Phase diagram of brittle fracture in the semi-grand-canonical ensemble.

We present a simulation method to assess the quasistatic fracture resistance of materials. Set within a semi-grand-canonical Monte Carlo (SGCMC) simulation environment, an auxiliary field-the bond rupture potential-is introduced to generate a sufficiently large number of possible microstates in the semi-grand-canonical ensemble, and associated energy and bond fluctuations. The SGCMC approach permits identifying the full phase diagram of brittle fracture for harmonic and nonharmonic bond potentials, analogous to the gas-liquid phase diagram, with the equivalent of a liquidus line ending in a critical point. The phase diagram delineates a solid phase, a fractured phase, and a gas phase, and provides clear evidence of a first-order phase transition intrinsic to fracture. Moreover, energy and bond fluctuations generated with the SGCMC approach permit determination of the maximum energy dissipation associated with bond rupture, and hence of the fracture resistance of a widespread range of materials that can be described by bond potentials.

Reverse shoulder arthroplasty has a higher risk of revision due to infection than anatomical shoulder arthroplasty: 17 730 primary shoulder arthroplasties from the Nordic Arthroplasty Register Association.

AIMS: The aim of this study was to use national registry database information to estimate cumulative rates and relative risk of revision due to infection after reverse shoulder arthroplasty. PATIENTS AND METHODS: We included 17 730 primary shoulder arthroplasties recorded between 2004 and 2013 in The Nordic Arthroplasty Register Association (NARA) data set. With the Kaplan-Meier method, we illustrated the ten-year cumulative rates of revision due to infection and with the Cox regression model, we reported the hazard ratios as a measure of the relative risk of revision due to infection. RESULTS: In all, 188 revisions were reported due to infection during a mean follow-up of three years and nine months. The ten-year cumulative rate of revision due to infection was 1.4% overall, but 3.1% for reverse shoulder arthroplasties and 8.0% for reverse shoulder arthroplasties in men. Reverse shoulder arthroplasties were associated with an increased risk of revision due to infection also when adjusted for sex, age, primary diagnosis, and year of surgery (relative risk 2.41 (95% confidence interval 1.26 to 5.59); p = 0.001). CONCLUSION: The overall incidence of revision due to infection was low. The increased risk in reverse shoulder arthroplasty must be borne in mind, especially when offering it to men. Cite this article: Bone Joint J 2019;101-B:702-707.

Cardiovascular risk factors in an Iranian urban population: Tehran lipid and glucose study (phase 1).

OBJECTIVES: Coronary artery disease is becoming more prevalent in developing countries, particularly in urban areas. This study was conducted to determine the prevalence of cardiovascular risk factors among Tehran urban population. METHODS: The prevalence and distribution of high blood pressure, cigarette smoking, dyslipoproteinemia, diabetes mellitus, and obesity was determined in 15,005 subjects, aged three years and over, selected by cluster random sampling in Tehran urban district-13 between February 1999 to August 2001. Total energy intake, percent of energy derived from protein, carbohydrate, and fat were assessed in a subsidiary of 1,474 persons by means of two 24-hour dietary recalls. RESULTS: In adults, 78% of men and 80% of women presented at least one CVD risk factor. The percentage of adult women with two or more risk factors was significantly greater than the one for men. Prevalence of DM, hypertension, obesity, high TC, low HDL, high TGs, and smoking was 9.8, 20.4, 14.4, 19.3, 32, 5.3, and 22.3%, respectively. In children and adolescents, two or more CVD risk factors were found in 9% of boys and 7% of girls. Prevalence of hypertension, obesity, high TC, low HDL, and high TGs, was 12.7, 5.2, 5.1, 10.2, and 5%, respectively. The mean percentage values of energy intake derived from carbohydrate, protein, and fat were 57.8 +/- 6.9, 11.1 +/- 1.8, and 30.9 +/- 7.2, respectively. CONCLUSION: The prevalence of cardiovascular risk factors among Tehran urban population is high; particularly of high total cholesterol, low HDL cholesterol levels, and high waist to hip ratio. An effective strategy for life style modification is a cornerstone of a population approach to the cardiovascular risk factors. Moreover, these results will serve as a baseline for assessment of future trends in the risk factors studied.

Reconstruction after multilevel corpectomy in the cervical spine. A sagittal plane biomechanical study.

STUDY DESIGN: An in vitro biomechanical study of reconstruction techniques used after multilevel cervical corpectomy. OBJECTIVES: To determine the biomechanical behavior of the cervical spine after a multilevel corpectomy and reconstruction with a strut graft and supplementation of the graft with anterior and posterior plates. SUMMARY OF BACKGROUND DATA: Reconstruction of the spine after multilevel corpectomy represents a significant challenge, with nonunion or graft dislodgment being relatively common. Anterior and posterior plate fixation have increased the possibilities for supplemental stabilization. Although some clinical studies have been performed to examine multilevel corpectomies reconstructed with plates, biomechanical studies are few and are limited to single-segment models. METHODS: Flexibility testing was performed on 11 intact cervical spine preparations. Flexibility testing was also conducted on the spine preparations after reconstruction with a strut graft, after supplementation of the graft with an anterior plate, and after supplementation of the graft with lateral mass plates. Physiologic moments were applied dynamically, and the three-dimensional motion of the specimen was recorded with stereophoto-grammetry. Failure testing was performed on the plated specimens in compression. Load displacement curves and failure modes were analyzed. RESULTS: The range of motion after reconstruction compared with the control was decreased 24% after strut grafting, 43% after application of an anterior plate, and 62% after application of posterior plates. Similarly, flexibility coefficients showed that the posterior plate technique was the least flexible, followed by the anterior plate technique, with the graft alone being the most flexible reconstruction construct. Load to initial failure tended to be higher in posterior than in anterior plate specimens, and screw pullout was the predominant failure mode. CONCLUSIONS: The application of plates to the cervical spine as an adjunct to bone graft may improve the surgeon's ability to stabilize the spine after multilevel corpectomy. Understanding the biomechanics of these devices and the potential mode of failure is important in their use.

Effects of kyphosis and lordosis on the remaining lumbar vertebral levels within a thoracolumbar fusion: an experimental study of the multisegmental human spine.

This study was done to determine the motion of the whole lumbar spine after internal fixation and the effect of kyphosis and lordosis on the remaining vertebral levels. Baseline motion analysis of sagittal, frontal, and transverse planes was done to determine the intact range of motion. Three fusion configurations were tested: neutral position (0 degrees), 4.6 degrees +/- 2.0 kyphosis, and -6.2 degrees +/- 3.6 lordosis. The sagittal and frontal plane relative rotation of the instrumented segments (T12/L2) decreased an average of 74% and 60%, respectively, as compared with intact testing. Sagittal plane motion at the remaining segments increased for all fusion configurations when compared with intact motion and reached statistical significance at the L4/L5 level. No significant differences were found between fusion configurations (ie, fused neutral, kyphosis, and lordosis).

Intervertebral spacer as an adjunct to anterior lumbar fusion. Part I. Design, fabrication, and testing of three prototypes.

Failure of anterior lumbar fusions are common, because the bone graft is required to provide mechanical stability during creeping substitution and replacement with host bone. Support of the interspace with mesh, cages, plates, and rods results in an improved rate of fusion. The objective of this study was to develop an anterior interbody implant to stabilize adjacent vertebral segments during spinal fusion. Three prototypes of an intervertebral spacer for anterior lumbar stabilization were designed, fabricated, and tested in vitro. The implants were inserted vertically between adjacent vertebral bodies in fresh frozen cadaver swine and baboon spines after disc excision and vertebral body preparation. In vitro cyclic testing of the three prototypes implanted in porcine and baboon spines to 100,000 cycles showed no displacement of the implant at 560-N axial and 16-Nm torsional loading. Three-point bending cyclic fatigue testing of the porous coated cylindrical implants (prototype 3) showed a maximum strength of 9,700 N in axial compressions. Analysis of the motion profiles at the site of implantation confirmed less axial displacement at the implant level compared with the uninstrumented levels above and below, but similar torsional displacements. Biomechanical testing of the three prototypes of anterior implants as well as radiographic, microstructural, and motion analysis confirmed implant stability and structural integrity in vitro. Based on these findings, implantation of a porous coated implant in baboons was undertaken as described in Part II (Nasca et al., this issue).

Intervertebral spacer as an adjunct to anterior lumbar fusion. Part II. Six-month implantation in baboons.

Failure of interbody fusions in the lumbar spine are common due to reliance on the graft for structural support during healing by creeping substitution. Support of the interspace with an implant should result in improved fusion success. The objective of this study was to evaluate the stability of the implant in vivo and its potential as an adjunct to promote interbody arthrodesis. Prototype 3, a porous coated intervertebral spacer with extension lugs made of Ti-6A1-4V, was implanted vertically between adjacent lumbar vertebrae anteriorly in four baboons undergoing anterior interbody fusion. The animals were allowed freedom of activity for 6 months before being killed. A transperitoneal approach was made exposing the L4-L5 or L5-L6 interspace. At time of killing, clinical evaluation of the implant-vertebral body construct showed stability to manual stresses applied in extension, flexion, and rotation. Serial radiographs taken during the 6 months of implantation showed no change in position or displacement of the implants. Axial and torsional cyclic loads were applied to each spine at 1 cycle/s for 20,000 cycles. Statistical analysis of the motion profiles for intact and implanted spines demonstrated no significant difference in axial or rotational displacements at the arthrodesis level or adjacent unoperated levels, L1 and L4. The in vivo 6-month study in baboons confirmed implant stability and maintenance of disc space height. Variable osseous healing was noted. Release of plasma spray beading may have resulted from improper application on the implant or micromotion within the construct. A better method to mechanically interlock the plungers is being studied. Clinical trials based on this work appear justified.

Investigation of video techniques for dynamic measurements of relative vertebral-body motion in vitro.

The precision and accuracy of techniques for analysis of lumbar spinal-segment motions were evaluated using a specially designed orthogonal axis fixture and video image processing. Triplicate validation tests were performed by monitoring precisely controlled motions of the triaxial measurement device. The errors of the overall measurements were found to be less than 0.5 mm for axial and 1 degree for rotational displacements. The system accuracy was within 0.230 mm based on the calculation of the points on a calibration frame. The geometry of the calibration frame was designed with the capability to analyze the 3-D motion properties of a swine lumbar spine. Statistical analyses of the validation test data showed that the precision and accuracy of this motion-analysis system offer new opportunities for the measurement of total-length spinal-motion profiles. The system was then applied utilizing fresh thawed swine spines to test the limits of relative-motion measurements for the centers of adjacent vertebrae in a coupled unit. Lateral-medial and anterior-posterior video images of spines and the triaxial measurement devices were made simultaneously while applying cyclic axial and torsional loads. The distribution of data from six spines illustrated biological variability of relative displacements for adjacent coupled vertebrae.

Increase of motion between lumbar vertebrae after excision of the capsule and cartilage of the facets. A cadaver study.

Seventeen fresh segments of cadaveric lumbar spines were tested in flexion, extension, and axial rotation. The resulting angular rotations were measured with the use of a goniometer and a three-dimensional system of video analysis. Measurements of flexibility were made, in order, in the intact spine; after decompression (bilateral total laminectomies, partial medial facetectomies, and foraminotomies); after excision of the capsule and cartilage of the facets; and after cancellous bone had been packed into the facet defects. Decompression resulted in a slight increase in the sagittal and axial ranges of motion. Subsequent excision of the capsule and cartilage of the facets, as in preparation for an arthrodesis of the facets, resulted in a significant increase in both the sagittal (5.7 +/- 2.9 degrees, mean and standard deviation) (p < 0.001) and the axial (1.4 +/- 0.9 degrees) (p < 0.01) ranges of motion compared with the motion in the intact specimen and with the motion in the specimen after only decompression had been done (p < 0.01 and p < 0.05, respectively). Packing of bone in the facets did not significantly reduce motion. It was calculated that the increase in the sagittal range of motion after excision of the capsule and cartilage of the facets would increase the tensile strain in a graft between the transverse processes of the fourth and fifth lumbar vertebrae (18 +/- 1 per cent tensile strain [mean and 95 per cent confidence interval] for the intact vertebrae and 25 +/- 1 per cent for the vertebrae in which the facets had been excised).

The design of a microcomputer-controlled voice onset time analyzer.

In spoken syllables such as "ta," the interval between the release of the tongue constriction for the stop consonant /t/ and the onset of the vowel is called voice onset time, or VOT. Voice onset time is an important determinant of whether the initial consonant will be heard as a /t/(values of 60-90 ms) or as a /d/ (values of 0-30 ms). VOT information, immediately following a spoken syllable, can provide a speaker with feedback for modifying speech production. Such information can help the hearing-impaired learn to speak. It may also help people who learn English as a second language, since they often produce /b,d,g/ and /p,t,k/ with inappropriate VOT values. A prototype portable device measures VOT for initial voiced and voiceless stop consonants (e.g., "da" and "ta"). A dual-microphone method is used for acoustic measurement. A microphone in front of the mouth picks up the radiated acoustic signal; another over the larynx transduces vocal vibrations that mark the beginning of a vowel. Analog circuits process the transducer signals and provide gain and filtering. Filters were designed on the basis of the acoustic properties of stop consonants. The output from each analog circuit is fed to a comparator that compares the signal level with a fixed threshold voltage reference. A digital timer starts when the amplitude of the oral signal voltage exceeds a threshold and stops when the laryngeal signal voltage exceeds a threshold. VOT values obtained by the device were compared with those made from digital waveforms of words spoken by five talkers.(ABSTRACT TRUNCATED AT 250 WORDS)