TECHNOLOGY AREAS: Biomedical, Human Systems

ACQUISITION PROGRAM: PMA202, Aircrew Systems, Non ACAT

OBJECTIVE: Develop computational models to understand and analyze acute and chronic back pain for combat air vehicle pilots and occupants taking into consideration the interaction between seating systems and posture and the generation of spinal pain.

DESCRIPTION: Pilots and crew of combat air vehicles, including fixed-wing attack, fighter and rotary-wing aircraft, can be exposed to inertial and task position stressors that generate pain. Repeated painful exposures with or without tissue damage are precursors to pain sensitization and chronic pain. Chronic pain leads to reduced operational readiness and long term medical treatment. A means of protection is needed to minimize the development of chronic back pain while maintaining short duration, high onset acceleration protection afforded by ejection and crashworthy seating. Equally important, though less well understood, is the contribution of long duration, static/quasi-static loading to chronic pain development. Current seating systems were designed to be a 'one-size-fits-all' with minimal adjustability and were intended for short and moderate duration exposures. Aircraft seating systems encompass a range of seat back angles from 0 degrees (vertical) to 17 degrees pitched back and seat pan angles from 0 degrees (horizontal) to 12 degrees pitched up. Seated postures vary ranging from long periods holding the same position while visually scanning the area or instruments through turning to look over their shoulders ("check six" position). All the while, they are restrained in their seats for missions as long as 12 hours and must be able to reach switches and controls overhead, behind, to the side and in front of them.

An optimal protective approach would take into account variability of operator anthropometry; the physical, inertial loading exposures of air combat vehicles; the task posture of the operator; the relevant specific low back/spinal anatomy; and the mechanisms of pain associated with back pain. There is a strong need to be able to analyze and quantify the influence of various mechanical stressors on pilot injury potential and to develop novel designs of occupant seating and restraint systems that reduce the spinal injury and chronic pain risk to all aircrew sizes during routine and catastrophic events. Computational models and parametric simulations are required to determine potential contributors to acute and chronic operator back pain and the specific pain mechanisms involved. Given the challenge of relating mechanical stresses to associated pain, a neurologist experienced working with pain patients should be included on the proposed team as a consultant. The computational models should be structured such that recommendations can be made towards improvements to seating, helmet and restraint systems, postures and operational guidelines. The models should also be able to determine the predicted design(s) efficacy.

PHASE I: Determine the feasibility of using human biomechanical models to expose a simulated occupant to the inertial and positional stressors, simulating the effect on the spine and onset of pain and predicting the spinal sensitization and pain time course.

PHASE II: Develop a human biomechanical model accounting for anthropometric variation of military population (5th to 95th percentiles), including gender related factors. This will include models of seating (geometry and cushions), restraints, cockpit geometry, and protective clothing / equipment. Validate the combined model against published data, including but not limited to the references listed below. Use the model to analyze existing operational procedures and propose improved operational guidelines.

PHASE III: Using guidelines developed in Phase II, develop prototype of the most promising protective concept that provide adaptive seating, comfort and adjustability for the maximum range of anthropometric sizes and conduct experimental testing and evaluation. Conduct operational unit evaluation of the prototype protective concept and implement necessary design changes. Re-evaluate the predicted performance based on implemented changes and revise protective concept based on results of evaluation until desired optimum protection is achieved.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: In addition to operators of land and sea combat vehicles, operator low back pain is a problem in the commercial transportation field. Such a protective capability would be valuable in mitigating the developing of pain and chronic back pain for operators of commercial air, land and sea vehicles.

REFERENCES:
1. Äng B, Monnier A and Harms-Ringdahl K. (2009). Neck/Shoulder Exercise for Neck Pain in Air Force Helicopter Pilots � Randomized Controlled Trial. Spine 15:544-51.

2. Äng B. (2007). Impaired Neck Motor Function and Pronounced Pain-Related Fear in Helicopter Pilots with Neck Pain � A Clinical Approach. Journal of Electromyography and Kinesiology 18:538-49. Epub 2007 Feb 27.

3. Äng B, Linder J and Harms-Ringdahl K. (2005). Neck Strength and Myoelectric Fatigue in Fighter and Helicopter Pilots with a History of Neck Pain. Aviat Space Environ Med 76:375-80.

4. Bridger RS, Groom MR, Jones H, Pethybridge RJ, Pullinger N. (2002). Task and postural factors are related to back pain in helicopter pilots. Aviat Space Environ Med. 73(8):805-11.

5. Chung SA. (2003). The molecular basis of intervertebral disk degeneration. Orthopedic Clinics of North America. 34:209-19.

6. De Oliveira CG, Nadal J. (2005). Transmissibility of helicopter vibration in the spines of pilots in flight. Aviat Space Environ Med. 76:576-580.

7. Frymoyer JW, Cats-Baril WL. (1991). An overview of the incidences and costs of low back pain. Orthopedic Clinics of North America. 22:263-271.

8. Hansen OB, Wagstaff AS. (2001). Low back pain in Norwegian helicopter aircrew. Aviat Space Environ Med. 72:161-164.

9. Hoogendorn WE, Bongers PM, De Vet, HCW, et al. (2000). Flexion and rotation of the trunk and lifting at work are risk factors for low back pain. Spine. 25:3087-92.

10. Langevin HM, Sherman KJ. (2006). Pathopysiological model for chronic low back pain integrating connective tissue and nervous system mechanisms. Medical Hypotheses. doi:10.1016/j.mehy.2006.06.033

11. Quinn KP, Winklestein BA. (2007). Cervical facet capsular ligament yield defines the threshold for injury and persistent joint-mediated neck pain. J Biomech. 40(10):2299-2306

12. Sargent P, Bachmann A. (2006). Back Pain in the Naval Rotary Wing Community. Approach.

13. Scholtz J, Woolf CJ. (2002). Can we conquer pain? Nature Neuroscience Supplement. 5:1062-67.

14. Shanahan DF, Reading TE. (1984). Helicopter pilot back pain: A preliminary study. Aviat Space Environ Med. 55:117-121.

15. Sheard SC, Pethybridge RJ, Wright JM, et al. (1996). Back pain in aircrew--An initial survey. Aviat Space Environ Med. 67:474-77.

16. Shender BS, Ostrander G, White, D. (2009). Self-reported neck pain incidence in US Navy aircrew from 2004 to 2008. Abstract in Aviat Space Environ Med. 80:291

17. Stucky CL, Gold MS, Zhang X. (2001). Mechanisms of Pain. PNAS. 98(21):11845-46.

18. Thomae MK, Porteous JE, Brock JR, et al. (1998). Back pain in Australian military helicopter pilots: A preliminary study. Aviat Space Environ Med. 69:468-73.

19. Thuresson M, Äng B, Linder J, Harms-Ringdahl K. (2005). Mechanical load and EMG activity the neck induced by different head-worn equipment and neck postures. International J of Industrial Ergonom 35:13�18

20. Thuresson M, Äng B, Linder J, Harms-Ringdahl K. (2003). Neck muscle activity in helicopter pilots: effect of position and helmet-mounted equipment. Aviat Space Environ Med 74(5):527-32.

21. van den Oord M, De Loose V, Meeuwsen T, Sluiter JK, Frings-Dresen M. (2010) Neck Pain in Military Helicopter Pilots: Prevalence and Associated Factors. Military Medicine, 175(1):55-60(6).

KEYWORDS: Low Back Pain; Spinal Injury; Air Combat Vehicles; Warfighter Protection; Modeling; Aircraft Seating Systems

** TOPIC AUTHOR (TPOC) **

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