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PubMed2002

Spinal injuries caused by the acceleration of ejection.

The speed and altitude at which modern military aircraft operate are such that escape can only be achieved by some means of forcibly propelling the aircrew clear of the aircraft. The most common method of doing this is by use of an ejection seat. The use of such seats, whilst generally life saving, exposes aircrew to forces that may be at the limits of human tolerance. Each phase of the ejection sequence is associated with characteristic injury patterns and of particular concern is the occurrence of spinal compression fractures, which are caused by the upward acceleration of the ejection seat. Thorough investigation of aircrew who eject is necessary and magnetic resonance imaging of the spines of these aircrew is now becoming mandatory. Aircrew who sustain stable anterior wedge compression fractures usually require no invasive treatment, but are prevented from flying aircraft fitted with ejection seats for 3-4 months.

Acceleration↗
PubMed1998

Measurement of whole-body human centers of gravity and moments of inertia.

With the inclusion of women in combat aircraft, the question of safe ejection seat operation has been raised. The potential expanded population of combat pilots would include both smaller and larger ejection seat occupants, which could significantly affect seat performance. The method developed to measure human whole-body CG and MOI used a scale, a knife edge balance, and an inverted torsional pendulum. Subjects' moments of inertia were measured along six different axes. The inertia tensor was calculated from these values, and principal moments of inertia were then derived. Thirty-eight antropometric measurements were also taken for each subject to provide a means for direct correlation of inertial properties to body dimensions and for modeling purposes. Data collected in this study has been used to validate whole-body mass properties predictions. In addition, data will be used to improve Air Force and Navy ejection seat trajectory models for the expanded population.

Adult↗
PubMed2002

Return to flight status following total hip replacement: a case report.

In the recent past, total hip replacement (THR) surgery in naval aviation personnel has been considered for selected individuals. There is a trend in the armed services to return individuals to flight status after total hip arthroplasty. Some individuals have successfully returned to ejection seat aircraft. A case report of an aviator who returned to tactical flying in the F/A-18 community is presented. This naval aviator has functioned successfully on a shipboard environment and accumulated in excess of 900 flight hours without functional compromise after successful hip arthroplasty, reporting no difficulty with aviation-related ergonomic issues, such as ingress/egress, sitting in a confined cockpit, or tolerating G forces. Two other individuals have also returned to flight status, but have not accumulated a significant number of flight hours to warrant evaluation. Irrespective of the apparent early success in returning to flight status, significant concerns remain. This preliminary assessment of individuals returned to flight status after THR appears to justify return to flight status, including ejection seat aircraft. However, there is a potential for hip fracture or dislocation in the event of ejection or PLF which poses significant risks for aircrews requesting return to flight status after THR. Additionally, personnel in this relatively young population should be advised of the likelihood of accelerated wear imposed by strenuous activity.

Adult↗
PubMed1996

Anthropometric measurements and ejection injuries.

BACKGROUND: A previous study examined anthropometric variables to determine possible ejection seat risk factors. It concluded that individuals who weighed below the average body weight or who met the criteria of having a tall, thin physique as measured by body mass index (BMI = kg.m-2) were significantly more at risk for acceleration induced back injuries. HYPOTHESIS: Because of the increased number of female pilots and the potential need to modify ejection seats for lighter aviators, this retrospective analysis of Naval Safety Center data attempted to reproduce and confirm the same results with more current data, covering a 5-yr period from Jan 1989-Dec 1993. METHODS: In this study, the same criteria were used to define back injury, including thoracic or lumbar vertebral fractures and soft tissue injuries, and the same anthropometric variables were used, including weight, height, BMI, and below average weight. Additional categories of injury were examined, including all spinal fractures alone without soft tissue back injuries, all injuries combined, and severity of injury. Sitting height and trunk height were added to the variables. RESULTS: Out of 810 aircrew involved in mishaps, 199 ejected. Of all the ejections, 111 (56%) had some type of injury as a result of the ejection. Severe injuries occurred in 8 (4%) including 4 (2%) fatalities. Back injuries occurred in 44 (22%), and 8 (4%) involved spinal fractures. Although there were no significant risk factors for ejection back injury, weight and height were statistically significant risk factors for severe injury and spinal fracture, respectively. CONCLUSIONS: Aircrew with severe injury were heavier (average weight 88 kg. vs. 79 kg.). In addition, taller aircrew (185 vs. 180 cm.) were at increased risk for any spinal fracture.

Acceleration↗
PubMed1997

Spontaneous resolution of a disc protrusion in a military aviator: a case report.

The case history of a 38-yr-old military aviator qualified on a range of rotary and fixed wing aircraft is presented. A radiologically evident and clinically debilitating (initially) lumbar disc protrusion was the source of the aviator's temporary grounding from flying duties. A full clinical recovery was made and he returned to flying, eventually to ejection seat aircraft. It is proposed that: 1.) wherever possible, initial conservative non-invasive management of back problems is preferable; 2.) lumbar disc lesions may sometimes totally spontaneously resolve (retraction or autolysis?), and; 3.) development and diagnosis of a lumbar disc lesion should not always be an automatic permanent expulsion from rotary wing or ejection seat aircraft.

Adult↗