Physical effects of ejection on the head-neck complex: demonstration of a cadaver model

Vertebral fracture is the most common severe injury during high-speed pilot ejection. However, the loading paradigm experienced by pilots may also lead to soft-tissue spinal injuries that are more difficult to quantify and can lead to long-term deficits. This manuscript describes a new experimental protocol to simulate the effects of pilot ejection on the tissues of the head-neck complex. The model permits precise control of head-neck complex initial positioning, detailed analysis of head and spinal kinematics and upper and lower neck loads, and the ability to thoroughly investigate and identify soft-tissue injuries through upper and lower neck injury criteria, radiography, manual palpation, and cryomicrotomy. For the current test, peak acceleration of +14.8 Gz was similar to actual ejection events and duration of the acceleration pulse was approximately 100 ms. The specimen was oriented in flexion prior to initiation of inferior-to-superiorly directed acceleration. Subfailure ligamentum flavum injuries were sustained at the C4-C5 and C5-C6 cervical spinal levels and identified by increased segmental motions during the simulated ejection, increased laxity following testing, and cryomicrotomy. Upper and lower neck injury criteria did not predict these soft-tissue injuries. This experimental model can be used for detailed analysis of the effects of gender, head-neck orientation, helmet instrumentation, and acceleration pulse characteristics on cervical spine injury potential during pilot ejection events.