Fig 1.
Functional principle of the HiL simulation for testing THR with respect to dislocation.
The transfer between the musculoskeletal model and the physical setup is illustrated within the two control loops on kinematic and force level, respectively. The THR components are attached to mounting devices which are fixed to the endeffector of the robot (stem) and the compliant support (cup).
Fig 2.
Physical setup of the HiL test system for testing THR.
The THR components are fixed on mounting devices attached to the endeffector and the compliant support, respectively. Measurements are taken via the force-torque sensor and displacement sensors.
Fig 3.
Multibody system of the lower extremity for testing THR.
(a) Multibody topology with illustration of the joint coordinates and the fictive planar joint in the sagittal plane indicated as one revolute (R) and two prismatic (P) joints. (b) Measured and transferred coordinates ,
,
in constrained directions of the THR. (c) Musculoskeletal model with implanted CAD geometries of the THR.
Table 1.
Configurations for nine HiL simulations with varying model and test parameters.
Fig 4.
Predicted hip joint reaction force fr for the normal maneuver compared to in vivo measurements of three male patients (HSR, KWR and PFL) [33].
All force components are given with respect to the global reference frame [66], shifted and rearranged with respect to the maxima of the corresponding resultant used as reference point [67], and mirrored to the left hip joint [33]. a Sitting down. b Standing up.
Table 2.
Relative deviations estimated at peak values between predictions of the HiL test system and hip contact forces derived from three instrumented patients [33] for normal sitting down and standing up.
Fig 5.
Impact of friction under dry and lubricated conditions on HiL-simulated THR load situation for a deep seating-to-rising motion cycle.
The HiL simulations are based on parameter sets ②, ③ from Table 1. a Absolute value of predicted reaction force |fr|. b Absolute value of measured resisting torque |τf|.
Fig 6.
Impact of implant position on HiL-simulated THR load situation for a deep seating-to-rising motion cycle.
Implant positions are defined by inclination ι, cup anteversion β, and stem antetorsion ϑ with parameter sets ③, ④, ⑤, ⑥ from Table 1. Impingement occurs at ○ and dislocation at ◇. a Flexion angle q3. b Measured displacement |c| between femoral head and acetabular cup. c Predicted reaction force |fr|. d Measured resisting torque |τf|.
Fig 7.
Impact of load level adjusted by body mass on HiL-simulated THR load situation for deep seating-to-rising.
The HiL simulations are based on parameter sets ②, ③, ④ from Table 1. Impingement occurs at ○ and dislocation at ◇. a Predicted reaction force |fr| over flexion angle. b Measured resisting torque |τf| over flexion angle.
Fig 8.
Impact of muscle element removal emulating a posterior surgical approach on HiL-simulated THR load situation with focus on the sitting down phase of the deep maneuver.
The HiL simulations are based on parameter sets ②, ③ from Table 1. a Comparison between the intact (blue lines) and the resected (red lines) case for hip joint rotations q3, q1, q2, measured displacement |c| between femoral head and acetabular cup, components of the predicted reaction force fr given in the pelvic reference frame [49], and measured resisting torque |τf|. Impingement occurs at ○ and dislocation at ◇. b Direction of the hip joint reaction force with respect to the frontal plane of the pelvic reference frame [49] with illustration of the head position at and after impingement for the intact (above) and the resected (below) case.