The objective of this study was to develop a method to estimate thigh-calf contact force during heel-rise squatting posture, which is important for analyzing the kinetics of the lower limb during deep knee flexion; however, the measured forces varied widely among test subjects. We also considered joint angles, rather than only individual anthropometric, such as height, body weight (BW), or body mass index (BMI). We created estimation equations by a linear combination of both physical and posture parameters, and then performed the measurement experiment with 10 healthy males. Test subjects were asked to take a squatting posture, and to bend their upper bodies forward and backward. We measured thigh-calf contact force by placing a pressure distribution sensor sheet between the thigh and calf. At the same time, the joint angles were measured as estimation parameters. Coefficients of the estimating equations were determined to minimize the root mean square error of the estimated and measured values. We compared four estimation equations, using physical and posture parameters, as well as those selected from all parameters, which are easily measurable. As a result, the estimation accuracy improved by using both physical and posture parameters. The average magnitude of the thigh-calf contact force was 0.92±0.24BW, and the average error of estimation was 0.06BW. The error was 0.11BW by using only physical parameters, and was 0.15BW by using only posture parameters. Despite this, even the estimation error using selected parameters was 0.07BW, while the maximum error was 0.25BW. We confirmed that there was little posture change adversely affecting thigh-calf contact force. Individual anthropometric parameters were important for estimation, although we used similar subjects for gender, age, and physical size. In the future, we will be recruiting more test subjects and discussing the effect of physical parameters, not only anthropometric values.

The objective of this study was to find out the effect of tibial position and orientation to patellofemoral kinetics, especially during deep knee flexion. The data about patellofemoral kinetics is necessary for calculating tibiofemoral joint force which is used to evaluate a design of knee prosthesis, however, there have been no data how it changes by tibial anterior translation or internal rotation which recent prostheses are aiming. We performed a three-dimensional model analysis with axioms of point contact and force equilibrium. The flexion angle was from 0° to 150° by four conditions. The neutral condition was based on the two-dimensional analysis using PS type of the prosthesis, without internal rotation and plenty femoral roll back. The other conditions were with over 20mm of tibial anterior translation, with 15° of tibial internal rotation, and both the translation and rotation during deep knee flexion. As a result, patellofemoral joint force reduced by tibial anterior translation and did not change by tibial rotation. Tensile force of patella tendon did not change by the tibial position/orientation. By rotating tibia internally, medial contact force increased and lateral reduced. Moreover, tibial anterior translation facilitated the dislocation of patellofemoral joint, and lateral side lifted off with tibial internal rotation. The contact force reduced rapidly before the lift off, and medial contact force increased by the lateral lift off. In this case, although the magnitude of the patella tendon force did not change, the direction of the force might change unignorably. Both tibial anterior translation and internal rotation might be necessary to be capable of deep knee flexion, however, it is also necessary to discuss the interaction between tibiofemoral and patellofemoral joints for evaluating the new prosthesis intending deep knee flexion.

No abstract