Week 3 Sitting & Lifting Biomechanics

SPINE surrounded by 3. NERVES

- Branch off from the spinal cord - Transmit info to and from the brain - EXPLAIN WHY SCIATICA PAIN IS FELT IN THE LEGS - Travel from the spinal cord to the legs and feet

SPINE made up of 2. DISC

- Kidney shaped - Separate vertebrae - Act as shock absorbers?? - Made of cartilage - Allow movement of the spine - Has an annular outer fibrous elasticity layer and several more layers internally - Nucleus Pulposis with fluid in the center, similar consistency to toothpaste - Always under pressure - Have very little blood or nerve (Recurrent Meningeal Nerve) supply *Nucleus Pulposis will not protrude unless annular fiber tear

SPINE made up of 3. FACET JOINTS at rear of vertebrae

- Small sliding joints - Cannot take a lot of weight - Help to restrict and control movement of the spine - Protect discs from excessive bending and twisting - Form part of the vertebrae that enclose the spinal cord

SPINE surrounded by 1. LIGAMENTS

- Tough fibrous tissue connecting one bone to another - Restrict excessive movement of joints - Can be damaged if overstretched - CREEP: put in a position long time, loose ligaments allow disc relationship with structure

HERNIATED DISC

1 - 5% of back pain is a HERNIATED DISC Posterior protrusion of the nucleus pulposus tend to cause CENTRAL CORD problems Posterior-LATERAL protrusion of the nucleus pulposus tend to cause NERVE ROOTS problems Usually at C5/C6, C6/C7, L4/L5, or L5/S1

LIFTING TIPS

1. Decrease weight of objects (e.g. order supplies in smaller quantity containers) 2. Use team lifting for large or heavy objects 3. Change activity (e.g. pull or push rather than carry) 4. Minimize horizontal distances between start and end of lift (e.g. several shorter carrying distances rather than one long one)

LIFTING TIPS

5. Stacking material no higher than shoulder 6. Heavy objects at knuckle height 7. Reduce frequency of lifting 8. Use rest periods 9. Job rotation to less strenuous jobs 10. Handles on containers

Biopsychosocial Model of Disease What is it?

A framework that states that interactions between BIOLOGICAL, PSYCHOLOGICAL, SOCIAL factors determine the cause, manifestation, and outcome of wellness and disease

3 Main Functions of Spine 3. Allow MOVEMENT

Allows it to be FLEXIBLE therefore allowing TWISTING and BENDING. Muscles control these movements

Office Desk & Disc Force

BEST to WORSE Relaxed Back Writing / Depression of Pedal Arms Hanging Type Writing Lifting Weight

Chair & Disc Force

BEST to WORSE Standing at ease (least force goes to disc) Sit Straight / Relaxed Arms Supported Relaxed Feet Unsupported Sitting Relaxed Sitting Posterior Sitting Anterior Straight Sitting Anterior (lean forward)

SPINE made up of 1. VERTEBRAE

Bone structure (connected to each other by ligament) which form 3 curves - Neck, back and small of back

CAUSES OF INJURY 2. HEAVY / EXCESSIVE LOAD

Can cause excessive strain on the lower back region and on discs Static muscle work is used

CAUSES OF INJURY 3. BENDING / STOOPING

Causes injury because the discs are under pressure out of their natural position. Static muscle work.

What is the FUNCTION of the MOTION SEGMENT?

DISC is composed of 1. Annulus Fibrosus - supplied by meningeal nerve - functions as a coiled spring, holding the vertebrae together 2. Nucleus Pulposus - functions as a ball bearing the vertebrae roll over during flexion, extension, and lateral bending *Increased annulus fibrosis stiffness can increase lumbar lordosis

CAUSES OF INJURY 1. STATIC MUSCLE WORK

Does not necessarily mean standing or working still When a muscle is working but not moving for example holding a pint glass. Muscles are more prone to injury when static due to the lack of blood passing through them hence reducing oxygen and nutrients which causes a build up of waste products such as lactic acid. This leads to fatigue and the muscles become more prone to injury at this point

CAUSES OF INJURY 4. BALLISTIC MOVEMENTS

Doing something sudden and fast Muscles over-contract Muscle with previous injury tear again

INJURY CAUSATION PROCESS 1. STRESS

Excessive Loads Awkward Postures Repetitive Tasks Static Postures

What STRESS does flexion, extension and lateral bending cause the MOTION SEGMENT?

Flexion / Extension & Lateral (sideways) Bending create COMPRESSIVE STRESSES on one side of the DISC & TENSILE on the other.

What stress does forces or force components PARALLEL to discs cause?

Forces or force components parallel to discs also create SHEAR STRESSES on the the discs causing them to "SLIP" in the direction of the force

Arm Rest & Forward Movement on Disc Force BEST PRACTICES

GREATER Backrest Inclination Angle results in LOWER Muscle Activity Lessens need for spinal support from Erector Spinae Muscle Lower EMG signal activity Prevent Fatigue Arm rest No Forward Movement

INJURY CAUSATION PROCESS 3. SOFT TISSUE SHORTENED

Go into spasms, contract

INJURIES 2. DISC HERNIATION

Herniating disc compressing spinal canal space

BIOMECHANICS LEVERS How lever is created?

Holding loads AWAY from the body creates a LEVER effect on the spine which in turn INCREASES the load capacity which is placed on the spine - particularly in the lumbar region.

Biopsychosocial Model of Disease What is the Benefit?

Holistic evaluation

Backrest & Lumbar Support

Inclination Angle - Forward (BAD) - Straight Up (Better) though facets might corp a bit - Backrest is back: take the weight of upper body off the lower body Lumbar Support - GOOD when sitting upright

3 Main Functions of Spine 2. SUPPORTS Upper Body

Includes the head, arms, ribs etc the weight is has to support can be considerable certainly on the lumbar spine

Changing Posture

Increased low back pain (LBP) risk for people required to sit or stand for prolonged periods of time Best to Change Work Posture and/or occupational task FREQUENTLY to prevent "Postural Fixity" 10-15 minute BREAKS for every 2 hours seated work

TYPES of SPINAL INJURIES 1. CUMULATIVE

Injuries that have been sustained over a period of time by things such as - Poor Posture, - Repetitive Movements, - Twisting and Asymmetry, - Static Muscle Work etc. Degeneration of discs due to age can also be a contributing factor to cumulative injuries

LIFTING TIPS Lifting Distance

Keep weight close to body

Describe the TYPICAL LOAD CHARACTERISTICS for L5 & S1 FACET JOINTS

L5 and S1 sits deep like a valley in between iliac crest, ilio-lumbar ligament provides stability Sustain LARGEST contact forces from upper body weight L4 and L5 are more prone to injury, sits near coccyx, less stable due to less protection from ilio-lumbar lig. Results in long-term degeneration

Arm Rest & Forward Movement on Disc Force DO NOT PRACTICE

LOWER Backrest Inclination Angle results in HIGHER Muscle Activity More need for spinal support from Erector Spinae Muscle Higher EMG signal activity Fatigue Arms hanging Forward Movement

Workplace back Injuries occurs mainly in what part of the spine? Why do you think this is the case?

LUMBAR spine because this area carried more load.

INJURY CAUSATION PROCESS 2. SOFT TISSUE OVERLOAD

Ligaments Muscles Tendons

What is the STRUCTURE of the MOTION SEGMENT?

Motion Segment is the functional unit of the spine Composed of 2 vertebrae and its associated soft tissues. It is important to understand the 3 joint complex (1 disc and 2 facets).

SPINE surrounded by 2. MUSCLES & TENDONS

Muscles - control the body's movements they are attached to bones by tendons - work in pairs, as one contracts then another relaxes to allow movement. - use energy when relaxing or contracting

LIFTING & CARRYING STYLES ONE HANDED LIFT & CARRY

NEGATIVE Musculoskeletal Load

LIFTING & CARRYING STYLES TORSO / TRUNK LIFT & CARRY

NEGATIVE Musculoskeletal Load - Heavy backpack pushes trunk forward

LIFTING & CARRYING STYLES STOOP BACK LIFT

NEGATIVE Musculoskeletal Load - Stooping - Weight too far away from body

LIFTING TIPS Lifting & Twisting

NEVER DO IT Disc force is tripled

TYPES of SPINAL INJURIES 2. SUDDEN / IMMEDIATE / TRAUMATIC

One off accidents, Over exertion

CAUSES OF INJURY 5. ASYMMETRICAL POSTURE

One side of the body not balance with the other side IT IS BETTER TO BALANCE WITH A SIMILAR WEIGHT IN THE OTHER HAND

LIFTING & CARRYING STYLES SQUAT LEG LIFT

POSITIVE Musculoskeletal Load - Bend knees - Keep weight close to body - Preferably light weight - Use legs when lifting to decrease lumbar lordosis - Protect disc - No flexion

LIFTING & CARRYING STYLES Lift Weight from Table

POSITIVE Musculoskeletal Load - Weight close to body - Adjust with patient close to table to place less stress on spine - Use legs to lift weight NEGATIVE Musculoskeletal Load - Stooping to lift weight from a LOWER table

BIOMECHANICS LEVERS How to prevent injury?

Prevent LEVERAGE and DECREASE LOADING on the spine by: · Organising the work to REDUCE the EFFECT of LEVERAGE. · Keep loads CLOSE to the BODY · Try not to STOOP SYMMETRY, BALANCE, ADAPTABILITY

Describe the TYPICAL LOAD CHARACTERISTICS for DISC

Provide about 40% of spine's ability to RESIST ROTATIONAL TORSION and SHEAR Compressive force of normal lordosis protects lumbar disc

Describe the TYPICAL LOAD CHARACTERISTICS for FACET JOINTS

Provide about 40% of spine's ability to RESIST ROTATIONAL TORSION and SHEAR Sustain about 30% of VERTICAL COMPRESSIVE LOADS on the spine **Facet joints must NOT bear weight or they will break down 15-30% of low back pain emanates from facet joints

CAUSES OF INJURY 6. Others

Repetitive of tasks Degeneration of discs Individual concerns Duration of tasks

INJURY CAUSATION PROCESS 4. INJURY

Repetitive strain

What STRESS does RIGHT LATERAL BENDING cause the MOTION SEGMENT?

STRONG INTACT ANNULUS - DISC bulge on RIGHT - nucleus pulposis shift to right - tensile stress on the left keeps annulus bulging to left TEARING IN ANNULUS - tensile stress does not exist - DISC will bulge to LEFT

What stress does spinal ROTATION cause the MOTION SEGMENT?

Spinal Rotation creates SHEAR STRESSES that "TWIST" the DISC FIBRES around its periphery, with LARGEST "SHEAR" on the OUTSIDE.

3 Main Functions of Spine 1. PROTECTS the Spinal Cord

Spinal cord runs vertically through the centre of the spine and is protected by the vertebrae

INJURIES 1. DISC PROTRUSION

Takes long time Micro-trauma Nerve root being compressed against bone Fibrous ring tear Pain is referred Gelatinous structure protruded

BIOMECHANICS LEVERS What is the effect of lever on body?

The EFFORT required by the BACK MUSCLES INCREASES according to how FAR the load is held AWAY from the body.

Describe the TYPICAL LOAD CHARACTERISTICS for FACET JOINTS & DISC

The facets and discs SHARE the load. Neither should take 100% of the load. This may happen with an increase or decrease lumbar lordosis (for example).

Biopsychosocial Model of Disease What are the Limitations?

Very broad Does not guide, recommend or restrict which features should be evaluated Attitudinal bias of Clinician: is free to choose from a variety of tests Does not inform on how one domain may or may not influence or interact with another domain

Describe the ADVANTAGES of a CORRECT SITTING POSTURE

Weight Transfer - Main body weight transferred to seat. - Some transferred to floor, backrest, and armrests. - Feet are on the floor Advantages - provides STABILITY to tasks involving visual and motor control - less ENERGY consuming than standing - places less STRESS on LOWER extremity joints (ankles & knees) - lessens PRESSURE on lower extremity circulation

Describe the BIOMECHANICS of the lumbo-pelvic area as the TRUNK FLEXES?

When bending forward 1. REVERSAL of the LUMBAR LORDOSIS 2. TRANSVERSE movement of the PELVIS around the HIPS 3. HIP JOINTS allow further flexion at the end. (slide 12)

TRUNK MOTION

When trunk flexes, the 1st 50 - 60 degrees of motion occurs in LUMBAR SPINE Spinal Flexion Pelvic Tilting Movement in lumbar spine, in SI joint, hips Pelvic Stabilisers (gluts, hamstrings, quadriceps)