A development of tension and length measurement system for knee bending motion in medial patello-femoral ligament reconstruction

Medial patello-femoral ligament (MPFL) reconstruction surgery requires tension and length information of the graft for proper function. Current technique fixes the graft with subjective feeling of the tension and length. Therefore, the technique has not been established well due to lack of quantitative information. To measure the tension and length change at the same time, we manufactured a tension and length measurement system with a tension sensor and a rotary encoder. In the experiment, we calibrated an experiment of the tension sensor with the stress testing machine. We measured force change when the tension sensor was pulled in the horizontal direction by using the load cell tension sensor in the calibration experiments. In the tension measurement experiment, we measured the changes in tension and length of the suture which was attached to the position of MPFL during flexion and extension by using imitation femur and patella. The change of the length of the suture was measured with a rotary encoder. Consequently, the proposed system could measure tension and length information of MPFL simultaneously.