No abstract

Strain energy-based adaptive material models are used to predict bone resorption resulting from stress shielding induced by prosthetic joint implants. Generally, such models are governed by two key parameters: a homeostatic strain-energy state (K) and a threshold deviation from this state required to initiate bone reformation (s). A refinement procedure has been performed to estimate these parameters in the femur and glenoid; this study investigates the specific influences of these parameters on resulting density distributions in the distal ulna. A finite element model of a human ulna was created using micro-computed tomography (µCT) data, initialized to a homogeneous density distribution, and subjected to approximate in vivo loading. Values for K and s were tested, and the resulting steady-state density distribution compared with values derived from µCT images. The sensitivity of these parameters to initial conditions was examined by altering the initial homogeneous density value. The refined model parameters selected were then applied to six additional human ulnae to determine their performance across individuals. Model accuracy using the refined parameters was found to be comparable with that found in previous studies of the glenoid and femur, and gross bone structures, such as the cortical shell and medullary canal, were reproduced. The model was found to be insensitive to initial conditions; however, a fair degree of variation was observed between the six specimens. This work represents an important contribution to the study of changes in load transfer in the distal ulna following the implementation of commercial orthopedic implants.

The accurate assessment of symmetry in the craniofacial skeleton is important for cosmetic and reconstructive craniofacial surgery. Although there have been several published attempts to develop an accurate system for determining the correct plane of symmetry, all are inaccurate and time consuming. Here, the authors applied a novel semi-automatic method for the calculation of craniofacial symmetry, based on principal component analysis and iterative corrective point computation, to a large sample of normal adult male facial computerized tomography scans obtained clinically (n = 32). The authors hypothesized that this method would generate planes of symmetry that would result in less error when one side of the face was compared to the other than a symmetry plane generated using a plane defined by cephalometric landmarks. When a three-dimensional model of one side of the face was reflected across the semi-automatic plane of symmetry there was less error than when reflected across the cephalometric plane. The semi-automatic plane was also more accurate when the locations of bilateral cephalometric landmarks (eg, frontozygomatic sutures) were compared across the face. The authors conclude that this method allows for accurate and fast measurements of craniofacial symmetry. This has important implications for studying the development of the facial skeleton, and clinical application for reconstruction.

Compared to experimental studies using strain gauges, finite element (FE) models are not limited to strain measurements at discrete locations and can be used to examine the continuous strain and stress field throughout bone. As such, they can be a useful tool for biomechanical investigations interested in stress and strain changes as a result of multiple loading conditions, implant designs, etc. Critical to their development is the assignment of material properties.

The ability for operators to make operational and maintenance decisions based on in-line inspection (ILI) data depends on the performance of ILI tools with respect to sizing and detection of crack and stress corrosion cracking (SCC) features. A series of previous Pipeline Research Council International, Inc. (PRCI) projects created a database of ILI tool and pipe excavation data that can be used to evaluate the detection and sizing capabilities of ultrasonic (UT) (NDE-4-E Phase 1, PR-244-133731) and electromagnetic acoustic (EMAT) (NDE-4-E Phase 2, PR-244-153719) ILI technologies. This current project, NDE-4-7 (PR-244-173856), was carried out by C-FER Technologies (1999) Inc. (C-FER) for PRCI. It is Phase 3 of an ongoing industry-wide effort to understand and characterize ILI tool performance. In addition to adding a new data set to the database developed in Phases 1 and 2, estimates of ILI tool performance with respect to rate of detection (ROD), probability of identification (POI), false discovery rate (FDR), and sizing accuracy (SA) were calculated. Two further analyses were performed, namely an investigation of the effect of crack profile data on tool performance and burst pressure estimation, and an evaluation of the reduction in sizing uncertainty attained through multiple measurements of crack features. This document has a related webinar.