| Description |
During flexion and extension of the human knee, the angle between the long axis of the femur and the quadriceps tendon varies approximately 30°. Due to its magnitude, it would seem important to account for this variation in order to effectively represent in vivo circumstances in a model. However, if the changing angle is not important in effectively reflecting in vivo circumstances in a model, it would greatly simplify models by allowing a single quadriceps tendon to femoral axis angle to be selected and held constant in the model. The purpose of this study was to determine whether the quadriceps tendon to femoral axis angle is important in constructing a physiological model of the human knee joint. A model was constructed that allowed for cyclical flexion and extension of the knee. It was possible to control the quadriceps to femoral axis angle and hold it constant during different cycles of testing. By looking at the forces developed in the quadriceps tendon during flexion and extension, it was possible to determine whether or not the quadriceps tendon to femoral axis angle is important in designing a model. This was based on the differences seen in quadriceps tendon loads for a particular angle of flexion/extension with varying quadriceps tendon to femoral axis angles (Q:F angles). The model ran through cycles of extension and flexion, and quadriceps tendon 11 loads were tracked and marked at 30°,45°,60°,75°, and 90° of flexion/extension for tests where the Q:F angle varied from -10° to + 10°. Significant differences in loads for a single flexion/extension angle with varying Q:F angles demonstrated that it is important to account for the changing angle in models mimicking flexion/extension of the knee. During testing, minimum variation occurred at 30° extension, where quadriceps tendon loads changed from 22.9 kg where the Q:F angle was -10° to 25.3 kg where the angle was +5°. Maximum variation occurred at 60° extension, where loads ranged from 74.9 kg to 79.7 kg. Variation in mean quadriceps tendon loads for a given angle of flexion/extension therefore ranged from 2.4 kg to 4.8 kg. Subsequently, it is not possible to assume that a model will adequately reflect in vivo circumstances if a single Q:F angle is chosen and held constant during use of that model, and the physiological change in the Q:F angle during activity at the knee should be accounted for in models attempting to physiologically mirror in vivo circumstances. 111 |
