ELEC 371 -Orthopaedics

Bones• Structural supportJoints• MobilityLigaments• Connect bone to bone• Alignment & supportTendons• Connect muscle to bone• Energy transfer

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ELEC 371 - Orthopaedics

PeriosteumContiguous exteriorAttachment site (tendons / ligaments)Absent on articular surfaces

Cortical BoneStructural rigiditySome Blood vessels

TrabecularCancellous or Spongy BoneFew blood vessels

Marrow CavityFlexible tissueMany blood vessels

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Anatomic Axes

• actual anatomic bone path

• one for each bone

Mechanical Axes

• effective straight-line link between joint rotation axes

• one for each bone

Load Bearing Axis

• effective straight-line link between hip and ankle

• one for entire limb

• depends on limb configuration (eg. knee angle)


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Hinge

Elbow, Knee

Knuckle

Pivot

Vertebral Column

Saddle

Thumb / Finger / Toe (base of digit)

Elipsoid

Wrist / Ankle

Hand / Foot

Gliding (planar)

Hand / Foot

Vertebral Column

Ball & Socket

Hip

Shoulder


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Unlike the spine, there is no joint that provides axial rotation of any of the limbs or digits.

For example, axial rotation of the wrist involves coordinated motion of the ulna and radius.


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Photo of a THA procedure taken just after:

• the incision into the lateral hip was made

• the skin and muscle was retracted

• the femur was dislocated from the acetabulum

Damage to the head of the femur is easily visible.

This damage is too severe to heal on its own.

The joint must be replaced to restore patient mobility.


This is not the same patent as the previous photo

Pre-surgical x-ray shows

• Substantial wear of the femoral head

• Substantial damage to the acetabular cup

Post-surgical x-ray shows

• Stem implant inserted into femur

• Spherical joint fitted to implant neck


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Conventional THA surgical tools include

• hammers

• slide hammers

• broaches

• cup reamers


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Stem implants

• many lengths, widths, curvatures

• rough proximal surface for bone in-growth

• tapered neck for spherical joint interface

• proximal locking mechanisms for revision procedures

Cup implants

• rough exterior surface for bone in-growth

• screw holes

• snap-in liner


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Biocompatibility is mandatory

• rejection by autoimmune system requires immediate removal & replacement

Osteoinduction is mandatory

• if bone does not heal, mobility is never restored

Osteoconduction is desired

• implant stability is improved

• prevented by foreign substance such as bone cement

Osteointegration is desired

• eliminates need for revision surgery


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Common occurrences from hammering a stem into a thin, brittle bone shell.

Repaired by:

• wrapping with a cable and clamping the two ends

• inserting screws and/or a bracket


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ELEC 371 -Orthopaedics

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