Talk Title: Shoulder strength ratios determine injury risk and a focused engineered solution

Speaker Name: Cindy Lawton

Speaker Title: BCPE, PT, OCS, MA (LA-UR-15-22284)

Outline• Injury information – Glovebox worker data

• Shoulder anatomy and muscle length bio-mechanics

• Rotator cuff ratios and results

• Engineering solution

Person WorkEnvironment

Stress/Job satisfaction

Money

HabitsOutside Activities

Body Type

Exercise

Pre-existing Conditions

Job Tasks

Equipment

ShiftBreaks

Communicating Needs

Management Support

Nutrition

Who is going to get hurt?

LANL Glovebox

• 700 Operating Gloveboxes • 400 trained glovebox workers• 150-200 daily workers

5

Pencil Drop – Typical GB Activity

Percentage of Workers Reporting Symptoms vs.

Years as a Glovebxox Worker.

0

10

20

30

40

50

60

70

80

90

100

Years As a Glovebox Worker

Perc

enta

ge o

f Wor

kers

Rep

orti

ng S

ympt

oms

<3 3-5 >5-10 >10-15 >15-20 >20-25 >25

Repetitive Injuries

Glovebox Injury Data

*2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

0

2

4

6

8

10

12

14

16

18

20

first aid RecordableLeading indicator

Lagging Indicator

ZERO

Injury Information

• Previous 18 months before 2006 – 18 recordable injuries

• Since 2004 – 57 recordable glovebox injuries

Shoulder and Elbow

1. Highest severity – surgery and career ending

2. Highest frequency ( 23 shoulders & 35 elbows)

3. Most costly : Shoulder surgery direct and indirect cost $120,000 to

$200,000 approximately

Elbow surgery direct/indirect cost$100,000 approximately

Muscle Length Tension

11

Mid-range – muscle is capable of producing optimal force

Shortened Muscle(Too much overlap)

Mid-range Muscle(Optimal overlap)

Lengthened Muscle(Too little overlap)

Cross-Linking of Myofibrils

12

GB worker - Muscles of the Mid-Back

This is copyrighted© 1999 by Wesley Norman, PhD, DSc

GB Worker - The Rotator Cuff

Most glovebox-related shoulder injuries involve the rotator cuff

Slide 13

Strength Ratios

Healthy shoulders - 1.5 : 1 or 3 : 2 ratio of internal rotator strength to external rotator strength

Testing Strength Ratios

• The arm position: 30º of forward flexion and 30º of abduction

• Worker pushed into forcegauge/researcher stabilized arm

• Utilized the average of 3 trials for both Int Rot. and Ext Rot. to determine ratio.

Shoulder Ratio ResultsGlovebox workers have shoulder strength ratios significantly different from the healthy norm of 1.5 (α = 0.0001)

Range: 1.5 to 4.1 Mean: 2.7

Shoulder Ratio Results

Shoulder Ratio Results • Right shoulder ratios were more aberrant than

left

Right mean: 2.8 Left mean: 2.6

Slide 18

Shoulder Ratio Results – Symptoms

• The majority of workers with ratios ≤ 2.5 were asymptomatic

• Symptom incidence increased in workers with ratios ≥ 2.5

Slide 19

Ratios – symptoms – years GB work

Study Summary

• Glovebox workers have shoulder strength ratios significantly different from the healthy norm

• Only 2% of GB workers have the healthy 1.5 ratio

• Symptomatic workers have ratios that are more skewed than those of asymptomatic workers – especially early in career

Solution Development

Glovebox tasks that stress the shoulders:• Lateral transfer of items - passing items down the

length of a glovebox

• Heavy lifting - items heavier than 15lbs

• Repetitive motions - cleaning windows

Activity at extreme range of motion - transferring items into/out of airlocks

Air lock – Transfer Tunnel

Location of an airlock

Shoulder Position.

Air Lock Sliding Tray

$ 175,000 to design and manufacture the trays.

Summary• There is prevalent imbalance in shoulder strength ratios among GB

workers.

• Symptoms are more prevalent among workers with more aberrant shoulder strength ratios.

• The abnormal ratios are most likely contributing to shoulder symptoms especially early in a GB workers career.

• Utilizing strength ratios can be utilized both as a medical screen as well as to initiate engineering control projects.