We investigated an ablation impulse irradiated by a nanosecond laser with an Al planar and sphere target in a large beam spot. A torsion pendulum was developed to investigate single pulsed laser ablation impulses. A beam spot size of about 1 mm diameter was selected as the large spot size because investigations have proved that a beam spot size less than 420 μm satisfied a one-dimensional plume expansion model. The results show that the minimum laser fluence corresponding to an observable ablation impulse of a planar target is about 3 J cm−2, and the optimum laser fluence corresponding to the highest impulse coupling coefficient is about 10 J cm−2 for both large and small beam spots. Our investigations prove that these two parameters are independent of the beam spot size. The impulse investigation of a sphere-shaped target reveals that its overall impulse is lower than that of a planar one irradiated by a large laser beam spot in high laser fluence regimes, especially when a strong plasma plume event is happening. This phenomenon may be caused by different plasma plume propagation directions due to a non-flat surface of the sphere targets because the plume expansion by nanosecond laser ablation is mainly normal to the local surface.
Rationale: Pediatric femoral shaft combined with ipsilateral femoral neck fractures are very rare but challenging injuries fraught with the development of avascular necrosis, coxa vara, and leg length discrepancy. Majority of the previous reports indicated the neck femur fracture was fixed with cannulated screws or/and pins, femoral shaft fracture was stabilized with a plate and screws. However, we used cannulated screws combined with elastic stable intramedullary nails to minimally invasive procedures treat this type of injury and achieved good follow-up results. Patient concerns: A 7-year-old boy (Case 1) was hospitalized due to a traffic accident resulting in swelling and deformity of the right thigh accompanied by limited mobility of hip and knee. A 5-year-old male child (Case 2) presented with pain and swelling in the bilateral lower limb after fall from approximately 12 feet. Diagnoses: Physical examination, X-ray film, and computed tomography were performed. Both patients were diagnosed with ipsilateral femoral neck and shaft fracture. Interventions: The fractures were reduced closed by image-intensifier imaging. Two partially threaded cancellous screws were used to fix femoral neck fracture, and elastic intramedullary nails were performed to stable the femoral shaft fracture. Postoperatively, the patients were immobilized in a one-and-a-half hip spica cast for six weeks. The internal fixations were removed after one year. Outcomes: Case one was follow-up at 14 months and the other one was followed up for 3 years. And at the last follow-up showed a normal and painless hip function. No clinical complications were found during follow-up visit, including head penetration, implant failure, fracture nonunion, avascular necrosis and hip varus deformity. Lessons: Clinician should carefully check and read relevant imaging data to avoid missed diagnosis. And the internal fixation method described in this paper may be more minimally invasive.
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