Ligaments. A Source of Work Related Disorders STAR Symposium Do not copy or reproduce in any form

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1 Ligaments A Source of Work Related Disorders

2 M. Solomonow, PhD, MD (hon) Occupational Medicine Research Center Bioengineering Laboratory Department of Orthopaedic Surgery Louisiana State University Health Science Center New Orleans

3 Ligaments Are the Major Restraints of the Joints e.g. Keeping Bones Connected to Each Other Keeping Bones Moving Relative to Each Other on a prescribed Track Keeping Even Articular Surface Contact and Pressure

4 Ligaments are composed of collagen fibers with helical wave along their axis Some fibers have deeper waves than others

5 Stretching a Ligament Results in a Fiber Recruitment Process Fibers with shallow wave straighten out first and become stiffer Fibers with gradually deeper wave stretch progressively to result in gradual stiffening

6 X1 X2 TENSION X3 Recruitment Fully Active X1 X2 LENGTH X3

7 Net Effect is a Non-linear Length-Tension Curve

8 Collagen is a viscoelastic substance As such it displays a common behavior consisting of: - Creep - Tension Relaxation - Hysteresis - Time/Frequency Dependent Length Tension All of which lead us to suspect that disorders will be present with time, stretch and load

9 Tension Relaxation and its Recovery Example: 20 Minutes of static or cyclic stretch results in tension relaxation which does not fully recover after 7 hours rest

10 1.2 Normalized Tension Tension-Relaxation Elongation Rest 14 Displacement (mm) Time (min)

11 Creep and its Recovery Example: 20 minutes of static or cyclic load application result in creep which does not fully recover after 7 hours of rest

12 Normalized Displacement Creep Residual Creep Loading Rest Load (N) Time (min)

13 Ligaments Are Sensitive to Strain Rate Slow rate elicits low tension Fast rates elicits high tension

14 % / s 100% / s 40 Tension (N) 30 50% / s % / s Displacement (mm)

15 Hysteresis Ligaments display hysteresis of the length-tension behavior during cyclic loading e.g. length-tension is not on the same curve during stretch and release

16 50 A 50 B TENSION (N) LOAD (N) DISPLACEMENT (mm) ELONGATION (mm)

17 Ligaments display cumulative build up of creep in work-rest periods - Due to long recovery time needed to restore resting length

18 Normalized Displacement CUMULATIVE CREEP RESIDUAL CREEP WORK-REST DURATION REST Load (N) Time (min)

19 Ligaments behavior is sensitive to frequency of loading or stretching in repetitive task - Higher frequencies result in larger creep

20 20 15 Displacement (mm) Hz 0.5 Hz Time (min)

21 In General Moderate Physical Activity Followed with Sufficient Rest Result in: Collagen Fiber Hypertrophy (Number, Diameter, Metabolism ) Increase in Maximal Strength

22 IMMOBILIZATION Loss of Collagen Fiber Robustness Number, Thickness, Tension etc Result in Weak, Atrophied Ligaments

23 IMPORTANCE Return to Work After; Long Sickness Unemployment Long Holiday Require Slow Build Up of Exposure to Physical Activity

24 Ligaments Are Sensors

25 Afferents Found in Ligaments Are Common to Kinesthetic and Proprioceptive Sensation Golgi Pacinian Ruffini Bare Nerve Endings

26 Ruptured or Injured Ligaments cause: Impaired motor functions Loss or impaired sensation Pain Lead to: Deficient function Risk of additional injury

27 Afferents in Ligaments Trigger a Reflex Activation of Associated o Guanche 1995 Muscles o Petrie 1997, 1998 o Solomonow 1987, 1998, 2001,2002 o Stubbs, 1998 o Knatt, 1995 o Dyhre-Poulsen, 2000

28 o Creep o Tension-relaxation o Hysteresis o Time/frequency dependency All Lead to: Shift in sensation thresholds Impaired sensation Impaired reflex muscular activation

29 For Example: Cyclic Loading of the Lumbar Spine Develops Creep in the Ligament, over time, result in: Decreased reflexive muscle activity Spasms Initial hyperexcitability in following rest Delayed hyperexcitability Recovering muscular activity during rest

30 1.0 EMG (mv) Displacement (mm) Load (N) /6 1/ Time (min) Time (hr)

31 3 N = 6 NIEMG N Displacement (mm) Time (min)

32 Five Component Neuromuscular Disorder

33 NIEMG NIEMG Spasms Initial Hyperexcitability Morning After Effect Spasms Initial Hyperexcitability Morning After Effect Time (Min)

34 Sources of the Neuromuscular Disorder: Creep Microdamage in Collagen Fibers Results in: Spasms During Creep Development Initial Hyperexcitability During Rest

35 Creep Microdamage Inflammation Results in: Delayed Hyperexcitability

36 Cat Control Vessel Neutrophils Vessel Ligament

37 Neutrophils / mm 2 Control 20 minutes 2 hours 7 hours 3,680

38 Creep Acute Inflammation (Comulative Creep) dt Chronic Inflammation

39 Dose - Duration to Elicit Chronic Inflammation is not known

40 Chronic Inflammation is a Permanent Disability Pain Muscle Stiffness Weakness of Affected Joint

41 Conclusions Creep, Tension-relaxation, Hysteresis and Time/Frequency Dependence of Ligaments is a Source of Mechanical Joint Laxity Problems Articular Surface Injury Potential Self Injury Potential Injury to capsule, tendons, nerves and nearby tissue

42 Conclusion (Cont.) As Organs in the Sensory-Motor Loop, the Same Mechanical Problems are a Source of Deficient sensation Complex Disorders Impaired motor performance Deficient synergy/reflex muscle activation Spams and Hyperexcitability Inflammation & neurological Implication Permanent disability

43 *Supported by: National Institute of Occupational Safety and Health Grants R01-OH & R01-OH Louisiana Board of Regents Center Grant HEF ( )-07