Abstract
Total knee arthroplasty can be performed with the balanced gap technique with the tibia cut first guided by the use of a tensor. In a case series of 54 cruciate retaining knee implants (Balansys) 150 N tension was applied to distract the extension gap and 100 N to distract the flexion gap.
The following conclusions could be drawn from the collected data:
The varus valgus laxity of the total knee joint measured with stress radiograms in extension was similar to that of the healty subjects with the same age and in flexion one degree more.
The anterior posterior laxity of the total knee joints compared to the healthy knees was on average 1 mm less.
The average ROM of the total knee joints was 118 degrees versus 130 degrees for the healthy knees
Ligament releases did not have a significant influence on the stability of the total knee joints.
The femur rotation guided by the ligament tension in flexion varied from −4 degrees to + 10 degrees referenced from the posterior condylar line. Only knees with a large medial ligament release had on average slighly less external rotation.
Patella position after surgery was not affected by this variable femoral component rotation, only preoperative maltracking was a predictor of postoperative maltracking.
One millimeter distraction of the flexiongap causes 1.9–2.3 mm anterior translation of the tibia indicating that very small gap changes in CR knee can cause a relative large shift of the contact point showing the difficulty to balance the PCL.
In conclusion the balanced gap technique with a tensor system results in very stable total knee implants with good range of motion. This tensor technique in cruciate retaining total knee arthroplasty is safe even when releases are performed. The variable femur rotation did not affect patella tracking.
