Hip joint contact forces during stumbling

Aim. To determine whether load directions for stumbling are similar to those for common activities and whether stumbling can be realistically simulated under laboratory conditions without endangering the patients. Method. The magnitudes and directions of hip contact forces were measured during real and simulated stumbling and compared with those found during various other everyday activities. Measurements were obtained by use of hip implants with built-in load sensors and telemetry. Results. Peak forces are approximately twice as high during real stumbling as during any other activity and may range higher than eight-times the body weight. Simulated stumbling leads to much lower contact forces, especially if this happens after a warning. Accidental stumbling in everyday situations should, therefore, be avoided, especially in patients with hip replacements or arthrosis. Conclusions. The directions of peak hip contact forces relative to the femoral bone are nearly constant for any activity, including real stumbling. This observation supports the assumption that muscle and bone anatomy plus muscle function are optimized in order to minimize stresses in bone and muscles. Any impairment of such a mechanically balanced system will increase the musculoskeletal loads. Malposition of total hip implants or muscle deficits caused by the surgical approach must, therefore, be avoided or minimized.