Elektrodynamische Prüfmaschine
Zusammenfassung der Projektergebnisse
For our applications in orthopaedics and biomechanics, the testing system has allowed for tests to be conducted in axial configuration, using static and dynamic rates. This is necessary to characterize the fixation stability of implanted medical devices. The system was also used to mechanically test the outcomes of biomaterials such as bone cements used in our vertebroplasty projects, by performing tests in dynamic cyclic conditions simulating daily activities at the spine. Our workgroup has developed testing methodologies to evaluate the fixation of shoulder prosthetic components implanted in cadaveric scapulae. For this, it was critical to use a testing system that allowed static loading of the shoulder joint at moderate loads of 600N, while cyclically moving the components in anatomical directions. In a recent study, we were able to confirm some previous hypotheses on the role of periprosthetic bone density on the loosening of anatomical glenoid components at the shoulder, which is known to be the most common complication after total shoulder arthroplasty. Our results suggest that fixation failure will most likely occur in bone of lower density, and that fixation design itself may play a secondary role. One area of our current research of fracture stabilization, done in partnership with traumatology colleagues, allowed us to further use the combined dynamic and static testing capabilities of the system. T-type acetabular fractures were in simulated for one of our projects that investigated the potential favorability of minimally invasive treatment options over the already established open anterior locking plate osteosynthesis. The testing system was then used to mechanically load these constructs for characterizing fixation stability as well as post-surgical stiffness under moderate cyclic loads. Specimens could be loaded cyclically between moderate loads of 200 and 600N, and results demonstrated that minimally invasive fixation techniques for T-type acetabular fractures offer promising biomechanical stability in non- or slightly displaced fractures. The device was furthermore extensively used for evaluating the fixation stability of femoral stems in a series of experimental studies conducted by our work group. Typically, these tests are done with femoral stems implanted in synthetic bones while repeated loads are applied that simulate physiological conditions of relevant daily activities. This was done using the specific dynamic capabilities of the device, which allowed us to cyclically load the implant-bone constructs under loads between 300 and 1700kN at 1 Hz, while monitoring relative displacements or micromotions between the implants and the bone. Consequently, our studies were useful in demonstrating some critical factors affecting fixation stability of femoral stems. Using our established protocols allowed us to evaluate how varus position of cementless stems, a common malalignment in total hip arthroplasty associated with clinical incidence of increased risks of thigh pain, can alter bone strain distributions. By testing stems in dynamic loading tests while strains on the bone surfaces were measured using strain gages, we were able to confirm clinical observations with increased strains distributions in the case of varus malalignments, as well as increased micromotions. Our group could also show that undersizing of cementless hip stems, believed to be a risk factor for aseptic loosening and early subsidence, can indeed affect their fixation stability. Additional findings by our group pertaining to the use of this testing system for femoral stem stability aimed at evaluating if metaphyseal anchored Metha short stem can safely be revised with a standard CLS stem. Tests showed that SHA (Metha) and standard THA (CLS) provide a good primary stability, however with different pattern of anchorage. Finally, using similar testing protocols, our group could show that specimen size for such tests seems to be a minor influence factor for biomechanical evaluation of cementless stems, as they provided similar fixation stabilities. Future tests of femoral stem fixation are in planning that will include torsional loads, and was one of the requirements for this test system. In all these projects, the system was operated by students with medical or engineering backgrounds, after proper training by our research personnel. This is also because the testing device does not need sophisticated prior adjustments and maintenance typical of hydraulic systems. So far our testing system worked flawlessly. The self-explanatory aspect of the software tools allowed easy learning for students to conduct experimental-based research projects, which was critical for us as an academic training facility. This was clearly evidenced by increased autonomy when performing the tests, in comparison with our former, larger equipment which required presence of staff at all time. It was also perfectly matched for our testing protocols where loads and displacement had to be controlled at a variety of rates and magnitudes representative of physiological conditions, which was not possible using the former system where the dynamic capabilities far exceeded the physiological requirements.
Projektbezogene Publikationen (Auswahl)
- Can the metaphyseal anchored Metha short stem safely be revised with a standard CLS stem? A biomechanical analysis. Int Orthop. 2017 Dec;41(12):2471-2477
Yan SG, Woiczinski M, Schmidutz TF, Weber P, Paulus AC, Steinbrück A, Jansson V, Schmidutz F
(Siehe online unter https://doi.org/10.1007/s00264-017-3497-z) - Influence of different sizes of composite femora on the biomechanical behavior of cementless hip prosthesis. Clin Biomech (Bristol, Avon). 2017 Jan;41:60-65
Schmidutz F, Woiczinski M, Kistler M, Schröder C, Jansson V, Fottner A
(Siehe online unter https://doi.org/10.1016/j.clinbiomech.2016.12.003) - Influence of undersized cementless hip stems on primary stability and strain distribution. Arch Orthop Trauma Surg. 2017 Oct;137(10):1435-1441
Fottner A, Woiczinski M, Kistler M, Schröder C, Schmidutz TF, Jansson V, Schmidutz F
(Siehe online unter https://doi.org/10.1007/s00402-017-2784-x) - Minimally invasive screw fixation is as stable as anterior plating in acetabular T-Type fractures - a biomechanical study. Orthop Traumatol Surg Res. 2018 Sep 1. pii: S1877-0568(18)30239-1
Becker CA, Kammerlander C, Cavalcanti Kußmaul A, Dotzauer F, Woiczinski M, Rubenbauer B, Sommer F, Linhart C, Weidert S, Zeckey C, Greiner A
(Siehe online unter https://doi.org/10.1016/j.otsr.2018.06.013) - Periprosthetic bone quality affects the fixation of anatomic glenoids in total shoulder arthroplasty: in vitro study. J Shoulder Elbow Surg. 2018 Sep 28. pii: S1058-2746(18)30539-1
Chamseddine M, Breden S, Pietschmann MF, Müller PE, Chevalier Y
(Siehe online unter https://doi.org/10.1016/j.jse.2018.07.012) - Varus malalignment of cementless hip stems provides sufficient primary stability but highly increases distal strain distribution. Clin Biomech (Bristol, Avon). 2018 Oct;58:14-20
Fottner A, Woiczinski M, Kistler M, Schröder C, Schmidutz TF, Jansson V, Schmidutz F
(Siehe online unter https://doi.org/10.1016/j.clinbiomech.2018.07.006)
