The objective of this study is to evaluate the surgical outcome of anterior displacement of the tibial tuberosity,(Maquet procedure)for reducing Patellofemoral joint contact force The in vivo experimental knee joint geometric data with a biomechanical model were used to simulate the Maquet procedure.Six healthy young adults performed weight-bearing knee flexion-extension by ascending a one-step stair.Dynamic X-ray images of the knee were continuously recorded by a video-fluoroscopic system.These X-ray images were analyzed on a computerized digitizing system to get the knee joint geometric data.Based on the continuous in vivo geometric data,computer surgery simulation was studied on 6 right knees with advancement of 3,5,10,15,and 20 degrees of tlie patellar tendon insertion.Evaluation of the simulation consequences from a biomechanical view point showed that the Maquet procedure reduced the patellofemoral joint reaction force only up to 207% at 90 degrees of knee flexion angle.The patel lofemoral joint reaction force had 50% reduction only when the knee flexion angle was less than 20degrees, and only when patellar tendon was moved outwards by 15 or 20 degrees.This represented nearly one inch of the anterior displacement of the tibial tuberosity.The results also showed that the Maquet procedure would decrease up to 20% of the force transmission effciency of the patellofemoral mechanism,which would cause the mechanical consequences of the operation to be only minor at knee flexion angles greater than 20 degrees.These findings suggest that the Maquet procedure is only favorable to elderly or less active patients assuming small knee flexion angle activities.