[Predicting load bearing of the hip joint. Computerized analysis with a 3-D multibody model of the human]

Multibody analysis was applied to construct an advanced model of the human body, where the large joints and complete mass and inertial properties were implemented. The model represents the 50th-percentile rank of a male adult. The hip joint is controlled by three muscle forces. The muscle coordinates were taken from a data source, previously collected by our group. The model enables one to analyze 3D hip joint forces with respect to various joint angles and represents conceptually an improvement of the classical method of graphical statics, which was established by Pauwels [15]. A hip joint load of three times body weight was found in the single leg stance. A load of 3.7 times body weight was calculated when simulating a knee flexion angle of 90 degrees, and a ventral inclination of the resultant hip joint force was seen. A constant amount of gluteus medius muscle force was observed during flexion. An increasing flecting moment at the hip joint, however, had to be balanced by a significantly increased gluteus maximus muscle force. As a consequence, torsional forces can be studied by the system presented here and should also be considered when testing stems of hip prostheses. External muscle and joint forces are provided and can be used as input data for stress analyses.