A New System for Soft-Tissue Balance Measurement in Total Knee Replacement

In this paper, new soft-tissue balance measurement method and system are proposed to meet the quantitative requirement of soft-tissue balance measurement in total knee replacement (TKR). In our system, six precise force sensors are embedded in the front-end measurement device (FEMD), which is inserted into the knee joint. Each pressure of the sensor is responsive to a force generated between the condyle and the device and represents the force of soft tissues in the posterior, middle, and anterior positions of the medial/lateral portion of the knee joint, respectively. The force corresponding to its distribution is displayed in a 2-D or 3-D manner in real time with an accuracy of better than 0.098 N. Furthermore, the FEMD has the function of changing the gap distance between its upper and lower plates by a double-screw structure to adjust the space of the knee joint in the range from 20.0 to 31.0 mm. Finally, the system was used in the soft-tissue release of medial collateral ligament (MCL) in five cadavers and quantitatively measured the force change in the extension gap or flexion gap after three kinds of MCL release during TKR. The results showed that the measurement system could accomplish the force measurement and the distance adjustment of the knee joint.