Hardware-in-the-Loop Simulation for Dynamic Analysis of the Shoulder after Total Joint Replacement

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In recent years the artificial replacement of shoulder joints has been established as standardised treatment with rising numbers. Highly varying complication rates along with functional failures, however, prove that many problems remain unresolved after total shoulder arthroplasty. In this regard, a profound understanding of underlying failure mechanisms leading to instability, dislocation, muscle dysfunction or joint stiffness does not exist. Especially this applies for the identification and quantification of potential influencing factors. For this biomechanical investigations would be required which provide insights into the course of events under in-vivo conditions during complications and failures. Due to inherent shortcomings this demand cannot be met by current testing or simulation techniques. Furthermore, measurements on instrumented patients are strongly limited for ethical reasons.The objective of this project is to conduct in-depth analyses of the complex joint dynamics after total shoulder arthroplasty under in-vivo-like conditions based on a hardware-in-the-loop (HiL) approach. Hereby a musculoskeletal multibody model and an industrial robot that moves and loads the implant components are in mutual interaction. Into the multibody model all relevant muscle structures that are responsible for physiological hand and arm movements are implemented. A major priority is the prediction of muscle and joint forces in the HiL environment which is addressed by using inverse dynamics techniques. To establish the HiL test system further advancements within the HiL environment that was previously developed for testing total hip and knee replacements are required along with modifications of the physical setup. A key aspect is the validation of the overall HiL test system against experimental data derived from patients with instrumented shoulder implant. Our project focuses on the systematic assessment of potential chain of effects for physiological movements and loads which are connected to functional deficiencies, joint instability, and implant failure. First studies will be conducted with respect to effects of different muscular dysfunctions on the glenohumeral joint addressing open clinical questions. In addition, kinematic redundancies in the model topology are transcribed into alternative joint trajectories by means of an active path planning algorithm. This way reproducible and physiological arm movements affected by complications can be replicated. As a result physiological movements and loads of the shoulder after total joint replacement will be simulated for the first time under consideration of the real contact conditions and all relevant muscular structures of the shoulder girdle and upper extremity.