INJURY RISK FOR RESEARCH SUBJECTS WITH SPINA-BIFIDA OCCULTA IN A REPEATED IMPACT STUDY - A CASE REVIEW

Spina bifida occulta (SBO) occurs in 18-34% of the normal U.S. populat ion. Recently, 16.5% of normal, asymptomatic male soldier volunteer ca ndidates in a U.S. Army Aeromedical Research Laboratory ride motion st udy were excluded from the study because they had SBO at one vertebral level. Disqualifying this percentage of screened research subject can didates threatened the timely completion of the schedule-intense proto col. Although one study suggests that SBO at spinal level S1 has a hig her incidence of posterior disc herniation, the preponderance of clini cal literature reports that spina bifida occulta is not a medical prob lem. The impact literature indicates that lumbosacral vertebral bodies fracture at 7.14 kN in static compression and 20+ G during dynamic ve rtical impacts. In this paper, we examined the human data observed in ejection seat incidents, the rationale for excluding volunteers with s ingle level SBO and the path of axial load transmission through the lu mboscral spine. Based on the findings, we concluded that research volu nteers with single level SBO are not at increased risk Tor injury and recommended inclusion of these volunteers in future studies involving repeated axial impacts due to ride motion.