthroplasty

• Gap difference of 135° − 0° correlated with lateral condylar posterior translation.
• Gap difference of 135° − 0° correlated with femoral external rotation.
• Gap difference of 135° − 0° correlated with maximum knee flexion.
• Well-balanced knees showed less medial condylar anterior translation.
• Well-balanced knees showed the most neutral valgus/varus rotation.

BackgroundAdjusting joint gaps and establishing mediolateral (ML) soft tissue balance are considered essential interventions for better outcomes in total knee arthroplasty (TKA). However, the relationship between intraoperative laxity measurements and weightbearing knee kinematics has not been well explored. This study aimed to quantify the effect of intraoperative joint gaps and ML soft tissue balance on postoperative knee kinematics in posterior-stabilized (PS)-TKA.MethodsWe investigated 44 knees in 34 patients who underwent primary PS-TKA by a single surgeon. The central joint gaps and ML tilting angles at 0°, 10°, 30°, 60°, 90°, 120° and 135° flexion were measured during surgery. At a minimum of two year follow-up, we analyzed in vivo kinematics of these knees and examined the influence of intraoperative measurements on postoperative kinematics.ResultsGap difference of knee flexion at 135° minus 0° was correlated with the total posterior translation of lateral femoral condyle (r = 0.336, p = 0.042) and femoral external rotation (r = 0.488, p = 0.002) during squatting, anteroposterior position of lateral femoral condyle (r = ‐ 0.510, p = 0.001) and maximum knee flexion (r = 0.355, p = 0.031) in kneeling. Similar correlations were observed between deep flexion gap differences with respect to the 90° reference and postoperative knee kinematics. Well-balanced knees showed less anterior translation of medial femoral condyle in mid- to deep flexion, consistent femoral external rotation, and the most neutral valgus/varus rotation compared with unbalanced knees.ConclusionThese findings indicate the importance of adequate intraoperative joint gaps in deep flexion and ML soft tissue balance throughout the range of motion.Level of evidenceLevel II.