At present, wear investigations of total hip replacement (THR) are performed in accordance with the ISO standard 14242, which is based on empirically determined relative motion data and exclusively describes the gait cycle. However, besides continuous walking, a number of additional activities characterize the movement sequences in everyday life and influence the wear rates as well as the size and shape of wear debris. Disagreements of in vitro and in vivo wear mechanisms seemed to be a result of differences between in vitro and in vivo kinematics and dynamics. This requires an optimization of the current test procedures and parameters. Hence, the aim of the present study was to evaluate most frequent activities of daily living, based on available in vivo data, in order to generate parameter sets according to loading and rotational movements close to the physiological situation.For the generation of angular patterns, time-dependent three-dimensional trajectories of reference points were used from the HIP9...

IntroductionDislocation of total hip replacements (THRs) remains a severe complication after total hip arthroplasty. However, the contribution of influencing factors, such as implant positioning an...

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.

Tripolar systems have been implanted to reduce the risk of recurrent dislocation. However, there is little known about the dynamic behavior of tripolar hip endoprostheses under daily life conditions and achieved joint stability. Hence, the objective of this biomechanical study was to examine the in vivo dynamics and dislocation behavior of two types of tripolar systems compared to a standard total hip replacement (THR) with the same outer head diameter. Several load cases of daily life activities were applied to an eccentric and a concentric tripolar system by an industrial robot. During testing, the motion of the intermediate component was measured using a stereo camera system. Additionally, their behavior under different dislocation scenarios was investigated in comparison to a standard THR. For the eccentric tripolar system, the intermediate component demonstrated the shifting into moderate valgus-positions, regardless of the type of movement. This implant showed the highest resisting torque against dislocation in combination with a large range of motion. In contrast, the concentric tripolar system tended to remain in varus-positions and was primarily moved after stem contact. According to the results, eccentric tripolar systems can work well under in vivo conditions and increase hip joint stability in comparison to standard THRs.

At present, wear investigations of total hip replacements are performed in accordance with the ISO standard 14242, which is based on simplified kinematic and force data of the gait cycle. The aim of this analytical study was to generate parameter sets of daily life activities in order to replicate more realistic joint load situations in wear testing. Hence, published in vivo motion and force data of daily life activities were evaluated and adjusted using analytical techniques. The created kinematically and dynamically consistent parameter sets comprised time trajectories of three Cardan angles to describe the motion of the femur with respect to the pelvis and time trajectories of three force components, representing the hip joint contact force. The parameter sets include the activities of walking, knee bending, stair climbing and a combined load case of sitting down and standing up. Additionally, a motion sequence following the frequency of daily life activities was presented. Differences of the evaluated angular motions and joint contact forces in comparison to the ISO standard 14242-1 were pointed out. The results of this study offer the possibility to extend the kinematics and dynamics of the ISO standard test protocol and to support the loading conditions of hip wear simulators with a comprehensive set of motions and loads close to reality.

To speed up the degradation of corn stover directly returned to soil at low temperature, the corn stover-degrading microbial consortium GF-20, acclimated to biological decomposition in the frigid region, was successfully constructed under a long-term limiting substrate. To evaluate its potential in accelerating the decomposition of un-pretreated corn stover, the decomposing property, fermentation dynamic and the microbial diversity were analyzed. GF-20 degraded corn stover by 32% after 15-day fermentation at 10°C. Peak activities of filter paperlyase (FPA), β-glucosidases (CB), endoglucanases (Cx), and cellobiohydrolases (C1) were 1.15, 1.67, 1.73, and 1.42 U mL−1, appearing at the 6th, 3rd, 11th, and 9th d, respectively. The pH averaged at 6.73–8.42, and the optical density (OD) value peaked at 1.87 at the 120 h of the degradation process. Cellulase, hemicellulase and lignin in corn stover were persistently degraded by 44.85, 43.85 and 25.29% at the end of incubation. Result of denaturing gradient gel electrophoresis (DGGE) profiles demonstrated that GF-20 had a stable component structure under switching the temperature and pH. The composition of the GF-20 was also analyzed by constructing bacterial 16S rDNA clone library and fungal 18SrDNA-PCR-DGGE. Twenty-two bacterial clones and four fungal bands were detected and identified dominant bacteria represented by Cellvibrio mixtus subsp., Azospira oryzae, Arcobacter defluyii, and Clostridium populeti and the fungi were mainly identified as related to Trichosporon sp.

Instability of total knee replacements (TKRs) remains one of the most prevalent complications after total knee arthroplasty. Especially the actual event of instability involving complex interactions between implant components and soft tissue structures is not well understood. Therefore, the purpose of this work is to introduce a novel approach for testing TKRs with respect to stability of the artificial knee joint based on a mechatronic hardware-in-the-loop (HiL) test system. The mechanical test setup is composed of an industrial robot with a compliant support for the endoprosthesis to be tested. It interacts with a biomechanical multibody model consisting of all relevant body parts of the lower extremity incorporating ligament structures of the knee joint. According to the movement angles and reaction forces/torque provided by the multibody model, the robot rotates and loads the femoral component with respect to the tibial component. The resulting position and loading of the femoral component are measured and fed back into the model, thus closing the control loop for HiL simulations. The functional principle of the HiL simulation is proven by simulating a passive flexion movement of a bicondylar, posterior cruciate ligament retaining TKR using the described biomechanical multibody model.

ClInICAl BACKGrounD One of the most prevalent reasons for total joint revision is instability of the artificial joint (see Fig. 1). With regard to hip endoprostheses, dislocation of the prosthetic head represents a major reason for revision surgery. Mechanisms linked to the dislocation process involve prior prosthetic or bony contact (impingement), and spontaneous separation due to dynamic forces. Similarly, instabilities and adverse kinematics in knee endoprostheses constitute one of the most important reasons for implant failure. As knee endoprostheses are, by design, less constrained than hip endoprostheses, instability mechanisms are caused by excessive relative movement between the joint partners resulting in damage of surrounding soft tissue and hence an unstable joint articulation. Numerous clinical and biomechanical studies address the issue of instability pointing out several influencing factors. Soft tissue condition, implant design and positioning have each been frequently referred to as major factors. However, the process leading to an unstable artificial joint and the precise contribution of each influencing factor is not yet fully understood as in vivo measurements of instabilityassociated maneuvers are discouraged by ethical and technical reasons. Therefore, we follow a novel strategy to test total hip and knee endoprostheses in instability scenarios under reproducible, physiological boundary conditions. The approach consists of a Hardware-in-theLoop (HiL) simulation where the anatomic environment of the artificial joint is completely extracted into a musculoskeletal multi-body model generated in SIMPACK. The interaction with Instabilities of artificial joints are prevalent complications in total joint arthroplasty. Due to the variety of influencing factors involving complex interactions between implant components and soft tissue structures, the actual process leading to artificial joint instability and adverse kinematics is not fully understood. As ethical and technical reasons discourage in vivo measurements, our research group follows a novel approach in the field of orthopaedic biomechanics to test instability scenarios of hip and knee endoprostheses under physiological boundary conditions. the approach consists of a Hardware-in-the-loop (Hil) simulation where a musculoskeletal multi-body model interacts with an industrial robot. SIMPACK is used to generate the musculoskeletal multi-body model and to provide a realtime-capable standalone model for implementation into the Hil simulation. Musculoskeletal Multi-Body Modeling used for Hardware-in-the-loop Simulations

Instability of artificial joints is still one of the most prevalent reasons for revision surgery caused by various influencing factors. In order to investigate instability mechanisms such as dislocation under reproducible, physiologically realistic boundary conditions, a novel test approach is introduced by means of a hardware-in-the-loop (HiL) simulation involving a highly flexible mechatronic test system. In this work, the underlying concept and implementation of all required units is presented enabling comparable investigations of different total hip and knee replacements, respectively. The HiL joint simulator consists of two units: a physical setup composed of a six-axes industrial robot and a numerical multibody model running in real-time. Within the multibody model, the anatomical environment of the considered joint is represented such that the soft tissue response is accounted for during an instability event. Hence, the robot loads and moves the real implant components according to the information provided by the multibody model while transferring back the position and resisting moment recorded. Functionality of the simulator is proved by testing the underlying control principles, and verified by reproducing the dislocation process of a standard total hip replacement. HiL simulations provide a new biomechanical testing tool for analyzing different joint replacement systems with respect to their instability behavior under realistic movements and physiological load conditions.