HOW TO OBTAIN BALANCED FLEXION-EXTENSION GAPS

Abstract

Soft tissue balancing remains the most subjective and most artistic of current techniques in total knee arthroplasty. The flexion gap is traditionally measured at approximately 45 degree of hip flexion and 90 degree of knee flexion on the operation table. Despite of aiming equal joint gaps or tensions in flexion and extension, influence of the thigh weight on the flexion gap has not been documented. Therefore, the purpose of this study was to examine the flexion gaps in the 90–90 degree flexed position and the traditional 45–90 degree flexed position of hip-knee joints.

Thirty patients with osteoarthritic knee underwent total knee arthroplasty. After the PCL sacrifice, soft tissue releases, and bone cuts. Biomechanical properties of the soft tissue were obtained during the surgery, using the specially designed system. The system consists of two electric load cells in the tensioning device, digital output indicators, and an XY plotter. Load displacement curves were obtained in extension and in flexion. 160N was applied to open the joint gaps in the traditional 45–90 degree flexed position and the 90–90 degree flexed position of hip-knee joints. The flexion gap in the 90–90 degree flexed position of hip-knee joints was 2.1±1.2mm wider than that in the traditional 45–90 degree flexed position of hip-knee joints. The flexion gap had significant difference between the two different hip flexion angles (p< 0.001). Interestingly, the stiffness of curves obtained from the lateral in flexion is 1/3 lower than the other three.

In the traditional 45–90 degree flexed position of hip-knee joints on the operation table, the flexion gap is approximately 45 degree to the gravitation and influenced by the thigh weight. To avoid the influence of the thigh weight and obtain equal joint gaps or tensions in flexion and extension, the flexion gap should be checked in the 90–90 degree flexed position of hip-knee joints.

Extension and flexion gaps on the sagittal plane, and medial and lateral gaps on the coronal plane have to be well balanced. However, it is very difficult to match these four. It is still very questionable whether we can adjust these materials precisely and constantly or not.