The Use of Musculoskeletal Modelling to Assess Head- Worn Mass Properties

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1 The Use of Musculoskeletal Modelling to Assess Head- Worn Mass Properties SAFE Europe 2017 Dr Ross D Pollock 4/5 th April

2 Neck Pain Prevalence and Contributory Factors Neck pain is a common complaint amongst aircrew: 70 % in fast jet (FJ) aircrew 57 % in front rotary wing (RW) aircrew 71 % in air load masters Most commonly reported causative factors are: Use of helmets/head mounted equipment (NVG) Postures adopted during flight Gz exposure Neck pain/injury and muscle Loading of muscles may cause tenderness, strain, spasms, micro-damage or rupture Muscle fatigue Inappropriate loading of muscles or other structures 2

3 Why Use Modelling An understanding of how muscle responds to external loading may be beneficial in identifying means to reduce fatigue and mitigate neck pain/injury risk Difficult to achieve experimentally Aim Do determine whether musculoskeletal modelling can be used to assess differences in muscle force output in response to changes in head mass properties 3

4 Software for Interactive Musculoskeletal Modelling (SIMM) Full body model representative on an average male 100 degrees of freedom 156 joins 284 muscle-tendon actuators Contains detailed head and neck model Muscle architecture obtained from MRI imaging Cadaveric studies to identify muscle morphometry Default settings can be altered Helmet segment added 4

5 SIMM Modelling: Motion Files Static modelling conducted Anatomical range of motion modelled in 10 increments in pitch, roll and yaw ± 50 Pitch:- head flexion / extension ± 40 Roll:- head lateral flexion ± 60 Yaw:- head rotation 5

6 SIMM Modelling: Model Head Parameters Naked head (4.005kg) to Head + 5 kg Backward Forward (±5 cm) Up Down (±5 cm) 6

7 SIMM Modelling: Muscles 26 muscles on left side of neck modelled Muscle force output Maximal muscle force Simulations for each head mass property and posture takes ~10 min ~1,116 simulations performed No. Muscle Group Muscle M1 M2 M3 M4 M5 M6 Sternocleidomastoid Scalene Sterno-mastoid Cleido-mastoid Cleido-occipital Scalenus anterior Scalenus medial Scalenus posterior M7 Longus Capitis Longus capitis (skull-c4) M8 M9 M10 M11 M12 M13 M14 M15 M16 M17 M18 Longus Colli Trapezius Splenius Erector Spinae Longus colli (C1-thorax) Longus collli (C1-C5) Longus colli (C5-thorax) Trapezius clavicular head Trapezius acromial head Splenius capitis (skull-c6) Splenius capitis (skull-thorax) Splenius cervicis (C3-thorax) Semispinalis capitis (skull-c5) Semispinalis capitis (skull-thorax) Semispinalis cervicis (C3-thorax) M19 Levator Scapulae Levator scapulae M20 M21 M22 M23 M24 M25 M26 Erector Spinae Rectus Capitis Posterior Obliquus Capitis Longissimus capitis (skull-c6) Longissimus cervicis (C4-thorax) Iliocostalis cervicis (C5-rib) Rectus capitis posterior major Rectus capitis posterior minor Obliquus capitis superior Obliquus capitis inferior 7

8 Output: Response to Mass 8

9 Output: Response to CoM displacement 9

10 Muscle Sensitivity and Force Production (2) 10

11 Findings It is assumed that by reducing muscle force production fatigue onset can be delayed and this may help mitigate against neck pain and injury To reduce muscle force production: Minimise mass of helmet (<2 kg to prevent high forces) Position CoM rearward and/or below neutral head CoM If > 30 of flexion is held for long periods (e.g. RW aircrew) prioritise minimising helmet mass over moving the CoM Implications for counterbalances Difficult to extrapolate results to RW rear aircrew that are not in a neutral seated/standing posture 11

12 Helmet Modelling Assessed suitability of SIMM to evaluate different helmets Examined muscle force production in response to 10 different helmets/configurations Helmet/configuration associated with lowest muscle force assumed to have lower risk Position of CoM from C1/Head (m) Configuration Mass (kg) Longitudinal Vertical Lateral Bare head H H H H H H H H H H

13 Modelling Default model parameters used Helmet segment defined based on mass and CoM measurements Assessed roll, pitch and yaw in 10 increments ± 50 Pitch:- head flexion / extension ± 40 Roll:- head lateral flexion ± 60 Yaw:- head rotation 10 muscles located on left side of neck selected Based on previous SIMM modelling Reduces processing time Muscle force output obtained Muscle Group Trapezius Splenius Erector Spinae Erector Spinae Muscle Trapezius clavicular head Trapezius acromial head Splenius capitis (skull-c6) Splenius capitis (skull-thorax) Splenius cervicis (C3-thorax) Semispinalis capitis (skull-c5) Semispinalis capitis (skull-thorax) Semispinalis cervicis (C3-thorax) Longissimus capitis (skull-c6) Longissimus cervicis (C4-thorax) 13

14 Extension Analysis Semispinalis Capitis Pitch Flexion Angle ( ) Bare Head H1 H2 H3 H4 H5 H6 H7 H8 H9 H % 83% 84% 83% 83% 84% 84% 84% 84% 84% 84% % 81% 82% 78% 77% 86% 84% 88% 87% 87% 88% % 92% 93% 89% 87% 93% 93% 93% 93% 93% 93% % 97% 97% 93% 89% 98% 98% 98% 98% 98% 98% % 88% 86% 81% 77% 96% 91% 102% 97% 102% 102% 0 40% 72% 68% 64% 61% 79% 73% 84% 79% 88% 88% 10 28% 53% 48% 45% 42% 59% 52% 64% 58% 70% 69% 20 15% 34% 27% 24% 22% 39% 31% 43% 35% 50% 46% 30 0% 5% 0% 0% 0% 6% 1% 8% 3% 13% 10% 40 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 50 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 14

15 Extension Flexion Analysis (2) Angle ( ) H1 Score % % % % % % % % % % % 1 Sum 25 Pitch Score 2.27 Pitch Roll Yaw Trapezius clavicular head Trapezius acromial head Splenius capitis (skull-c6) Splenius capitis (skull-thorax) Splenius cervicis (C3-thorax) Semispinalis capitis (skull-c5) Semispinalis capitis (skull-thorax) Semispinalis cervicis (C3-thorax) Longissimus capitis (skull-c6) Longissimus cervicis (C4-thorax) Axis Score Total Score A lower score indicates lower levels of muscle activation for a given configuration across the full range of motion in all axes of movement 15

16 Helmet Ranking Helmet Mass Score Ranking (combined) Muscle forces H Lowest H H H H H H H H H Highest H4 is the best helmet for minimising muscle force H2 H4 are different configurations of same helmet H9 and H10 were consistently ranked poorest 16

17 Relevance Increased Force Generation by Muscle Compensation by other muscles or tissues Pain/Injury Fatigue Inability to Compensate for Applied Loads In general it is assumed that a helmet configuration associated with higher levels of muscle force would be more likely to result in neck discomfort/pain Overall H2 H4 (different configurations of same helmet) would be anticipated to reduce risk of pain and discomfort Unknown effect size Only static conditions across a large range of motion modelled Still comparable between helmets 17

18 Acknowledgments Conducted / Supported the Work: Dr Mike Llewellyn Mr Ken Puxley Mr David Bigmore Project Sponsors: 18

19 Any Questions? 19