Evaluation of laxity tests with a musculoskeletal model of total knee arthroplasty

Introduction Musculoskeletal models are emerging as potential tools for the use in many clinical applications. One important example is aid to the clinical decision in the orthopaedic field. Recently, a patient-specific model of Cruciate-Retaining Total Knee Arthroplasty (CR-TKA) was presented and validated with respect to knee joint forces and kinematics [1]. However, the ligament restraints were not calibrated and inaccuracies in knee kinematic predictions were present. The objective of this study was to evaluate the effect of ligament calibration on the performance of simulated laxity tests. Methods A musculoskeletal model of CR-TKA was previously described [1]. The model comprised the musculoskeletal architecture of a TKA patient and a force-dependent model of the prosthetic knee and patellofemoral joint. Ligament restraints were modelled using non-linear springs and contact was solved using a rigid formulation. To calibrate the ligament parameters we simulated anterior/posterior, valgus/varus and endo-/exorotation laxity tests. Each test was performed at four different knee flexion angles (0, 30, 60, 90 deg). The anterior (respectively posterior) laxity load consisted of a 35 N force applied on the tibia at a distance of approximately 15 cm from the surface of the tibial component, pointing anteriorly (respectively posteriorly). Valgus (respectively varus) test was simulated by applying a force on the tibia at a distance of approximately 15 cm from the ankle joint, pointing laterally (respectively medially) so that the resulting moment was equal to 10 Nm. For the endo- (respectively exo-) rotation a 1.5 Nm torque was applied to the longitudinal axis of the tibia. Laxity envelopes for each test were calculated as the difference between the values obtained in the two opposite directions of the test. Manual changes to ligament insertion site, stiffness, and reference strain were made iteratively in order to obtain laxity envelopes close to those reported in the literature for cadaveric tests on a CR-TKA [2]. All the laxity tests were eventually simulated with the same ligament configuration. Results The results for all simulated laxity tests and the reference values from the literature are summarized in Table 1. 0° 30° 60° 90° AP (M) 3.5mm 4.2mm 1.0mm 1.0mm AP (L) 1.5mm 5mm 4mm 4.5mm VV (M) 0.9° 4.3° 2.6° 1.5° VV (L) 3.0° 6.0° 7.0° 7.0° EE (M) 7.0° 16.5° 4.0° 5.5° EE (L) 6.5° 22.0° 21.0° 23.0° Table 1: AP: Anterior/Posterior, VV: Valgus/Varus, EE: Endo-/Exorotation, M: Model prediction, L: Literature value Discussion The laxity envelopes predicted by the model were in partial agreement with those reported in the literature. The largest differences were noted for 60-90 degrees of knee flexion for all laxity tests, where the model showed considerably less laxity. These deviations may be attributable to actual differences between the implant design and subject geometry currently simulated and those used in the cadaveric tests. In future studies we aim to simulate surgical variations such as implant size and positioning, joint line elevation and ligament restraint. This musculoskeletal model of TKA has potential as a pre-operative planning tool for orthopaedic interventions. References Marra et al, J Biomech Eng, 137, 2015 Saeki et al, Clin Orthop Relat Res, 392:184-189, 200

Job Mobility and Sorting: Theory and Evidence

I derive a measure of job mobility that reflects individuals ability to sort into the preferred jobs. Relying on the Survey of Income and Program Participation, I find that educational attainment tends to have a strong positive effect on internal (i.e., within firms) and external (i.e., between firms) job mobility. General experience and occupation-specific human capital have only a limited effect on both internal and external mobility. The impact of being versatile on an individual s external job mobility is substantial and similar in magnitude as the effect of a college degree on a high school dropout s external mobility

Beyond health:medicines, food supplements, energetics, and the commodification of self-performance in Maputo

With an increasing range of products in global and local markets, more options are available for individuals to enhance their image and their (cognitive, social and physical) performance. These ‘performance consumptions’ relate to ideals of well‐being and improvement, and are based on constructed desires, expectations and needs that go beyond the (often blurred) dichotomy of health and illness. Drawing from mixed‐methods research in Maputo, Mozambique, this paper discusses individuals’ use of medicines and other substances – pharmaceuticals, food supplements, traditional herbs, cosmetics and energy drinks – for managing different aspects of their everyday lives. Through an overview of the main consumption practices, we explore the underlying purposes and strategies of users, and the perceived legitimacy and risks involved when using a variety of products accessible through formal and informal exchange channels. From tiredness to sexual and aesthetic management, we show how the body becomes the locus of experimentation and investment to perform in accordance with socially expected roles, individual aspirations and everyday tasks. With insights from individuals’ accounts in Maputo, we aim to add to discussions on pharmaceuticalisation of body management by showing how the emergence of new performance consumptions is articulated with the reconfiguration of more ‘traditional’ consumption practices.info:eu-repo/semantics/acceptedVersio

Calling Gaia: World Brains and Global Memory

‘See the world we come from. There is no green there. They killed their mother. And they are gonna do the same here’. This is earthling Jake Sully speaking to Eywa, the Gaia-like goddess and balancing force of the ecosystem of the planetoid Pandora. At a dramatic narrative juncture of the film Avatar (James Cameron 2009), Jake calls on Eywa to intervene in the battle between the Na’vi, the tall and blue-skinned native inhabitants of Pandora, and the military forces of the Resources Development Agency (RDA) from Earth that colonize the planet. Having just learned from a fellow resistance fighter that the fibre-optic lianas of the so-called Tree of Voices provide a ‘direct line to Eywa’, Jake connects his native avatar’s neural queue to one of the threads and starts to talk. He urges Eywa to access the memories of his deceased colleague Dr. Grace Augustine in order to get an impression of the destruction that humans have inflicted upon the ecosystem of their own planet. Against all odds, the distress call is answered. From the depths of Pandora’s jungles Eywa sends herds of dinosaur-like creatures that launch a counter attack and run over the RDA war machine. The ecosystem strikes back and the invaders are sent home to Earth

Kneeling and standing up from a chair as performance-based tests to evaluate knee function in the high-flexion range: a randomized controlled trial comparing a conventional and a high-flexion TKA design

Contains fulltext : 177055.pdf (publisher's version ) (Open Access)BACKGROUND: We compared the functional outcome between conventional and high-flexion total knee arthroplasty (TKA) using kneeling and sit-to-stand tests at 1 year post-operative. In addition, the patient's daily functioning, pain and satisfaction were quantified using questionnaires. METHODS: We randomly assigned 56 patients to receive either a conventional or a high-flexion TKA. Primary outcomes were maximum flexion angle and maximum thigh-calf contact measured during kneeling at 1 year post operatively. Secondary outcomes were the angular knee velocity and ground reaction force ratio measured during sit-to-stand performance tests, and questionnaires. RESULTS: At one year post-operative, maximum knee flexion during kneeling was higher for the high-flexion TKA group (median 128.02 degrees (range 108-146)) compared to the conventional TKA group (119.13 degrees (range 72-135)) (p = 0.03). Maximum thigh-calf contact force was higher for the high flexion TKA group (median 17.82 N (range 2.98-114.64)) compared to the conventional TKA group (median 9.37 N (range 0.33-46.58))(p = 0.04). The sit-to-stand tests showed a significantly higher angular knee velocity in the conventional TKA group (12.12 rad/s (95%CI 0.34-23.91); p = 0.04). There were no significant differences between groups in ground reaction force ratios and patient-reported outcome scores. CONCLUSION: Although no differences were found in patient-reported outcome scores, differences in performance-based tests were clearly apparent. Standing up from a chair at 90 degrees of knee flexion appeared to be easier for the conventional group. The kneeling test revealed significantly higher weight-bearing knee flexion for the high-flex group. Hence, if kneeling is an important activity for a patient a high-flex design may be recommendable. TRIAL REGISTRATION: The study was retrospectively registered in ClinicalTrials.gov under identifier NCT00899041 (date of registration: May 11, 2009)

Dutch translation and validation of the Norwich Patellar Instability score and Banff Patella Instability Instrument in patients after surgery for patellar instability

Item does not contain fulltex