Analytical Limit Load Procedure for The Axial Complex Shaped Defect in a Pressurized Pipe

The paper is devoted to elaboration of the analytical O-procedure for limit load analysis of complex shaped axial defect in a pressurized pipe. It is based on the classical lower bound theorem of the theory of plasticity, and consists in construction of the statically admissible solution, where distribution of stress satisfies to the equilibrium equations and strength conditions. O-procedure is an optimization process to get the most favorable stress distribution for providing the maximal pressure. It allows to explicitly account for the variable geometrical and physical parameters. Contrary to other approaches, the derived formula for rectangular defect is only a particular case of the general procedure application. Four different methods for the complex defects are compared. They are: first, ASME, A-, rectangular defect formula combined with RSTRENG, R-, procedure, i.e., A-R approach; second, PCORRC, P-, formula with R-procedure, P-R approach; third, Orynyak's, O-, formula with R-procedure, O-R approach; and fourth, our universal O-procedure. The verification begins for rectangular defects where both theoretical and experimental comparison is performed for A-, P-, and O- formulas. The difference between them is small, provided that all three employ the same characteristic of material, here the ultimate strength. Then theoretical comparison for A-R, P-R, O-R approaches and O-procedure is performed for the artificial complex defects, for two symmetrical rectangular defects, for triangular defect. Experimental comparison between four methods is made based on the well-known University of Waterloo full scale tests.

Update on the Biomechanics of the Craniocervical Junction, Part II: Alar Ligament

Study Design: In vitro biomechanical study. Objective: The strength of the alar ligament has been described inconsistently, possibly because of the nonphysiological biomechanical testing models, and the inability to test the ligament with both attachments simultaneously. The purpose of this biomechanical model was to reevaluate the alar ligament’s tensile strength with both bony attachments, while also keeping the transverse ligament intact, all in a more physiological biomechanical model that mimics the mechanism of traumatic injury closely. Methods: Eleven fresh-frozen occipito-atlanto-axial (C0-C1-C2) specimens were harvested from individuals whose mean age at death was 77.4 years (range 46-97 years). Only the alar and transverse ligaments were preserved, and the bony C0-C1-C2 complex was left intact. Axial tension was exerted on the dens to displace it posteriorly, while the occipito-axial complex was fixed anteriorly. A device that applies controlled increasing force was used to test the tensile strength (M2-200, Mark-10 Corporation). Results: The mean force required for the alar ligament to fail was 394 ± 52 N (range 317-503 N). However, both the right and left alar ligaments ruptured simultaneously in 10 specimens. The ligament failed most often at the dens (n = 10), followed by occipital condyle rupture (n = 1). The transverse ligament remained intact in all specimens. Conclusions: When both the right and left alar ligament were included, the total alar ligament failure occurred at an average force of 394 N. The alar ligament failed before the transverse ligament.

Embryogenesis of an Invertebrate Lymphoid Organ: The Asterina Gibbosa Axial Organ (Asterids, Echinodermata)

The metamerization of the coelom leads to the axial complex genesis. Mesodermic cells appear besides the stone canal (larva 12 days old): they constitute the axial organ (AO) which develop, in the ventral side, the oral part (PO). This last part corresponds (sensu stricto) to the ancestral lymphoïd organ.

20 Cervical Spine Fragility Fractures in Older People: 5-Year Experience At A Regional Spine Centre

Introduction Cervical spine fractures are particularly prevalent in older people and commonly occur following a fall from standing height or less, in the presence of degenerative spinal disease. Atlanto-axial complex and odontoid process injuries are the most frequent type of fractures and are potentially life threatening. Published in-hospital and 1-year mortality rates in older people are eightfold higher than in younger patients. The aim of this study was to identify the incidence and characteristics of cervical spine fractures in older people presenting to a regional spine centre. Methods Clinical records and radiographs were retrospectively reviewed using our institutional registry covering a 5-year period. Data included patient age, gender, mechanism of trauma, level of fracture, stability of the fracture, treatment modality, imaging modality, and mortality rates. Results A total of 209 patients above the age of 70 with cervical spine fractures were treated in our centre from 2015-2019. The mean age of the patients at the time of injury was (82.4 ±7.5) years with the majority (n=117; 56%) being females. One-hundred fifty-one patients (72.2%) experienced fractures in the atlanto-axial complex. Particularly, Dens fractures were the most commonly reported fracture (n=119; 56.9%). Most of the patients encountered stable cervical spine fractures (n=181; 86.6%) and these were managed by external immobilization with hard collar or halo vest. Mechanism of trauma was divided into two main categories, low energy and high energy. Low energy trauma was the most common cause that lead to cervical spine fractures (n=169; 80.9%), compared to high energy trauma (n=40; 19.1%). CT scan and X-ray were the main imaging modalities utilized to detect cervical spine fractures. Whereas, MRI was only utilized in (n=51; 24.4%). Overall mortality rate was (n=17; 8.1%) at 30 days. Out of which (n=1; 5.9%) was in a patient who was surgically treated while the remaining (n=16; 94.1%) were in those treated conservatively. Conclusions Cervical spine injuries in older people are clinically important. Low energy trauma particularly falls, were the main mechanism of cervical spine injury. Upper cervical spine injuries, mainly C2, is the most common cervical spine fracture and were most commonly detected using CT scan. External immobilization was our treatment of choice for most of the cervical spine injuries in the older people. These patients are very similar with respect to mean age, mechanism of injury and 30 days mortality rate as hip fracture patients.