MRI Sequence Influences Geometrical Information of Osseous Tissues

Although CT-scan data gives accurate geometrical information of bones, MRI data is commonly used instead due to its non-ionizing nature. The geometrical information has a number of applications, including image registration and computer simulations of the human joints, presurgical planning, prosthesis design, linking geometry with function and pain and kinematics. Hence, it is important to for the geometrical information extracted from the MRI data to be accurate. However, this information is influenced by the choice of the MRI sequence. Therefore, the aim of this study is to investigate the effect of different MRI sequences on the accuracy of geometrical information of bones

Development and validation of a computational model of the knee joint for the evaluation of surgical treatments for osteoarthritis

A three-dimensional (3D) knee joint computational model was developed and validated to predict knee joint contact forces and pressures for different degrees of malalignment. A 3D computational knee model was created from high-resolution radiological images to emulate passive sagittal rotation (full-extension to 658-flexion) and weight acceptance. A cadaveric knee mounted on a six-degree-of-freedom robot was subjected to matching boundary and loading conditions. A ligamenttuning process minimised kinematic differences between the robotically loaded cadaver specimen and the finite element (FE) model. The model was validated by measured intra-articular force and pressure measurements. Percent full scale error between FE-predicted and in vitro-measured values in the medial and lateral compartments were 6.67% and 5.94%, respectively, for normalised peak pressure values, and 7.56% and 4.48%, respectively, for normalised force values. The knee model can accurately predict normalised intra-articular pressure and forces for different loading conditions and could be further developed for subject-specific surgical planning

The development and evaluation of a 3-dimensional, image-based, patient-specific, dynamic model of the hindfoot

This study developed subject-specific, three-dimensional dynamic hindfoot models (1 in vivo, 1 in vitro) using 3D stress MRI data. Each model’s ability to capture mechanical phenomena including those of the healthy hindfoot and the hindfoot with ligament injury was evaluated through subject-specific experimental mechanical analyses (using an arthrometer and a stress MRI technique). Existing software (3DVIEWNIXTM) was incorporated with software developed in-house (marching cubes program) to obtain the subject’s bone surface geometry, collateral and subtalar ligament insertion data. The bone surface data were then imported into a reverse engineering software package (Geomagic StudioTM) to obtain CAD representations for the bone geometries. The ligaments’ non-linear structural properties were obtained directly from an existing experimental study or were estimated. Contact forces between bones were modeled using cartilage’s Elastic Modulus and an exponential term to imitate its non-linear compression characteristics. The ADAMS 2003TM dynamic simulation software generated and solved the dynamic equations of motion under the forcing functions and boundary conditions. The in vivo experimental kinematic data were smaller than those predicted by the model. This indicates that surrounding soft tissues excluding the ligaments may decrease joint range of motion. The in vitro model captured the experimental kinematic patterns of the ankle joint complex, but did so by under-estimating ankle joint motion and over-estimating subtalar joint motion. Better knowledge of the ankle joint and subtalar joint ligament structural properties is necessary. Similar to experimental data, the in vivo and in vitro models’ ankle joint complex had non-linear load-displacement properties in all directions. They are dependent on the contact of the articulating surfaces and ligament constraints. Sensitivity analyses indicated that kinematic changes caused by altering ligament geometry are smaller than changes caused by lateral ligament removal; therefore the model may be sensitive to predicting the changes that occur during ligament rupture. The models’ assumptions and limitations include differences between the experimental and modeled boundary conditions, exclusion of the cartilage geometry, estimation of the contact damping coefficient, the contact stiffness and penetration exponent, estimation of the subtalar ligaments’ structural properties, generalized non-linear properties for the collateral ligaments, and soft-tissue motion during the experiments. Future work must focus on developing a larger group of patient-specific models so that the output data has sufficient statistical power.Ph.D., Mechanical Engineering -- Drexel University, 200

Fixed-bearing Medial Unicompartmental Knee Arthroplasty Restores Neither the Medial Pivoting Behavior Nor the Ligament Forces of the Intact Knee in Passive Flexion

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non-conforming, fixed bearing medial UKA affects tibiofemoral kinematics and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior-posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° flexion, but occurred from 30° to 90° flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non-conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion

Q fever in Bulgaria and Slovakia.

As a result of dramatic political and economic changes in the beginning of the 1990s, Q-fever epidemiology in Bulgaria has changed. The number of goats almost tripled; contact between goat owners (and their families) and goats, as well as goats and other animals, increased; consumption of raw goat milk and its products increased; and goats replaced cattle and sheep as the main source of human Coxiella burnetii infections. Hundreds of overt, serologically confirmed human cases of acute Q fever have occurred. Chronic forms of Q fever manifesting as endocarditis were also observed. In contrast, in Slovakia, Q fever does not pose a serious public health problem, and the chronic form of infection has not been found either in follow-ups of a Q-fever epidemic connected with goats imported from Bulgaria and other previous Q-fever outbreaks or in a serologic survey. Serologic diagnosis as well as control and prevention of Q fever are discussed

Reproducibility in modeling and simulation of the knee:Academic, industry, and regulatory perspectives

Stakeholders in the modeling and simulation (M&amp;S) community organized a workshop at the 2019 Annual Meeting of the Orthopaedic Research Society (ORS) entitled “Reproducibility in Modeling and Simulation of the Knee: Academic, Industry, and Regulatory Perspectives.” The goal was to discuss efforts among these stakeholders to address irreproducibility in M&amp;S focusing on the knee joint. An academic representative from a leading orthopedic hospital in the United States described a multi-institutional, open effort funded by the National Institutes of Health to assess model reproducibility in computational knee biomechanics. A regulatory representative from the United States Food and Drug Administration indicated the necessity of standards for reproducibility to increase utility of M&amp;S in the regulatory setting. An industry representative from a major orthopedic implant company emphasized improving reproducibility by addressing indeterminacy in personalized modeling through sensitivity analyses, thereby enhancing preclinical evaluation of joint replacement technology. Thought leaders in the M&amp;S community stressed the importance of data sharing to minimize duplication of efforts. A survey comprised 103 attendees revealed strong support for the workshop and for increasing emphasis on computational modeling at future ORS meetings. Nearly all survey respondents (97%) considered reproducibility to be an important issue. Almost half of respondents (45%) tried and failed to reproduce the work of others. Two-thirds of respondents (67%) declared that individual laboratories are most responsible for ensuring reproducible research whereas 44% thought that journals are most responsible. Thought leaders and survey respondents emphasized that computational models must be reproducible and credible to advance knee M&amp;S.</p