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Background The onset and progression of osteoarthritis, but also the wear and loosening of the components of an artificial joint, are commonly associated with mechanical overloading of the structures. Knowledge of the mechanical forces acting at the joints, together with an understanding of the key factors that can alter them, are critical to develop effective treatments for restoring joint function. While static anatomy is usually the clinical focus, less is known about the impact of dynamic factors, such as individual muscle recruitment, on joint contact forces. Methods In this study, instrumented knee implants provided accurate in vivo tibio-femoral contact forces in a unique cohort of 9 patients, which were used as input for subject specific musculoskeletal models, to quantify the individual muscle forces during walking and stair negotiation. Results Even between patients with a very similar self-selected gait speed, the total tibio-femoral peak forces varied 1.7-fold, but had only weak correlation with static alignment (varus/valgus). In some patients, muscle co-contraction of quadriceps and gastrocnemii during walking added up to 1 bodyweight (~ 50%) to the peak tibio-femoral contact force during late stance. The greatest impact of co-contraction was observed in the late stance phase of stair ascent, with an increase of the peak tibio-femoral contact force by up to 1.7 bodyweight (66%). Conclusions Treatment of diseased and failed joints should therefore not only be restricted to anatomical reconstruction of static limb axes alignment. The dynamic activation of muscles, as a key modifier of lower limb biomechanics, should also be taken into account and thus also represents a promising target for restoring function, patient mobility, and preventing future joint failure. Trial registration German Clinical Trials Register: ID: DRKS00000606, date: 05.11.2010. Electronic supplementary material The online version of this article (10.1186/s12984-018-0434-3) contains supplementary material, which is available to authorized users.

During whole body vibrations, the total contact force in knee and hip joints consists of a static component plus the vibration-induced dynamic component. In two different cohorts, these forces were measured with instrumented joint implants at different vibration frequencies and amplitudes. For three standing positions on two platforms, the dynamic forces were compared to the static forces, and the total forces were related to the peak forces during walking. A biomechanical model served for estimating muscle force increases from contact force increases. The median static forces were 122% to 168% (knee), resp. 93% to 141% (hip), of the body weight. The same accelerations produced higher dynamic forces for alternating than for parallel foot movements. The dynamic forces individually differed much between 5.3% to 27.5% of the static forces in the same positions. On the Powerplate, they were even close to zero in some subjects. The total forces were always below 79% of the forces during walking. The dynamic forces did not rise proportionally to platform accelerations. During stance (Galileo, 25 Hz, 2 mm), the damping of dynamic forces was only 8% between foot and knee but 54% between knee and hip. The estimated rises in muscle forces due to the vibrations were in the same ranges as the contact force increases. These rises were much smaller than the vibration-induced EMG increases, reported for the same platform accelerations. These small muscle force increases, along with the observation that the peak contact and muscle forces during vibrations remained far below those during walking, indicate that dynamic muscle force amplitudes cannot be the reason for positive effects of whole body vibrations on muscles, bone remodelling or arthritic joints. Positive effects of vibrations must be caused by factors other than raised forces amplitudes.

Background and purpose - Registry-based studies have reported an increased risk of aseptic tibial loosening for the cemented Low Contact Stress (LCS) total knee replacement compared with other cemented designs; however, the reasons for this have not been established. We made a retrieval analysis with the aim of identifying the failure mechanism. Patients and methods - We collected implants, cement, tissue, blood, and radiographs from 32 failed LCS Complete cases. Damage to the tibial baseplate and insert was assessed. Exposure to wear products was quantified in 11 cases through analysis of periprosthetic tissue and blood. Implant alignment and bone cement thickness was compared with a control group of 43 non-revised cases. Results - Loosening of the tibial baseplate was the reason for revision in 25 retrievals, occurring at the implant-cement interface in 16 cases. Polishing was observed on the lower surface of the baseplate and correlated to the level of cobalt, chromium, and zirconium in the blood. No evidence of abnormally high polyethylene wear was present. For each 1 mm increase in cement thickness the odds of failure due to aseptic loosening decreased by 61%. Greater varus alignment was associated with a shorter time to failure. The roughness, Ra, of a new LCS baseplate's lower surface was 3.7 (SD 0.7) microm. Interpretation - Debonding of the tibial component at the implant-cement interface was the predominant cause of tibial aseptic loosening. A thin cement layer may partly explain the poor performance. Furthermore, the comparatively low tibial surface roughness and the lack of a keeled stem may have played a role in the failures observed. publishedVersion

Fragestellung: Um eine gleichmäßige Belastung im ersetzten Kniegelenk zu erreichen, werden die Komponenten beim Kniegelenkersatz an der mechanischen Beinachse ausgerichtet (Hutt, 2015). Allerdings führt dies zu einer Alteration der nativen Gelenklinie. Die kinematische Komponentenausrichtung[zum vollständigen Text gelangen Sie über die oben angegebene URL], Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2017)

Objective The external knee adduction moment (EAM) is often considered a surrogate measure of the distribution of loads across the tibiofemoral joint during walking. This study was undertaken to quantify the relationship between the EAM and directly measured medial tibiofemoral contact forces (Fmed) in a sample of subjects across a spectrum of activities. Methods The EAM for 9 patients who underwent total knee replacement was calculated using inverse dynamics analysis, while telemetric implants provided Fmed for multiple repetitions of 10 activities, including walking, stair negotiation, sit-to-stand activities, and squatting. The effects of the factors “subject” and “activity” on the relationships between Fmed and EAM were quantified using mixed-effects regression analyses in terms of the root mean square error (RMSE) and the slope of the regression. Results Across subjects and activities a good correlation between peak EAM and Fmed values was observed, with an overall R2 value of 0.88. However, the slope of the linear regressions varied between subjects by up to a factor of 2. At peak EAM and Fmed, the RMSE of the regression across all subjects was 35% body weight (%BW), while the maximum error was 127 %BW. Conclusion The relationship between EAM and Fmed is generally good but varies considerably across subjects and activities. These findings emphasize the limitation of relying solely on the EAM to infer medial joint loading when excessive directed cocontraction of muscles exists and call for further investigations into the soft tissue–related mechanisms that modulate the internal forces at the knee.

Objective: The LCS Complete mobile-bearing implant (LCS) is a widely used total knee replacement (TKR). Recently Norwegian (Gøthesen 2013) and American (Namba 2013) registry data has detected a lower survivorship of the LCS compared to other TKR. Specifically the relative risk for aseptic tibial[for full text, please go to the a.m. URL], Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2014)

Fragestellung: Die Kniebelastung, besonders die mediale Kniekontaktkraft Fmed, ist ein entscheidender Einflussfaktor für das Auftreten und Fortschreiten von Arthrose. Das einfach zu berechnende externe Adduktionsmoment (EAM) wird häufig als indirekte Messgröße für Fmed beim [for full text, please go to the a.m. URL], Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2014)

Fragestellung: Das Vibrationstraining ist ein Training, bei der Schwingungen in den Körper eingeleitet werden. Dabei sollen passiv Dehnreflexe der Muskulatur ausgelöst werden, um so die Muskulatur zu trainieren. Wie dieses Training jedoch tatsächlich die Muskeln trainiert und Faktoren[for full text, please go to the a.m. URL], Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2013)

Kenntnisse über die Belastung des Kniegelenks in vivo sind sowohl Grundlage für die präklinische Testung und Verbesserung von Implantaten als auch für die Validierung muskuloskeletaler Rechenmodelle. Des Weiteren ist das Wissen über die Belastung und über Möglichkeiten zur Entlastung des Gelenks entscheidend für die Behandlung von Patienten mit verschiedenen orthopädischen Indikationen wie Gonarthrose, Bandverletzungen, Meniskusschäden, gelenknahen Frakturen sowie nach Kniegelenksersatz. Instrumentierte Knieendoprothesen mit telemetrischer Datenübertragung ermöglichen die in vivo Messung der tibio- femoralen Kontaktkräfte und Momente. Im Rahmen dieser Arbeit erhielten neun Patienten mit Gonarthrose ein solches Implantat. Es zeigte sich, dass das Kniegelenk schon im Alltag großen Belastungen ausgesetzt ist. Bei den meisten alltäglichen Aktivitäten, wie z.B. Gehen und Treppen steigen, lag die Gesamtkraft zwischen 200 und 350% des Körpergewichts. Neben der Gesamtkraft im Kniegelenk spielt die medio-laterale Kraftverteilung eine entscheidende Rolle für die Entstehung und den Verlauf von Arthrose. Beim Gehen wird üblicherweise ein Großteil der maximalen Axialkraft über das mediale Kompartment übertragen. Dieses übernimmt zwischen 60 und 90% der gesamten Axialkraft. Konservative Methoden zur Behandlung medialer Arthrose, wie Valgus-Orthesen und laterale Schuhranderhöhungen sollen das mediale Kompartment entlasten und dadurch zu einer Schmerzreduktion führen. Eine Entlastung der medialen Kraft durch Schuhranderhöhungen war bei den untersuchten Probanden jedoch nur geringfügig um bis zu 7% möglich. Größere Entlastungen von 10-30% konnten, je nach Valgus- Stellung und Modell, durch Orthesen erreicht werden., Knowledge about the loading of the knee joint is essential for the preclinical testing of implants, validation and improvement of musculoskeletal models as well as for physicians, patients and physiotherapists. Since it is known that especially uni-compartmental loading contributes to the development and progression of osteoarthritis, information about the load distribution within the joint is crucial for the treatment of patients with orthopaedic indications such as osteoarthritis, meniscal lesions or total knee replacements. Instrumented knee implants with telemetric data transmission enable the measurement of tibio-femoral contact forces and moments in-vivo. In this study, the joint loading was measured in 9 patients during various activities of daily living. Moreover it was examined, weather it is possible to reduce the medial contact force using valgus braces or laterally wedged shoes. The results showed that the knee joint is already highly loaded during daily life. During most activities of daily living, such as walking and stair climbing, peak resultant forces between 200 and 350% of body weight were measured. The medio-lateral force distribution was strongly correlated to the leg alignment. Whereas in patients with a valgus-alignment the axial force was equally distributed between both compartments, about 80-90% of the axial force was transferred medially in patients with a varus-alignment. Using laterally wedged shoes, the medial contact force was reduced by up to 7% during walking. Larger reductions of 10-30% were, depending on model and valgus position of the brace, achieved by valgus braces.

Kenntnisse über die Belastung des Kniegelenks in vivo sind sowohl Grundlage für die präklinische Testung und Verbesserung von Implantaten als auch für die Validierung muskuloskeletaler Rechenmodelle. Des Weiteren ist das Wissen über die Belastung und über Möglichkeiten zur Entlastung des Gelenks entscheidend für die Behandlung von Patienten mit verschiedenen orthopädischen Indikationen wie Gonarthrose, Bandverletzungen, Meniskusschäden, gelenknahen Frakturen sowie nach Kniegelenksersatz. Instrumentierte Knieendoprothesen mit telemetrischer Datenübertragung ermöglichen die in vivo Messung der tibio- femoralen Kontaktkräfte und Momente. Im Rahmen dieser Arbeit erhielten neun Patienten mit Gonarthrose ein solches Implantat. Es zeigte sich, dass das Kniegelenk schon im Alltag großen Belastungen ausgesetzt ist. Bei den meisten alltäglichen Aktivitäten, wie z.B. Gehen und Treppen steigen, lag die Gesamtkraft zwischen 200 und 350% des Körpergewichts. Neben der Gesamtkraft im Kniegelenk spielt die medio-laterale Kraftverteilung eine entscheidende Rolle für die Entstehung und den Verlauf von Arthrose. Beim Gehen wird üblicherweise ein Großteil der maximalen Axialkraft über das mediale Kompartment übertragen. Dieses übernimmt zwischen 60 und 90% der gesamten Axialkraft. Konservative Methoden zur Behandlung medialer Arthrose, wie Valgus-Orthesen und laterale Schuhranderhöhungen sollen das mediale Kompartment entlasten und dadurch zu einer Schmerzreduktion führen. Eine Entlastung der medialen Kraft durch Schuhranderhöhungen war bei den untersuchten Probanden jedoch nur geringfügig um bis zu 7% möglich. Größere Entlastungen von 10-30% konnten, je nach Valgus- Stellung und Modell, durch Orthesen erreicht werden., Knowledge about the loading of the knee joint is essential for the preclinical testing of implants, validation and improvement of musculoskeletal models as well as for physicians, patients and physiotherapists. Since it is known that especially uni-compartmental loading contributes to the development and progression of osteoarthritis, information about the load distribution within the joint is crucial for the treatment of patients with orthopaedic indications such as osteoarthritis, meniscal lesions or total knee replacements. Instrumented knee implants with telemetric data transmission enable the measurement of tibio-femoral contact forces and moments in-vivo. In this study, the joint loading was measured in 9 patients during various activities of daily living. Moreover it was examined, weather it is possible to reduce the medial contact force using valgus braces or laterally wedged shoes. The results showed that the knee joint is already highly loaded during daily life. During most activities of daily living, such as walking and stair climbing, peak resultant forces between 200 and 350% of body weight were measured. The medio-lateral force distribution was strongly correlated to the leg alignment. Whereas in patients with a valgus-alignment the axial force was equally distributed between both compartments, about 80-90% of the axial force was transferred medially in patients with a varus-alignment. Using laterally wedged shoes, the medial contact force was reduced by up to 7% during walking. Larger reductions of 10-30% were, depending on model and valgus position of the brace, achieved by valgus braces.