Management of complex and redo cases of pelvic fracture urethral injuries

Objectives:Pelvic fracture urethral injuries(PFUI)result from traumatic disruption of the urethra.A significant proportion of cases are complex rendering their management challenging.We described management strategies for eight different complex PFUI scenarios.Methods:Our centre is a tertiary referral centre for complex PFUI cases.We maintain a prospective database(1995e2016),which we retrospectively analysed.All patients with PFUI managed at our institute were included.Results:Over two decades 1062 cases of PFUI were managed at our institute(521 primary and 541 redo cases).Most redo cases were referred to us from other centres.Redo cases had up to five prior attempts at urethroplasty.We managed complex cases,which included bulbar ischemia,young boys and girls with PFUI,PFUI with double block,concomitant PFUI and iatrogenic anterior urethral strictures.Bulbar ischemia merits substitution urethroplasty,most commonly,using pedicled preputial tube.PFUI in young girls is usually associated with urethrovaginal fistula.Young boys with PFUI commonly have a long gap necessitating trans-abdominal approach.Our success rate with individualised management is 85.60%in primary cases,79.13%in redo cases and 82.40%in cases of bulbar ischemia.Conclusion:The definition of complex PFUI is ever expanding.The best chance of success is at the first attempt.Anastomotic urethroplasty for PFUI should be performed in experienced hands at high volume centres.

Molecular Dynamics Simulation of Tensile Deformation and Fracture of γ-TiAl with and without Surface Defects

Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The results indicate that brittle fracture occurs in perfect bulk; surfaces and edges will be detrimental to the strength of materials and provide dislocation nucleation site. The defects on surfaces and edges cause further weakening with various effects depending on defect type, size, position and orientation,while the edge dimples are the most influential. For γ-TiAl rods with surface dimples, dislocations nucleate from an edge of the rod when dimples are small, dimple dislocation nucleation occurs only when the dimples are larger than a strain rate dependent critical size. The dislocations nucleated upon [001]tension are super dislocations with Burger vectors 〈011] or 1/2 〈 112] containing four 1/6 〈 112 〉 partials. The effects of surface scratches are orientation and shape sensitive. Scratches parallel to the loading direction have little influence, while sharp ones perpendicular to the loading direction may cause crack and thus should be avoided. This simulation also shows that, any type of surface defect would lower strength,and cause crack in some cases. But some may facilitate dislocation nucleation and improve ductility of TiAl if well controlled.