CSRS – 2014

Please click on the “Disclosure” link for author/participant financial disclosure information.

E-Poster #41

Contiguous Spinal Instability Due to Tri-Phasic Kinematics from Underbody Blast Loading

Narayan Yoganandan, PhD, Milwaukee, Wisconsin John R. Humm, MS, Milwaukee, Wisconsin Frank A. Pintar, PhD, Milwaukee, Wisconsin Michael Mumert, MD, Milwaukee, Wisconsin Dennis J. Maiman, MD, PhD, Milwaukee, Wisconsin

Introduction: Inferior-to-superior loading of cervical spine coupled with/without helmet contact with roof/interior structure of vehicle is a postulated injury mechanism from underbody blasts from IEDs. Using a custom vertical accelerator device, this study applied simulated underbody blast loads to human cadaver head-neck complexes to determine forces, kinematics, injuries, injury mechanisms and instability at contiguous levels.

Methods: Pretest BMD, X rays and CT of six head-T2 complexes were obtained. Disc and facet joints were graded (two surgeons). Specimens were prepared with retro-reflective targets at various levels. T2-T3 was fixed. C7-T1 joint was unconstrained. A six-axis load cell was attached at inferior end. An appropriate-size military-combat-helmet was used for each specimen, determined based on individual head size. Prepositioning: T1 was inferiorly oriented at 30-degrees from horizontal. Occipital condyles were anterior to cervico-thoracic disc (seven-degrees forward of vertical axis). These were based on mean position data from a study of military volunteers. Tests were conducted using a vertical accelerator capable of imparting high-acceleration, short-duration pulses to specimen’s inferior end (Figure 1). Accelerometers, angular velocity and acoustic sensors, and strain gages were used on vertebrae. Tests were done at different velocities, applied sequentially such that low velocity initial baseline test was repeated in between two higher velocity tests. Roof structure of military vehicles was simulated at a distance of 0.13 m from top of helmet. Load cells recorded roof impact forces. High-speed videos were taken (5000 frames/second). X-rays and palpations were done in between tests. X-rays and CT were obtained following final test. Detailed dissection was performed.

Results: Age, stature, BMI: 55±9 years, 183±5 cm, 21±3 kg/m2. Impact pulses were within 10-millisecond rise-time. Kinematics, force and acceleration analysis demonstrated tri-phasic response: initial acceleration/compression wave transmitted from T2 to occipital condyles during launching phase, followed by extension kinematics of the column, and in final phase, additional (re)compression occurred from roof contact. Entire tri-phasic event occurred within 120-milliseconds. Forces during initial compressive wave transmission phase were similar in all specimens, while during final compression phase, roof-contacted specimens sustained significantly greater forces than non-contacted specimens (Figure 2). Injuries were consistent with vertical inferior to superior loading mechanisms, forces, moments and accelerations: vertebra fractures, anterior intrevertebral annulus disruptions and ligament tears, and facet injuries.

Conclusion: Tri-phasic response and inferior-to-superior loading is unique to military environments. Anterior, middle and posterior column injuries occurred in the third phase with helmet-head to roof contact associated with ‘buckling’ of cervical column, only possible through the local realign upward wave phenomenon to the entire fractured vertebra(e) cross section. Involvement of anterior column, disc and ligament injuries suggests: soft tissue-related injuries occur due to local segmental extensions during second phase of wave transmission. Roof contact during third phase of the response injured spine, leading to clinical instability at contiguous levels. These mechanistic features distinctly differ from neck injuries under civilian environments. Military neck injuries from underbody blast loads are unique, have complex tri-phasic phenomenon and involve additional contiguous segmental instability.

CSRS – 2014

Please click on the “Disclosure” link for author/participant financial disclosure information.

E-Poster #41 (continued)

Contiguous Spinal Instability Due to Tri-Phasic Kinematics from Underbody Blast Loading

Contiguous Spinal Instability: Tri-phasic Kinematics from Underbody Blast Loading

Narayan Yoganandan, PhD John R. Humm, MS Frank Pintar, PhD Michael Mumert, MD Dennis Maiman, MD, PhD Department of Neurosurgery Medical College of Wisconsin Milwaukee, WI 53226

Disclosure: This research was supported in part by the United States Army Cooperative Agreement W81XWH-12-2-0041, the Medical College of Wisconsin, and the Department of Veterans Affairs Medical Research. The views expressed are those of the authors and do not reflect official policy or position of the Department of the Army, Department of Defense or the United States Government.

Hypothesis and Objectives Hypothesis: Cervical spine injuries from underbody blast loading occurs from inferior-to-superior loading, with head contact with the interior structure of military vehicle Objective: Use custom vertical accelerator and apply simulated underbody blast loading to human cadaver head-neck complexes and determine cervical spine responses and document injuries

Methods • Use six human cadaver head-T2 specimens • Obtain Pretest BMD, X rays and CT scans • Grade discs and facet joints of the spine • Attach a six-axis load cell below T1 joint • Prepare with retro-reflective targets • Allow physiologic motions at C7-T1 • Attach a military combat helmet • Pre-position: use military volunteer data Orient T1 inferiorly at 300 from horizontal Occipital condyles anterior to C7-T1

Methods – continued • Tests done at different impacting velocities: applied sequentially : low velocity baseline test

repeated in between two higher velocity tests • With and without simulated roof structure: at 130 cm from the crown of the helmet

• Load cells recorded roof impact forces • High-speed videos obtained at 5000 f/s • X-rays and palpations done in between tests • X-rays and CTs obtained after the final impact test • Detailed dissection done for documenting injuries

Demographics

ID Sex Age years

Stature cm

Weight kg

BMI kg/m2

1 M 44 173 68 23 2 M 43 185 70 21 3 M 58 183 68 20 4 M 64 183 68 20 5 M 62 188 72 20 6 M 61 188 77 22

Mean: age: 55±9 years, , stature: 183±5 cm, BMI: 21±3 kg/m2

Results – Tri-Phasic Response

• Initial acceleration/compression wave transmitted from T2 to Occipital condyle during the launching phase

• This was followed by extension kinematics of the column • Final phase, (re)compression occurred from roof contact • Entire tri-phasic event occurred within 120-milliseconds • Forces similar in initial compression transmission phase • During final compression phase, roof-contact resulted in

greater forces than non-contacted specimens (next page)

Tri-Phasic Response – 3 m/s tests

Primary compression, phase 1

Re-compression, phase 3

Extension, phase 2

Summary: Peak Forces and Times

ID Phase 1 Phase 2 Phase 3

Force (N) Time (ms) Force (N) Time (ms) Force (N) Time (ms)

1 -2311 2.7 782 52.0 -1305 88.5 2 -2352 10.6 803 51.0 -907 86.9 3 -2270 13.1 566 50.4 -1095 87.2 4 -2856 15.1 849 41.0 -1811 72.2 5 -2930 11.4 393 47.1 -1326 76.5 6 -3080 8.3 1076 37.6 -2404 61.8

Specimens shown in green sustained no injuries, while Others sustained injuries -: refers to compressive force, +: refers to distractive force phase 1 phase 3

phase 2

Summary of Injuries

Summary • Inferior to superior loading of head-neck complex • Simulating underbody blast loading environments • Custom vertical accelerator for dynamic loading • Specimens had army combat military helmets • Recorded cervical-thoracic junction forces • Tests were done with and without roof • Tri-phase behavior of cervical spine: Compression from T1 – primary phase Extension loading – secondary transient phase Re-compression: head to roof contact – third phase

• Upper and lower cervical injuries