Review: Geometric interpretation of reflection and transmission RHEED patterns.

Reflection high-energy electron diffraction (RHEED) is widely used to characterize the surface structure of single crystals. Moreover, RHEED has become a standard tool to monitor thin film growth in molecular beam epitaxy and is used to monitor other vapor deposition techniques including evaporation, sputtering, and pulsed laser deposition. With the rapid development of the fabrication methods and use of nanoparticles, RHEED operating in the transmission mode is being applied to characterize nanoparticles on surfaces. In this review, the fundamentals needed to interpret RHEED patterns from the top few atomic layers, in its reflection mode, and from nanoparticles and nanofeatures, in its transmission mode, are discussed based on the geometric kinematic approximation. Examples are provided on the interpretation of RHEED patterns from unreconstructed and 2 × 1-reconstructed Si(100), InP(100), highly oriented pyrolytic graphite, indium nanoparticles, and indium growth on Si(100)- 2 × 1.

Biomechanical evaluation of occipitocervicothoracic fusion: impact of partial or sequential fixation.

BACKGROUND CONTEXT: Surgical instrumentation used for posterior craniocervical instability has evolved from simple wiring techniques to sophisticated implant systems that incorporate multiple means of rigid fixation for the cervical spine. Polyaxial screws and lamina hooks in conjunction with occipital plating and transitional rods for caudal fixation theoretically allow for fixation points at each vertebra along the posterior aspect of the cervical spine. However, the potential for anatomical constraints to prevent intraoperative instrumentation at the desired vertebral level exists. The biomechanical implications of such "skipped segments" have not been well documented. PURPOSE: The purpose of this study was to determine the biomechanical effects of partial three-point fixation versus sequential fixation at all levels of the cervical spine from the occiput to T1. STUDY DESIGN/SETTING: Fresh frozen human cadaveric cervical spines from the occiput (CO) to T1 were prepared and mounted on a spine simulator. Motion was assessed by a three-dimensional optoelectronic motion measurement system. Kinematic data were collected and range of motion (ROM) was analyzed and reported. METHODS: Eight human noninstrumented intact spines (Treatment 1) were tested for baseline ROM which was subclassified into axial (CO-C2), upper subaxial (C2-C4), lower subaxial (C4-T1), and total (CO-T1) ROM. Flexion extension, lateral bending, and axial torsion testing with an applied +/-3Nm moment was conducted. The same testing protocol was performed after three-point fixation in which screws were placed at the CO, C4, and T1 (Treatment 2), and also after sequential fixation at all levels from CO through T1 (Treatment 3). Fixation was achieved using an occipital plate, 12-mm lateral mass screws for C3 through C6, and 20-mm lateral mass or pedicle screws were used for C1, C2, C7, and T1. RESULTS: Intact spine testing (Treatment 1) showed statistically significant larger ROM for all segments and for overall ROM when compared with both Treatment 2 (partial fixation CO, C4, and T1) and Treatment 3 (sequential fixation at all levels from the occiput to T1). When comparing Treatment 2 with Treatment 3, no significant difference in flexion extension ROM was detected between axial, upper subaxial, lower subaxial, and total overall ROM (p > .05). Lateral bending showed statistically significant increased ROM for Treatment 2 constructs compared with Treatment 3 constructs in total overall lateral bend ROM. For axial rotation, there was significantly increased ROM for Treatment 2 at the lower subaxial segment and total overall ROM (p < .05) when compared with Treatment 3. CONCLUSIONS: There was no statistical difference between the three-point fixation treatment group and the sequential fixation group in flexion extension bending. Lateral bending and axial rotation demonstrated an increase in total overall ROM with partial fixation compared with fixation at all levels. Axial rotation in particular showed increased mobility in the lower cervical spine for the partial fixation group. In the instance where surgeons are not able to apply sequential fixation at diseased levels, especially for the lower subaxial cervical spine, particular attention to limitation of lateral bending and axial rotation by the use of external orthotics must be considered.

Pediatric craniopharyngioma--rationale for multimodal management: the Egyptian experience.

BACKGROUND: Situated in a suprasellar location, craniopharyngiomas produce devastating endocrinological manifestations, visual impairment, and raised intracranial pressure, presenting a formidable disease entity for the neurosurgeon as well as the 'craniopharyngioma team'. OBJECTIVE: To evaluate direct postoperative and long-term results based on the extent of surgical removal and administration of radiotherapy. PATIENTS AND METHODS: Sixty-two new cases of pediatric craniopharyngioma were divided into three groups according to extent of removal: A (complete), B (subtotal), and C (partial). Groups A and B receiving primary postoperative radiotherapy were tagged groups Ar and Br. RESULTS: Group A had significantly less recurrence rate than group B (p < 0.005); however, direct postoperative morbidity and mortality were worse (p < 0.05). Group C fared worse than the other two groups. In groups A and B with recurrence and in groups Ar and Br, radiotherapy provided long-term control. CONCLUSION: The aim at first surgery should be total removal. Subtotal removal is warranted for more resilient tumors, while partial removal should be avoided as it provides poor results. Adjuvant radiotherapy is a useful tool in providing long-term tumor control.

Prevalence of neuropathic pain among patients suffering from chronic low back pain in Saudi Arabia.

OBJECTIVE: The aim of this study was to assess the prevalence of neuropathic pain among patients suffering from chronic low back pain using the Leeds assessment of neuropathic symptoms and signs (LANSS) pain scale. METHODS: This was a pilot study collected from 10 centers in the Middle East Region, with each center enrolling 10 patients between November 2004 and January 2004. In total, 100 patients with chronic low back pain were included in the study. The LANSS clinical assessment score was used to assess the presence of neuropathic pain. Patients with score >12 were considered to have neuropathic pain, while patients with score a < 12 were considered as having nociceptive pain. RESULTS: We found that 41% of the chronic low back pain patients had neuropathic pain and 59% had nociceptive pain. CONCLUSION: The ability to identify neuropathic pain mechanisms should lead to individualized treatment resulting in improved pain control in this group of patients with chronic low back pain.

Prevalence of neuropathic pain among patients suffering from chronic low back pain in Saudi Arabia.

OBJECTIVE: The aim of this study was to assess the prevalence of neuropathic pain among patients suffering from chronic low back pain using the Leeds assessment of neuropathic symptoms and signs (LANSS) pain scale. METHODS: This was a pilot study collected from 10 centers in the Middle East Region, with each center enrolling 10 patients between November 2004 and January 2004. In total, 100 patients with chronic low back pain were included in the study. The LANSS clinical assessment score was used to assess the presence of neuropathic pain. Patients with score > or =12 were considered to have neuropathic pain, while patients with score a less than 12 were considered as having nociceptive pain. RESULTS: We found that 41% of the chronic low back pain patients had neuropathic pain and 59% had nociceptive pain. CONCLUSION: The ability to identify neuropathic pain mechanisms should lead to individualized treatment resulting in improved pain control in this group of patients with chronic low back pain.

Traumatic injuries of the distal femoral physis. Retrospective study on 151 cases.

This is a retrospective study on a series of 151 injuries involving the distal femoral physis. The average age at the time of injury was 12.3 years. Patients were followed for an average of 8.2 years. The complications encountered were not insignificant and the satisfactory results were relatively low (64.9%). The juvenile age group was the most affected with complications. Salter-Harris type II injuries predominated (43.0%) and they did not have a good prognosis as previously suggested. Symptomatic knee ligamentous laxity was found in 12 patients (7.9%). Compartment syndrome is a devastating complication that occurred in 2 cases (1.3%). We stress the point that a child with a physeal injury of the distal femur should be followed for several years after injury and preferably until skeletal maturity. The surgeon must have high index of suspicious for compartment syndrome. Physeal injuries of the distal femur and in particular Salter and Harris type II should be reduced anatomically and fixed well. Whether this should be achieved by closed or opened means, requires a controlled prospective study to provide a confident answer.