Microstructure characterization of ZK60 magnesium alloys using TEM and HR-EBSD.

ZK60 (Mg-Zn-Zr) alloys exhibited a variation in precipitates with aging, and their mechanical properties also changed. Microindentation tests were carried out on two types of ZK60 alloys of solid solution (T4) and peak aging (T6). Microstructure and texture evolution during indentation was investigated using electron backscatter diffraction. Twinning occurred near the indentation marks in most grains. It was found that tensile twinning was dominant, and two twin variants were usually observed. Texture and microstructure evolution by twinning and slip activation was further examined by uniaxial compression test with strain. The initial random orientation gradually changed into basal fibers with strain. Some grains with nonbasal orientations aligned with the loading direction easily underwent twinning followed by slip deformation. Other grains near basal orientations revealed only slip deformation.

Does low-dose aspirin increase blood loss after spinal fusion surgery?

BACKGROUND CONTEXT: Low-dose aspirin for the prevention of cardiovascular disease is recommended to be discontinued at least 7 days before spinal surgery. PURPOSE: To determine the effect of stopping low-dose aspirin at least 7 days before surgery on the level of the perioperative blood loss or complications related to hemorrhage. STUDY DESIGN: Retrospective case study. PATIENT SAMPLE: Patients who underwent spinal fusion surgery for degenerative lumbar disease. OUTCOME MEASURE: Clinical outcome was measured by the Oswestry Disability Index. METHODS: The aspirin group included 38 patients who had taken 100 mg aspirin for an average of 40.3 months. They stopped aspirin for at least 7 days before surgery (mean, 9.0 days). The control group included 38 patients who had not taken aspirin. Both groups were matched in terms of age, gender, number of fused segments, and surgical procedures. The diagnosis in all patients was degenerative spinal disease. RESULTS: The mean age in the aspirin and control groups was 68.5 and 69.1 years, respectively. The mean number of levels fused was 2.0 segments in both groups. During surgery, the estimated blood loss was 855.3 cc in the aspirin group and 840.8 cc in the control group with no significant difference (p=.84). However, there was a significant difference in blood drainage after surgery. The hemovac blood drainage after surgery was 864.4 cc in the aspirin group but only 458.4 cc in the control group (p<.001). Therefore, the transfusion requirement after surgery was significantly greater in the aspirin group than in the control group (p=.03). The rate of complications related to hemorrhage was higher in the aspirin group than in the control group. CONCLUSIONS: The intraoperative blood loss during spinal fusion surgery was similar in both groups. However, the blood drainage after surgery was significantly higher in the aspirin group despite stopping aspirin 7 days before surgery. Hence, surgeons should pay careful attention to postoperative blood loss and complications related to hemorrhage in patients who have been taking low-dose aspirin.

Risk factors of sagittal decompensation after long posterior instrumentation and fusion for degenerative lumbar scoliosis.

STUDY DESIGN: A retrospective study of clinical results of operative treatment for degenerative lumbar scoliosis. OBJECTIVE: To determine the risk factors of sagittal decompensation after long instrumentation and fusion to L5 or S1. SUMMARY OF BACKGROUND DATA: Little is known about the risk factors for sagittal decompensation, which was defined in this study as sagittal C7 plumb falling anterior >8 cm from the posterosuperior corner of the sacrum. METHODS: Forty-five patients (mean age: 64.4 year) with adult degenerative lumbar scoliosis were reviewed retrospectively with a minimum 2 years. The mean number of levels fused was 6.1 +/- 1.6 segments. The upper instrumented vertebra ranged from T9 to L2. The lower instrumented vertebra was L5 and S1 in 24 and 21 patients, respectively. RESULTS: Sagittal decompensation (SD) developed in 19 patients. The most significant risk factors of SD were preoperative sagittal imbalance and high pelvic incidence. The preoperative sagittal C7 plumb was more positive (67.9 mm) in the decompensation group than in the balance group (37.0 mm) (P = 0.002). There was a significant difference in pelvic incidence between 61.7 degrees in the decompensation and 54.9 degrees in the balance group (P = 0.01). The preoperative lumbar lordosis was hypolordotic in the decompensation group, however, it was not found to be a risk factor. Pseudarthrosis was identified at the lumbosacral junction in 5 patients, and 4 of them (80%) had SD. SD developed in 55% of patients who had loosening of the distal screws and 50% of patients with hypolordotic lumbar fusion. Distal adjacent segment disease was more likely to cause SD than proximal adjacent segment disease. CONCLUSION: Sagittal decompensation is common after long posterior instrumentation and fusion for degenerative lumbar scoliosis. It is mostly associated with complications at the distal segments, including pseudarthrosis and implant failure at the lumbosacral junction. Restoration of optimal lumbar lordosis and secure lumbosacral fixation is necessary especially in patients with preoperative sagittal imbalance and high pelvic incidence in order to prevent sagittal decompensation after surgery.