Although human gait has been studied for more than one hundred years, it was not until the late 1970s that new developments in computer technology and optoelectric devices allowed researchers to upgrade the gait data collection and processing from two-dimensional or pseudo 3-D to truly 3-D. However, despite being anticipated to help clinical decision making, gait analysis has generally failed to provide information critical to make decisions about the individual patient due to a variety of reasons.

The goal of this study was to develop an integrated gait analysis system (Questor Gait Analysis In Three-dimensions (QGAIT}) which requires a motion tracking system augmented with force plate, standardized X-ray and EMG information to evaluate individual loading patterns at the knee. It was achieved by two separate, but closely related knee models. The first one was the shank model, which applied the "inverse dynamics approach" to calculate the net joint reaction forces and moments at the knee joint. The second one, the muscle model, simplified anatomical structures of the knee and used EMG information to estimate the forces produced by major muscle groups crossing the knee joint. Integrating the results from the shank model, the muscle model was able to provide information on bone-on-bone forces, tibial plateau forces at the proximal end of the tibia, and patellofemoral joint forces. Recent technological development in motion tracking systems and standardized X-ray procedure allowed the first model to be more sophisticated than most previous models, and permited a thorough sensitivity analysis on the accuracy and reliability of the data. The second model was explorative in nature. It should be treated as a basic model on which more complicated models can be built with the ever-improving biomedical techniques.

The QGAIT system was applied to 35 subjects selected from young, normal population (Ages between 20 and 30). Means and standard deviations were calculated for kinematic and kinetic curves during one complete gait cycle. They can be used as baseline data to compare with other normal and pathological subject groups in the future.