The ascending thoracic aorta is poorly understood mechanically, especially its risk of dissection. To make better predictions of dissection risk, more information about the multidimensional failure behavior of the tissue is needed, and this information must be incorporated into an appropriate theoretical/computational model. Toward the creation of such a model, uniaxial, equibiaxial, peel, and shear lap tests were performed on healthy porcine ascending aorta samples. Uniaxial and equibiaxial tests showed anisotropy with greater stiffness and strength in the circumferential direction. Shear lap tests showed catastrophic failure at shear stresses (150-200 kPa) much lower than uniaxial tests (750-2500 kPa), consistent with the low peel tension ($60 mN/mm). A novel multiscale computational model, including both prefailure and failure mechanics of the aorta, was developed. The microstructural part of the model included contributions from a collagenreinforced elastin sheet and interlamellar connections representing fibrillin and smooth muscle. Components were represented as nonlinear fibers that failed at a critical stretch. Multiscale simulations of the different experiments were performed, and the model, appropriately specified, agreed well with all experimental data, representing a uniquely complete structure-based description of aorta mechanics. In addition, our experiments and model demonstrate the very low strength of the aorta in radial shear, suggesting an important possible mechanism for aortic dissection.

Ascending thoracic aortic aneurysms (ATAA) have a high propensity for dissection, which occurs when the hemodynamic load exceeds the mechanical strength of the aortic media. Despite our recognition of this essential fact, the complex architecture of the media has made a predictive model of medial failure-even in the relatively simple case of the healthy vessel-difficult to achieve. As a first step towards a general model of ATAA failure, we characterized the mechanical behavior of healthy ascending thoracic aorta (ATA) media using uniaxial stretch-to-failure in both circumferential (n ¼ 11) and axial (n ¼ 11) orientations and equibiaxial extensions (n ¼ 9). Both experiments demonstrated anisotropy, with higher tensile strength in the circumferential direction (2510 6 439.3 kPa) compared to the axial direction (750 6 102.6 kPa) for the uniaxial tests, and a ratio of 1.44 between the peak circumferential and axial loads in equibiaxial extension. Uniaxial tests for both orientations showed macroscopic tissue failure at a stretch of 1.9. A multiscale computational model, consisting of a realistically aligned interconnected fiber network in parallel with a neo-Hookean solid, was used to describe the data; failure was modeled at the fiber level, with an individual fiber failing when stretched beyond a critical threshold. The best-fit model results were within the 95% confidence intervals for uniaxial and biaxial experiments, including both prefailure and failure, and were consistent with properties of the components of the ATA media.

INTRODUCTIONThe stability of the trochanteric fracture depends on the amount of contact between the proximal and distal main fragments. Trochanteric fractures with comminution of posteromedial buttress exceeding simple lesser trochanteric fragment or with subtrochanteric extension are termed as unstable. In 3-part fractures stability is inversely proportional to the size of the lesser trochanteric fragment. Instability occurs when more than 50% of the calcar is affected allowing the proximal fragment to collapse into varus with shortening. Reverse obliquity fracture is unstable fracture in which major fracture line extends outward and downward from the lesser trochanter.Unstable trochanteric fractures are technically much more challenging than stable fractures. Stable reduction of an intertrochanteric fracture requires providing medial and posterior cortical contact between the major proximal and distal fragment to resist varus and posterior displacing forces. For unstable fractures intramedullary implants are (biomechanically) superior.1 Lag screw cut-out failure following fixation of unstable intertrochanteric fractures in osteoporotic bone remains an unsolved challenge. 2 ABSTRACTBackground: Treatment of unstable trochanteric fracture is much more challenging than stable fracture. These fractures require stable fixation to minimize the fracture and implant related complications. Need of this study is to assess the suitable implant for stable fixation of unstable trochanteric fracture with less intra and postoperative complications and good functional outcome. Methods: In this prospective randomized comparative study, 64 patients were distributed into two groups. Group A consisted of patients treated by proximal femoral nail (PFN) (n=32) and group B treated by dynamic hip screw (DHS) (n=32). All the patients were evaluated preoperatively and surgery was done according to the group they were allotted. Post-operative follow up was done at 6 weeks, 3, 6 and 12 months. Results: Average age of the patients in this study was 51.26±10.24 year. In this study patients were followed up for an average of 10.87±2.61 month. The duration of surgery was shorter in PFN group. Weight bearing was earlier in PFN group than DHS group. Mean functional ability score was better in PFN group with significant gain in function earlier as compared to DHS group. Conclusions: PFN is a better implant for internal fixation of unstable trochanteric fractures which allows early mobilization and has got better functional outcome score in early postoperative period than DHS.

Ascending thoracic aortic aneurysm (aTAA) is a pathological condition with a high risk of dissection and rupture. Clinically, management of aTAA balances the risk of rupture with that of surgery-related complications. The risk of aneurysm rupture is known to correlate with aneurysm diameter. 1,2 Aneurysms greater than 6 cm in diameter have a significantly higher risk of rupture. 1 Current guidelines for intervention suggest surgical intervention for aTAA diameters greater than 5.5cm for patients without connective tissue disorders. 1

Background: Fractures around hip is an increasing burden in elderly causing significant morbidity and mortality. Periprosthetic fractures occurring after hemiarthroplasty of hip is a serious complication. In this study, we have reviewed our experience in the treatment of periprosthetic fractures. Method: In our study 8 patients (6 men and 2 women; mean age: 65 ± 8 years) with periprosthetic fractures treated with ORIF with trochanteric hook plate with proximal unicortical screws in the zone of prosthesis and below by bicortical screws with a minimum follow up of 4months and maximum up to 1year was carried out. The average union period was checked after operation with radiologic findings. Radiologic outcomes were evaluated .All cases were assessed postoperatively for functional outcome in terms of range of motion, pain and walking distance. Results: The average time for union was 16 weeks and we have achieved 90% of union and Good range of motion with no pain. There was no case with loss of fixation or loss of reduction requiring revision surgery. Conclusion:We observed good functional outcome in patient treated with Trochanteric hook plate. Reversed trochanteric hook plate is a reliable, effective option for management of Vancouver type B2 periprosthetic femoral fractures.