Biomechanical evaluation of Caspar cervical screws: comparative stability under cyclical loading.

Anterior cervical instrumentation is used as an adjunct to bone fusion; however, definitive biomechanical data to support some applications and techniques are lacking. In the absence of supportive experimental data, posterior cortical penetration has been recommended with the Caspar system. Previously, we compared the axial pull-out strength of Caspar screws with and without posterior cortical penetration. This study compares the stability of unicortical versus bicortical screw penetration groups under cyclical loading simulating physiological flexion-extension. Caspar screws were placed in human cadaveric vertebrae with or without posterior cortical purchase. Each screw was separately tested, simulating flexion-extension to 200 cycles. Deformation time data allowed a direct comparison of screw "wobble" with and without posterior cortical purchase. The mean deformation differences between subcortical and bicortical groups were statistically significant and increased over time within both groups. Enhanced stability was noted with bicortical purchase throughout most of the examined range, becoming more pronounced over longer periods of cyclical loading. Significant (P < 0.05) increases in deformation over time were noted for both groups, suggesting potentially significant deterioration at the screw-bone interface, despite bicortical purchase. Such deterioration with repeated flexion-extension loading may be of concern in the use of Caspar plates in the presence of multicolumn instability.

Clinical and laboratory diagnosis of respiratory syncytial virus infection.

Infection with RSV is one of the most common respiratory viral infections in childhood, particularly in infants under 1 year of age. The disease is characterized by epidemic proportions of infection which occur regularly in all parts of the world in the winter months. The spectrum of the clinical disease is quite variable, and the infection may present as bronchiolitis, pneumonia, croup, or exacerbation of pre-existing reactive airway disease. Recent evidence has suggested that RSV infection may be frequently associated with apnea in infancy and possibly sudden-infant-death syndrome. Although the laboratory diagnosis of this infection can be successfully accomplished by any well-known and conventional procedures, such as tissue culture infectivity and determination of serologic response, recently it has become possible to diagnose the infection very rapidly by application of such techiques as immunofluorescent staining and enzyme-linked immunonoabsorbent assay (ELISA).

Viral vaccination via the mucosal routes.

Viral vaccines have been successfully administered by the mucosal route for two decades now. However, only in the last 10 years have the concepts involved in mucosal immunocompetence been well characterized. It is apparent that the bronchus-associated lymphoid tissue, the gut-associated lymphoid tissue, and the immunocompetent cells present in ocular tissue, conjunctiva, nasopharynx, genital tract, and secretions of the mammary glands represent the components of the common mucosal immune system. The predominant immunologic activity in the external mucosal surfaces is associated with secretory IgA and T lymphocytes, with variable contributions from other immunoglobulins and macrophages. Evidence presented in this review suggests that immunization via the mucosal routes of the respiratory and gastrointestinal tracts is the most effective means of inducing effective immunity in the mucosal surfaces as well as in the systemic tissues. Available experience with mucosal immunization with poliovirus, rubella virus, measles virus, and adenovirus vaccines in humans and with other viral vaccines in animals is briefly reviewed.

Cell-mediated immune responsiveness to measles. Its occurrence as a result of naturally acquired or vaccine-induced infection and in infants of immune mothers.

Studies of cell-mediated immunity (CMI) to measles were carried out in patients with natural measles infection, in recipients of live measles vaccine, and in umbilical cord blood specimens from infants of mothers who were seropositive for measles. Evidence of CMI to measles was found in 100% of patients with natural infection but in only 62% of vaccine recipients and, interestingly, in 40% of umbilical cord blood specimens. Eight of these infants were subsequently studied at 4 to 5 months of age, at which time evidence of measles CMI was still detectable in three. Sufficient stimulation of cell-mediated immune mechanisms may be a prerequisite for the development of life-long immunity to measles. The effect of congenitally acquired CMI to measles on the outcome of immunization or of exposure to natural measles during the first year of life remains to be determined.