A new paradigm for the in vitro simulation of sideways fall loading of the proximal human femur

Although the direction of loads applied to the proximal human femur is unpredictable during sideways fall, most in itro and numerical simulations refer to a single loading condition (15° internal rotation; 10° adduction), which has been anecdotally suggested in the 1950s. The aim of the present study was to improe in itro simulations of sideways falls on the proximal femur. An in itro setup was deeloped that allowed exploring a range of loading directions +/-90° internal-external rotation; 0°-50° adduction). To enable accurate control of the loading conditions (direction and magnitude of all load components applied to the femur), the setup included a number of low-friction linear and rotary bearings. The setup was instrumented with an axial and a torsional load cell, three displacement transducers and a rotation transducer to monitor the most significant components of load/displacement during testing. The strain distribution was measured on the bone surface (16 triaxial strain gauges, 2,000 Hz). Fracture was recorded with a high-speed camera. The setup was successfully tested on a cadaeric femur non-destructiely (12 loading configurations) and destructiely (15° internal rotation; 10° adduction). All measurements were highly repeatable (the displacements of the femoral head aried by <2% between repetitions; the tilt in the frontal plane by <0.05°; and strain aried on aerage 0.34% between repetitions). The displacement of the femoral head aried by oer 50% when the same force was applied in different directions. Principal strains at the same location aried by oer 70%, depending on the direction of the applied force. The high-speed ideo enabled the identification of the point of fracture initiation. This study has shown that a new paradigm for testing the proximal femur (including improed testing conditions and a ariety of loading configurations) can proide more accurate and more extensie information about the state of strain.