Stiffness of soft tissue complex in total knee arthroplasty

The significance of achievement of soft tissue balancing in total knee arthroplasty is well recognized. There are few reports dealing with soft tissue tension in total knee arthroplasty. It is expected that the soft tissue tension will affect post-operative results such as postoperative ROM and stability. The purpose of this study was to evaluate tension properties of soft tissue complex of osteoarthritic knee in total knee arthroplasty. Sixty osteoarthritic knees that underwent primary total knee arthroplasty were investigated with a balancer and torque driver specially developed and adapted for this study. We gradually opened the extension and flexion space and measured the force to open it. We created a force-displacement curve in each case. Inclination of the curve indicated stiffness. We examined the stiffness average of all cases every 10 N. The stiffness was 8.9 and 8.5 N/mm (extension, flexion) in soft tissue tension of 60 N and 26.6 and 21.4 N/mm in 180 N. The stiffness became larger with an increase of soft tissue tension, and the stiffness of extension is significantly larger than that of flexion in each tension except for 60 N. Tension properties of soft tissue complex reveal that soft tissue can be easily extended in low soft tissue tension, and hardly extended in high tension.