G.H. Choi

Comparison of Al-Cu-Fe quasicrystalline particle reinforced Al composites fabricated by conventional casting and extrusion

Aluminum matrix composites reinforced by Al62Cu26Fe12 gas atomized powders were produced by conventional metallurgical processes, such as gravity casting with stirring and hot extrusion. This investigation was mainly focused on the dependency of the yield stress at room temperature as a function of the volume fraction of reinforcement, but other variables such as the matrix, coating layer around the particles, and processing were also investigated. For as-extruded composites, the addition of the Al-Cu-Fe particles improved the yield stress, although not dramatically owing to the large particle size. In contrast, it was found that the yield stress was considerably enhanced for the as-cast composites up to 10%(AlCuFe)p, while an asymptotic value was observed afterward. The dominant parameter appeared to be the strength of the matrix, which was found to be proportional to the volume fraction of the reinforcement. These results are discussed in relation with the possible strengthening mechanisms in order to estimate the role of the icosahedral and related crystalline phases on the increase of yield stress.

Intraoperative indocyanine green video-angiography: spinal dural arteriovenous fistula.

Study Design. Technical note. Objective. To describe the use of intraoperative indocyanine green (ICG) video-angiography for obliteration of a spinal dural arteriovenous fistula (DAVF) and to show a video clip. Summary of Background Data. ICG video-angiography is an emerging tool for delineating intraoperative vascular anatomy, and it has a significant potential in the treatment of vascular diseases in the spine. Methods. The authors presented a case of a 73-year-old man with progressive and debilitating bilateral lower extremity weakness. The patient was diagnosed with a spinal DAVF of 10th thoracic spine based on the results of conventional spinal angiography. Results. The patient underwent T9–10 laminotomy for microsurgical clip occlusion. Intraoperative ICG video-angiography was used before clip placement to identify the arterialized veins of the fistula and after clip placement to confirm obliteration of the fistulous connection and restoration of normal blood flow. Conclusion. Intraoperative ICG video-angiography serves an important role in the microsurgical treatment of DAVF. It is simple and provides real-time information about the precise location of spinal DAVF and result after obliteration of spinal DAVF.

Stand-alone cervical cages versus anterior cervical plate in 2-level cervical anterior interbody fusion patients: clinical outcomes and radiologic changes.

Study Design: Retrospective study. Objectives: To compare the efficacy of 2-level anterior cervical discectomy and fusion with cage alone (ACDF-CA) and with cage and plate construct (ACDF-CPC) with regard to clinical outcome and radiologic changes. Summary of Background Data: The use of stand-alone cervical interbody cages in ACDF has become popular, but high subsidence rates have been reported in the literature. Methods: A total of 54 consecutive patients who underwent 2-level ACDF-CA or ACDF-CPC after suffering from cervical radiculopathy were divided into 2 groups: group A (n=28) underwent ACDF-CA, group B (n=26) underwent ACDF-CPC. Fusion rate, global and segmental kyphosis, disk height, and subsidence rate were assessed by radiolographs. Clinical outcomes were assessed using Robinson’s criteria. Results: Solid fusion was achieved in 96.43% (27/28) in group A and in 96.15% (25/26) in group B. Fusion segmental kyphosis of >5 degrees occurred in 14.29% (4/28) of group A and in 7.69% (2/26) of group B; however, there was no statistical difference between the 2 groups (P>0.05). Subsidence occurred in 35.71% (10/28) of group A as compared with 11.54% (3/26) of group B (P<0.05). Clinical outcomes were similar in the 2 treatment groups. Conclusions: The use of cage and plate construct in 2-level ACDF results in a shorter fusion duration and a lower subsidence rate than that of cage alone; however, there is no significant difference in the postoperative global and segmental alignment and clinical outcomes between groups.

Effects of Lumbar Arthrodesis on Adjacent Segments Differences Between Surgical Techniques

Study Design. A finite element analysis. Objective. To evaluate the differences between surgical techniques in terms of the effects of arthrodesis on adjacent segments. Summary of Background Data. Augmentation with posterior rigid fixation combined with transpedicular screw insertion, which is one of the most popular techniques for lumbar arthrodesis, shows benefits in immediate stabilization and a higher fusion rate but is reportedly correlated with greater stress on adjacent segments. However, the increased stress on adjacent segments needs further evaluation because the differences of the effects on adjacent segments between surgical techniques, including anterior lumbar interbody fusion, posterior lumbar interbody fusion, and semirigid fixation, have not yet been determined. Methods. A finite element model of the human lumbar spine was developed. Three spinal segments (L2–L5) were used to investigate. The intact spinal model was validated by comparing it with previously reported models. Then, 4 arthrodesis models were analyzed and compared: (1) anterior lumbar interbody fusion model; (2) posterior lumbar interbody fusion model; (3) semirigid fixation model combined with posterior lumbar interbody fusion; and (4) rigid fixation model combined with posterior lumbar interbody fusion. Results. Among these 4 models, the rigid fixation model showed the greatest amount of stress, with increased intervertebral disc pressure and contact force of the facet joints of both upper and lower adjacent segments. The second highest stress levels were seen in the semirigid fixation model and the lowest stress levels were seen in the anterior lumbar interbody fusion model. Conclusion. Although bony fusion had been completed, the effects of lumbar arthrodesis on adjacent segments could vary according to the surgical technique used for arthrodesis. Semirigid fixation combined with arthrodesis deserves careful consideration and further detailed study because it may cause less stress on adjacent segments than rigid fixation while maintaining the benefits of the latter procedure.

Radiofrequency ablation of spine: an experimental study in an ex vivo bovine and in vivo swine model for feasibility in spine tumor.

Study Design. An experimental study of radiofrequency ablation (RFA) of spine in an ex vivo bovine and in vivo swine animal model. Objective. To study the feasibility of RFA for spine tumors close to the spinal cord, to examine the safety and efficacy of RFA, and to suggest quantitative guidelines for clinical application. Summary of Background Data. RFA has received increased attention as an effective and minimally invasive method for treating soft tissue tumors. However, there is currently only anecdotal evidence to support RFA of spinal tumors and only a few experimental studies have been conducted. Methods. We performed ex vivo experiments by producing 10 RFA zones in extracted bovine spines and an in vivo study by producing 8 RFA zones in a swine spine using internally cooled electrodes. The volume and diameter of ablation zones were evaluated and analyzed by the corresponding energy and ablation times. Results. In the ex vivo study, the average diameters of the ablation zones were 3.05 cm, 1.85 cm, and 1.26 cm, for the D1, D2, and D3 zones, respectively, and the average ablation volume was 4.19 cm3. In the in vivo study, the average diameters were 2.51 cm, 2.05 cm, and 1.28 cm, respectively, and the ablation volume was 6.80 cm3. The ablation zones demonstrated a positive correlation with ablation time, but the coefficients were 0.942 ex vivo and 0.257 in vivo. The temperature in the ex vivo study was inversely proportional to distance, with a maximal temperature of 63.7°C at 10 mm; however, the maximum temperature was 38.2°C in the in vivo study. Conclusion. This study demonstrated that sufficient RFA zone volume could be induced, which suggests that RFA is feasible and safe for application to human spinal tumors with predictability. Level of Evidence: N/A