Marc Kraft

Human Achilles Tendon Plasticity in Response to Cyclic Strain: Effect of Rate and Duration

High strain magnitude and low strain frequency are important stimuli for tendon adaptation. Increasing the rate and duration of the applied strain may enhance the adaptive responses. Therefore, our purpose was to investigate the effect of strain rate and duration on Achilles tendon adaptation. The study included two experimental groups (N=14 and N=12) and a control group (N=13). The participants of the experimental groups exercised according to a reference protocol (14 weeks, four times a week), featuring a high strain magnitude (~6.5%) and a low strain frequency (0.17 Hz, 3 s loading/3 s relaxation) on one leg and with either a higher strain rate (one-legged jumps) or a longer strain duration (12 s loading) on the other leg. The strain magnitude and loading volume were similar in all protocols. Before and after the interventions, the tendon stiffness, Youngs modulus and cross-sectional area were examined using magnetic resonance imaging, ultrasound and dynamometry. The reference and long strain duration protocols induced significantly increased (P<0.05) tendon stiffness (57% and 25%), cross-sectional area (4.2% and 5.3%) and Youngs modulus (51% and 17%). The increases in tendon stiffness and Youngs modulus were higher in the reference protocol. Although region-specific tendon hypertrophy was also detected after the high strain rate training, there was only a tendency of increased stiffness (P=0.08) and cross-sectional area (P=0.09). The control group did not show any changes (P=0.86). The results provide evidence that a high strain magnitude, an appropriate strain duration and repetitive loading are essential components for an efficient adaptive stimulus for tendons.

Designs and performance of microprocessor-controlled knee joints.

Abstract In this comparative study, three transfemoral amputee subjects were fitted with four different microprocessor-controlled exoprosthetic knee joints (MPK): C-Leg, Orion, Plié2.0, and Rel-K. In a motion analysis laboratory, objective gait measures were acquired during level walking at different velocities. Subsequent technical analyses, which involved X-ray computed tomography, identified the functional mechanisms of each device and enabled corroboration of the performance in the gait laboratory by the engineering design of the MPK. Gait measures showed that the mean increase of the maximum knee flexion angle at different walking velocities was closest in value to the unaffected contralateral knee (6.2°/m/s) with C-Leg (3.5°/m/s; Rel-K 17.0°/m/s, Orion 18.3°/m/s, and Plié2.0 28.1°/m/s). Technical analyses corroborated that only with Plié2.0 the flexion resistances were not regulated by microprocessor control at different walking velocities. The muscular effort for the initiation of the swing phase, measured by the minimum hip moment, was found to be lowest with C-Leg (-82.1±14.1 Nm; Rel-K -83.59±17.8 Nm, Orion -88.0±16.3 Nm, and Plié2.0 -91.6±16.5 Nm). Reaching the extension stop at the end of swing phase was reliably executed with both Plié2.0 and C-Leg. Abrupt terminal stance phase extension observed with Plié2.0 and Rel-K could be attributed to the absence of microprocessor control of extension resistance.

Numerical evaluation and comparison of instantaneous anatomical knee joint axes and orthotic joint axes using MRI data under weight-bearing condition

This paper presents the numerical methods used for the calculation of the functional axes of the knee joint on different flexion angles with and without knee brace and the axes of the knee brace using MRI data. These methods were developed during a student research project in the framework of the research project “Evaluation of the possibilities of a functional assessment of orthopedic assistive technologies using open MRI” at the Institute of Medical Engineering at the Technical University of Berlin, which is about exemplarily working out methods for determining the congruence of the instantaneous anatomical knee joint axis and a knee orthosis joint axis.

Ein neues Verfahren zur patientenorientierten Zuordnung von Rollstuhlsitzkissen auf Basis von standardisierten Prüfverfahren / A novel method for patient-oriented assignment of wheelchair cushions based on standardized laboratory testing procedures

Abstract Rollstuhlsitzkissen sind die Schnittstelle zwischen Rollstuhl und Rollstuhlfahrer und übernehmen dabei Last übertragende und stabilisierende Aufgaben. Zusätzlich sollen sie helfen, Druckgeschwüre durch mechanische Entlastung und einen Abtransport von Feuchtigkeit und Wärme zu vermeiden. Die Auswahl eines Sitzkissen erfolgt dabei häufig anhand einer subjektiven Einschätzung der Sitzkisseneigenschaften, was die durchschnittliche Qualität der Versorgung negativ beeinflussen kann und unter Kostengesichtspunkten die Auswahl hochwirksamer Kissen nur schwer rechtfertigt. Dieser Artikel beschreibt ein Verfahren, Sitzkissen anhand von messtechnisch erfassten Kennwerten und einer standardisierten Patientenprofilerhebung auszuwählen. Dazu wird eine Übersicht über die am Markt erhältlichen Sitzkissen gegeben und Möglichkeiten erörtert, die Sitzkissen anhand von strukturierten Entscheidungshilfen nachvollziehbar auszuwählen und die Anforderungen des Patienten unterstützend einzuteilen und zuzuordnen. A wheelchair seat cushion represents the interface between the wheelchair and the wheelchair driver and has to manage the force transmission and the stabilization between both of them. An additional very important requirement is the prevention of pressure ulcers by pressure relief and the transfer of humidity and heat away from the patient. The allocation of a cushion to the patient happens normally on the base of a subjective description of the cushion without any transparent decision rules. Consequently the quality of this procedure could be improved by a better description of the cushion, based on standardized laboratory tests and by the development of decision tools helping to identify the main efforts of the user. This article describes a procedure that allows the allocation of wheelchair seat cushions based on the characteristic of cushions from standardized laboratory tests and on the brief description of the user. Additionally the existing principles for wheelchair cushions are listed, described and compared. The possibilities to develop structured decision tools for wheelchair cushions are discussed.

Reduction of thermal tissue damage caused by bipolar radiofrequency-induced thermofusion

Kröger M., Jaenicke A., Winter H., Nagel A., Buhr H.-J., Ritz J.-P., Lauster R.,Kraft M., Holmer C. Technical University of Berlin, Chair of Biomedical Engineering, Berlin, Germany Technical University of Berlin, Chair of Medical Biotechnology, Berlin, Germany 3 Charité – Universitätsmedizin Berlin, Department of General, Vascular and Thoracic Surgery 4 Helios Kliniken Schwerin, Department of General and Vascular Surgery

Prothesen und Orthesen

Prothesen und Orthesen werden in der Orthopadie und Unfallchirurgie, aber auch in vielen weiteren medizinischen Fachdisziplinen haufig verwendet. Wahrend Prothesen als kunstliche Ersatzstucke ganz unterschiedliche Korperteile ersetzen, sind Orthesen extern angewandte Hilfsmittel zur Veranderung der strukturellen und funktionellen Eigenschaften des neuromuskularen und des skelettalen Systems. Prothesen mussen in Endoprothesen, die innerhalb des Korpers angewandt werden, und in Exoprothesen unterschieden werden, die auserhalb des Korpers nutzbar sind. Orthesen gehoren in der Orthopadietechnik zu den sehr haufig genutzten Hilfsmitteln. Exemplarisch werden orthopadische und kardiovaskulare Endoprothesen (Gelenkimplantate, Herzklappenprothesen und kardiovaskulare Stents), Gliedmasenprothesen (Arm- und Beinprothesen) sowie Orthesen (Knieorthesen) vorgestellt.

Ausgewählte Beispiele wichtiger medizintechnischer Geräte

Medizinische Bildgebung ist die Kombination technischer und algorithmischer Verfahren zur Gewinnung orts‐ und evtl. zeitverteilter morphologischer oder physiologischer Grosen, deren Kenntnis der Erhaltung oder Wiederherstellung der Gesundheit dient.

Designs and performance of three new microprocessor-controlled knee joints

Abstract A crossover design study with a small group of subjects was used to evaluate the performance of three microprocessor-controlled exoprosthetic knee joints (MPKs): C-Leg 4, Plié 3 and Rheo Knee 3. Given that the mechanical designs and control algorithms of the joints determine the user outcome, the influence of these inherent differences on the functional characteristics was investigated in this study. The knee joints were evaluated during level-ground walking at different velocities in a motion analysis laboratory. Additionally, technical analyses using patents, technical documentations and X-ray computed tomography (CT) for each knee joint were performed. The technical analyses showed that only C-Leg 4 and Rheo Knee 3 allow microprocessor-controlled adaptation of the joint resistances for different gait velocities. Furthermore, Plié 3 is not able to provide stance extension damping. The biomechanical results showed that only if a knee joint adapts flexion and extension resistances by the microprocessor all known advantages of MPKs can become apparent. But not all users may benefit from the examined functions: e.g. a good accommodation to fast walking speeds or comfortable stance phase flexion. Hence, a detailed comparison of user demands and performance of the designated knee joint is mandatory to ensure a maximum in user outcome.

Bipolar radio-frequency-induced thermofusion of intestinal tissue – In vivo evaluation of a new fusion technique in an experimental study

Abstract Purpose: Bipolar radio-frequency-induced thermofusion (BiRTh) of intestinal tissue might replace conventional stapling devices which are associated with technical and functional complications. Previous results of our study group confirmed the feasibility to fuse intestinal tissue using BiRTh-induced thermofusion ex vivo. The aim of this study was now to evaluate the efficacy of fusing intestinal tissue in vivo by BiRTh-induced thermofusion. Materials and methods: In male Wistar rats a blind bowel originating from the caecum was closed either by BiRTh (n = 24) or conventional suture (n = 16). At 6 h, 48 h, 4 days, and 2 weeks after the procedure caecum bursting pressure was measured to compare both groups. Results: In total 18 of 21 (85.7%) thermofused and 15 of 16 (93.7%) sutured cecal stumps were primarily tight and leakage-proof (p > 0.05). The operative time was comparable in both groups without significant differences. Both groups showed increases in bursting pressure over the post-operative period. The mean bursting pressure for thermofusion was 47.8, 48.3, 55.2, and 68.0 mmHg, compared to 69.8, 51.5, 70.0 and 71.0 mmHg in the hand-sutured group (p > 0.05) after 6 h, 48 h, 4 days, and 2 weeks, respectively. Conclusion: These results suggest that BiRTh-induced thermofusion is a safe and feasible method for fusing intestinal tissue in this experimental in vivo model and could be an innovative approach for achieving gastrointestinal anastomoses.

Regelung eines Prüfstands für Beinprothesen

Zusammenfassung Zur Funktions- und Betriebsfestigkeitsprüfung moderner Beinprothesen für aktive amputierte Menschen wurde am Fachgebiet Medizintechnik der TU Berlin ein servohydraulischer Prüfstand entwickelt. Mithilfe einer robusten, adaptiven Regelungsstragie ist der Gangsimulator in der Lage, komplexe, hochdynamische Bewegungsabläufe mit Beinprothesen mit großer Genauigkeit durchzuführen.