3.2 Conceptual Overview of Orthopaedic Biomechanics

(Reading assignment: [@Bartel2006] Chapter 1.

3.2.1 The human body as a machine

  • The human body is a machine!
    • A combination of rigid and resistant bodies
      • Bones and the soft tissue associated with them
      • Links are joints which have low friction and transfer large forces
    • Large, precise and imprecise motion
    • Performs useful work

Contrasting humans with most machines

  • Most joints have imprecisely defined motion
    • There is flexibility in the soft tissues (ligaments, muscles)
  • This flexibility leads to coupling between loads and motion:
    • i.e. the motion can effect the loads in ways that do not typically occur in “conventional” machines
    • Changes in force will produce changes in joint motion,
    • Changes in relative position between bones (at joint) will change the forces in the joints
    • “sloppy joint”

Joints, range of motion and, precision

  • Hip joint
    • is more rigidly defined by its bony ball and socket
    • widely varying soft tissue restraint… but less reliance

  • Shoulder joint
    • is very imprecisely defined with its ball and socket
    • widely varying soft tissue restraint…
    • requires more soft-tissue control and precision placement

Unlabelled Image Missing

Unlabelled Image Missing1

“Osteoporosis is the leading cause of age-related kyphosis, with sarcopenia, or age-related muscle loss, being a secondary cause,” Patel explains.2

  • Skeletal loads vary from person to person and over time in a particular person
  • Aging and disease change skeletal response
  • We are not often concerned about precise loads, stresses, etc,
    • rather we compute approximate loads within a level of uncertainty
  • We seek to describe the fundamental behavior of the system
    • Use engineering methods to understand the effect of damage and disease
    • Predict, understand, and influence the methods and techniques used to restore function
  • The skeleton has an amazing ability to repair damage and adapt to physical demands

Unlabelled Image Missing 3

Non-surgical treatment with a brace. Many humerus fractures can be treated without surgery. The humerus shaft fracture above was successfully treated in a “Sarmiento brace”, which wraps around the upper arm and holds the bone aligned while it heals.4

  1. https://health.usnews.com/wellness/articles/2018-08-17/older-adults-heres-what-causes-hunchback-and-how-to-prevent-it↩︎

  2. https://health.usnews.com/wellness/articles/2018-08-17/older-adults-heres-what-causes-hunchback-and-how-to-prevent-it↩︎

  3. https://www.schreibermd.com/humerus-fracture↩︎

  4. https://www.schreibermd.com/humerus-fracture↩︎