This document provides an overview of biomechanics of the spine and hip. It discusses movements and forces acting on the spine like flexion, extension, and axial loading. Common injuries to the back like low back pain and herniated discs are also covered. Exercises to prevent back injuries and rehabilitation are described, including importance of proper lifting technique, posture, and core strengthening. Calculations are provided of torque forces on the spine during various lifting activities.

1. Department of Orthopaedic
Trauma Medicine
Year 1, Sem. 2
Subject – Biomechanics
Topic – Biomechanics of the
Spine & Hip
By
Mr. Oduor Wafulah
11th November, 2021.

2. Biomechanics of the Spine & Hip
Movements of Spine
Flexion, Rotation, Extension, Abd, Add.
Hip Movements
Elevation, Anterior & Posterior Tilt,
Flexion, Extension, Abd, Add, Hyperext,
Hyperflex

3. Spinal Deviations
Lordosis
Kyphosis
Scoliosis

4. Forces Acting on The Spine
Forces Acting On The Spine Include:
Body Weight
Tension In The Spinal Ligaments
Tension In The Surrounding Muscles
Intraabdominal Pressure
The Major Form of Loading on the Spine is:
Axial

5. Upright Position
Spinal Compression
Resulting From:
Body Weight + Weight Held
by Arms and Hands
When Standing Upright
Total Body Center of Gravity Is Anterior
to the Spinal Column.
Spine Is Placed Under Constant Forward
Bending Moment.

6. Torque
Defined: The Rotary Effect of a Force About
An Axis of Rotation, Measured as the
Producer of the Force and the Perpendicular
Distance Between the Force’s Line of Action
And The Axis
To Maintain An Upright Position
– Torque Is Counteracted by Tension in the
Back Extensor Muscles.

7. Spinal Muscles Role In Lifting
Spinal muscles have small moment arms with
respect to the vertebral joints.
Have to generate large forces to counteract the
torque produced about the spine by body weight
and objects being
Erector Spinae
Muscles

8. Why Lift With The Legs?
 Back Muscles, With a Moment Arm of Approximately 6 cm,
Must Counter The Torque Produced by the Weights of the Body
Plus Any External Loads.
Question: How Much Torque Is Developed By
The Erector Spinae Muscles With a Fm 6 cm?
 1 lb. = 4.448 Newton’s
 Segment
Head
Trunk
Arms
Box
Weight
13 lbs. (58N)
73.75 lbs.
18.2 lbs. (81N)
24.95 lbs.
Moment Arm
25 cm
(328N) 10 cm
20 cm
(111N) 40 cm
 Torque at L5-S1=
 (328N)(10cm) + (81N)(20cm) +
(58N)(25cm) + (111N)(40cm)
• = ?
 10,790 Ncm
 Force?
 0 = (Fm)(6cm) - 10,790 In static position, sum
 of the torques acting at any point is zero.
 Fm = 1798.33 N or (404.30 lbs.)

9. Problem for a 135 lb. Person
 How much force must be developed by the erector spinae with a
moment arm of 6 cm. From the L5-S1 joint center to maintain the
body in a lifting position with segment moment arms as Specified?
 Segment Weight Moment Arm
– Head 50 N 22 cm.
– Trunk 280 N 12 cm.
– Arms 65 N 25 cm.
– Box
Lifted
100 N 42 cm.
Torque ?
10,285 Ncm
Fm = 1714 N or (393 lbs. Force)
What Does The Research
• % Load Compression On
L3SDuhrinog twhe ?Upright Standing,
Lying
Down, and Sitting.
• Compression Increases More with
Spinal Flexion, and Increases
Still Further with a Slouched Sitting
Position.

10. Common Injuries Of
The Back
Low Back Pain
Soft Tissue Injuries
Acute Fractures
Stress Fractures
Disc Hernia ions
Whiplash Injuries
Low Back Pain
75%-80% of Americans
Experience Low
Back Pain Sometime During Life.
Second Only to the Common Cold
In Causing Absence In The
Workplace.
Mechanical Stress & Psychosocial.

11. Back, Spinal Column, Neck
Vertebral Column
Ribs & Sternum
SPINAL COLLUMN
7 Cervical Vertebrae
12 Thoracic
5 Lumbar
1 Sacrum - Fused
1 Coccyx - 2 Fused

12. Joints of The Vertebral Column
Vertebral Joints
–Gliding Joints - Slightly Movable
Separated By Intervertebral Disks
Thoracic Complex - Ribs
12 Sets of Ribs
Articulate With The Thoracic
Vertebrae And Sternum
7 Pairs of True Ribs - Attach Directly To Sternum
5 Pairs of False Ribs
– 2 Pairs of Floating Ribs
– 3 Pairs - Attach To Sternum via Costochondral
Cartilage

13. Sternum
Manubrium
Body
Xiphoid Process
Muscles Of The Back, Neck &
Abdomen
Deep Posteriors
Abdominals
Vertebral
Superficial Neck Muscles

14. Prevention of Injuries to Back
Posture - Standing
Hyperlordosis
Kyphosis
Posture – Sitting
– Causing Pain To Lumbo/Sacral Area
Proper Sitting Technique -
Should Not be Done Over Long
Periods of Time
Hips Should Be Flexed
Legs Should Not Be Extended
Back Should Not Be Overly Arched

15. Proper Sitting Technique -
Should Not be Done Over Long
Periods of Time
Hips Should Be Flexed
Legs Should Not Be Extended
Back Should Not Be Overly Arched
Lifting With Proper Technique
Back Kept Erect
Knees Bent
Weight Close To Body

16. Strengthening Exercises
Many Back Problems Are Caused By Weak Muscles About
The Hip And Abdominals
Weak Muscles Predispose Back To Hyperlordosis
Incorrect Sit-ups May Cause Hyperlordosis - Caused By
Shortened Iliopsoas
Stretching - Hamstrings - Iliopsoas - Quadriceps
Lumbar Spine Evaluations
Standing Evaluation
Flex Forward - Palpating Spinous Processes &
Transverse Processes
Sitting Alignment
Patellar Reflex - Lumbar 4 Involvement
Achilles Reflex - Sacral 1 Involvement

17. Lying on Back
Test Abdominals - Rectus Abdominus , Iliopsoas (Hip Flexors)
–(Static W/ Stabilized Thighs - Hip
Flex At 45 Degrees
Straight Leg Raise
– Pain When Testing Unaffected
Side - Possible Herniated Disk
– Pain When Testing Affected Side
-Possible Sciatic Nerve Stretched
Occurring With The Spine
Soft Tissue Trauma - Contusions
Nerve Inflammation Or Compressions - From Disk
Protrusions
Fractures To The Spinous Or Transverse Processes
Spondylolysis (Fracture To Interarticular Process
Spondylolisthesis (Forward Slippage Of The Vertebra

18. Other Problems Occurring With
The Spine (Continued)
Groin Strains
Hip Pointe Rs
Hip Dislocations
Rehabilitation of Back and Hip Injury
Ice Message
Movement To Regain Flexibility &
Range
Strengthening Exercises
Sit Ups & Crunches (Work Oblique's As Well)
Pelvic Tilts - (Flattening Of Back Against Floor)
Hip Lifts - (From Lying On Back Position)
Back Extensions - To 90 Degrees
Psoas & Hamstring Stretch - (Knees To Chest)

19. Questions