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

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.

Dynamical analysis of dislocation‐associated factors in total hip replacements by hardware‐in‐the‐loop simulation

“…Relative displacements of the joint components were measured via the end‐effector's position sensor and the support's displacement sensors. Potentially occurring elastic deformations of the femoral stem were compensated by an error model in the control system …”

“…The numerical setup was given by a musculoskeletal multibody system (MBS) of the lower right extremity with the hip joint being replaced by the THR (Fig. a).…”

“…The insufficiency of gluteal and adjacent muscles was modeled by deactivating the respective force elements in the multibody model. Finally, two quadratic optimization algorithms were implemented to solve the mentioned redundancy problems.…”

“…In this manner, a comprehensive parameter study was implemented analyzing the impact of implant position (Table ), implant design (Table ) and muscle function (Table ), when performing deep sit‐to‐stand with femoral adduction (33 cm seat height), see Herrmann et al for explicit information on the motion maneuver.…”

“…Therefore, the purpose of the present study was to systematically analyze the impact of various instability‐related parameters, namely implant position and design as well as impaired muscle function, on THR stability while performing dynamic deep sit‐to‐stand with femoral adduction that is common in daily living activities. Within a validated hardware‐in‐the‐loop (HiL) setup, physical THR components actuated by a six‐axis industrial robot interact with an in situ‐like environment emulated by a musculoskeletal multibody model of the lower extremity. In this manner, the presented approach highlights the instability phenomena in the light of musculoskeletal dynamics and furthermore, allows for a reproducible analysis of the instability events under physiological‐like loading conditions.…”