Limits...
A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions.

Herrmann S, Kluess D, Kaehler M, Grawe R, Rachholz R, Souffrant R, Zierath J, Bader R, Woernle C - PLoS ONE (2015)

Bottom Line: The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces.Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads.Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedics, University Medicine Rostock, Rostock, Germany.

ABSTRACT
Constant high rates of dislocation-related complications of total hip replacements (THRs) show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL) simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

Show MeSH

Related in: MedlinePlus

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).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4696831&req=5

pone.0145798.g001: 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).

Mentions: For the spatial load case (Fig 1), the free directions are specified as the rotations of the femur with respect to the pelvis with the angles q1 (adduction/abduction), q2 (internal/external rotation) and q3 (flexion/extension). At a current time instant t, the musculoskeletal model delivers values of the angles q1, q2 and q3 which are transferred to the robot controller. Accordingly, the femoral component of the THR is rotated in the position with angles , and by the robot under position control. The transferred values denoted by bars normally differ from the original values without bars due to signal delays and the limited dynamic bandwidth of the controlled robot. Resisting torque components , , usually due to friction, are measured along the coordinates , and as a consequence of the movement, and fed back to the model closing the first control loop of the HiL simulation.


A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions.

Herrmann S, Kluess D, Kaehler M, Grawe R, Rachholz R, Souffrant R, Zierath J, Bader R, Woernle C - PLoS ONE (2015)

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).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696831&req=5

pone.0145798.g001: 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).
Mentions: For the spatial load case (Fig 1), the free directions are specified as the rotations of the femur with respect to the pelvis with the angles q1 (adduction/abduction), q2 (internal/external rotation) and q3 (flexion/extension). At a current time instant t, the musculoskeletal model delivers values of the angles q1, q2 and q3 which are transferred to the robot controller. Accordingly, the femoral component of the THR is rotated in the position with angles , and by the robot under position control. The transferred values denoted by bars normally differ from the original values without bars due to signal delays and the limited dynamic bandwidth of the controlled robot. Resisting torque components , , usually due to friction, are measured along the coordinates , and as a consequence of the movement, and fed back to the model closing the first control loop of the HiL simulation.

Bottom Line: The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces.Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads.Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedics, University Medicine Rostock, Rostock, Germany.

ABSTRACT
Constant high rates of dislocation-related complications of total hip replacements (THRs) show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL) simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

Show MeSH
Related in: MedlinePlus