November 2nd, 2018

// When 10 lbs. in a Backpack = 72 pounds of Force to a Student’s Spine

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Global Problem

Backpacks are standard load carriers for people of all ages, especially school children and the military. Previous studies have described the impact of the forces exerted by backpacks on load distribution, back pain, and gait. The purpose of this study was to assess the effect of forces exerted by specific backpack weights on a model of the spine. This information could be important for understanding the load that the spine experiences as an applied weight increase.

The Study

We used finite element analysis (FEA) on a model of a human spine under loads induced by carrying a backpack of different weights. We studied two different scenarios:

  1. A regular backpack with incrementally placed weights using both shoulder straps with the spine in a neutral position.
  2. A regular backpack with incrementally placed weights using both shoulder straps with the spine tilted forward by 20 degrees.

Results

Weight
Neutral Spine
20 Degrees Forward
Induced Stress
(N/m2)
(MPa)
Added reaction force
Induced Stress
(N/m2)
(MPa)
Added reaction force
(lb.)
(kg)
(N)
(lbf)
(N)
(lbf)
1
0.45
2.42E+4
(0.0242)
32.18
7.23
6.44E+5
(0.644)
51.73
11.63
25
11.34
6.05E+5
(0.605)
804.40
180.83
1.61E+7
(16.1)
1293.3
290.75
50
22.68
1.21E+6
(1.21)
1608.8
361.664
3.22E+7
(32.2)
2586.6
581.5
75
34.02
1.79E+6
(1.79)
2380.96
535.28
4.77E+7
(47.7)
3828.2
860.62
100
45.36
2.42E+6
(2.42)
3217.6
723.36
6.44E+7
(64.4)
5173.5
1163

For all of the weights examined, the axial compression force for a neutral spine was 7.2-fold the backpack weight. For the 20 degrees forward flexion condition, the axial compression force was 11.6-fold the backpack weight.

Discussion:

People everywhere have struggled to assess the impact of objects in a backpack to the body in general, and to the spine in particular.  Backpack use is associated with back pain, intervertebral disc compression, neck pain, altered posture, altered walking mechanics, and plantar foot pressure.

 

Weight of Person      Lbs. (kg.)
Conventional Recommendation
Conventional

Actual Weight Allowed Lbs.(kg.)

New Study

Force that the spine sees in neutral (lbf.)

New Study

Force that the spine sees in 20Forward Flexion (lbf.)

Estimated          6 years old
50 (13)
10% bodyweight
5 (2)
36
58
Estimated adolescent         15 years old
124 (56)
10% bodyweight
12 (6)
110
143
Estimated          young adult 18 years old
150 (68)
15% bodyweight
23 (10)
162
261
Estimated          young adult 18 years old
200 (91)
15% bodyweight
30 (14)
216
348
Estimated college aged adult
150 (68)
20% bodyweight
30 (14)
216
348
Estimated          college aged adult
200 (91)
20% bodyweight
40 (18)
288
464

 

Previous studies have suggested a safe load of 10% bodyweight in children and adolescents, 13% and 15% in young adults, and 15-20% in college-aged adults. This study focuses on the force generated to the spine.

Risk:

The first affected are the ligaments.   When the ligaments are stressed and are inflamed, then there is loss of side-by-side range of motion and stiffness. The muscles are also stressed and inflamed. Stressing a muscle makes it stronger. However persistent eccentric loading leads to intractable pain. The disc spaces are also eccentrically loaded seeing undo stresses. With persistent eccentric loading the process of wear, tear, and degeneration proceeds. Surgery may be needed.

Prevention:

One Book = 7 Books to the Spine When the force magnifiers are identified at 7X in neutral spine, and 12X in 20 degrees of forward posture, people should be careful with their contents in a backpack.

Thinking About Your Packing Pack only what is necessary. People tend to overpack and bring every possible option available in their backpacks. A person with a hoarding disorder experiences distress at the thought of getting rid of items. Now each items is shown to have consequences to the spine.

Embrace digital textbooks. Digital textbooks are easier to read, access pages, and do not transmit forces on the spine.

Embrace Neutral Alignment = Proper Posture Proper posture is the position of

“Ears above the shoulder,

Angel Wings back”, = chest open

This is the most efficient position. This proper posture includes your chin being level with the floor, your scapula retracted, and your abdomen firm. Our study shows that in neutral alignment which is good posture, the forces on the spine are 7.2X the weight. With just 20 degrees of forward posture = poor posture, the force is magnified to 11.6X the weight. This is a 60% increase in forces.

Wear Both straps. The forces on the spine are the same with one strap or two straps. Both straps allow for a division of the forces that the spine sees. Similarly, with one strap, one side sees twice the amount of forces.

Keep the Backpack Closest to The Body: Closest to the body is the most efficient position for diminishing spine forces

Develop a strong core and legs. The body provides certain inherent muscle shock absorbers. Building the core muscles with for example planking helps to strengthen the body’s force dampeners. Strong thigh muscles help.

New Technology Diminishes Spine Forces Seen in Backpacks Patented technologies (US Patent 9,700,080 B1) address the postural, ergonomic reinforcement of backpacks to diminish the forces seen by the spine with 40 – 70% efficiency.

About Dr. Ken Hansraj:

 

Kenneth K. Hansraj, M.D. is a spinal and orthopedic surgeon specializing in cervical, thoracic and lumbar procedures, bloodless spine surgery, minimally invasive spine surgery, laminectomies and spinal fusions. He believes in whole body wellness, preventative care and that the spine is a principal indicator of general health impacted by “human software and hardware.” Dr. Ken is the author of the internationally bestselling book, Keys to an Amazing Life: Secrets of the Cervical Spine, which he was inspired to write based on this concept. Dr. Hansraj is also the author of Bloodless Spine Surgery: Pictures and Explanations. His goal with each of his books is to bring years of accumulated expert medical knowledge to the public at-large in an easy-to digest format and to help countless individuals with ongoing spinal and health issues. Dr. Ken Hansraj is TV and media trained and has extensive experience with national outlets such as CNN, HLN, CBS, FOX, NBC, ABC, NPR and has been featured globally. Cision® estimates his current media impressions at 7 Billion.

Chief of Spine Surgery

New York Spine Surgery & Rehabilitation Medicine

Attending Orthopedic Surgeon

Vassar Brothers Medical Center, Hudson Valley, NY

Fellowship Trained in Minimally Invasive Spinal Surgery

California Center for Minimally Invasive Spinal Surgery; Thousand Oaks, CA

Fellowship Trained in Spinal and Scoliosis Surgery

The Hospital for Special Surgery, New York, New York

Fellowship Trained in Orthopædic Biomechanics

The Hospital for Special Surgery, New York, New York

Board Certified, ABOS

American Board of Orthopedic Surgeons

Board Certified, ABMISSM

American Board of Minimally Invasive Spinal Surgery & Medicine

Board Certified, NMBE

National Board of Medical Examiners

 

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