HEADPIECE PLACEMENT.

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HEADPIECE PLACEMENT.

• Lee G. Yardley, D.C.

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• In correcting or reducing the misalignment
  factors of the ASC you have only 2 tools at your
  disposal-
• The vector.
• Head piece placement.
• The determination of how to best use these tools
  is developed as a result of a thorough
  understanding of the biomechanics of the case .
• Today we are going to address the practical
  aspects of the headpiece placement component .

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• The headpiece controls 2 things-
• The direction of head movement.
• The speed of head movement.
• The direction of head movement can occur in one
  of 3 ways
• Movement away from the side of contact/laterality
• Movement towards the side of contact/laterality.
• No movement at all.

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OUR TOOL THE MASTOID SUPPORT HEADPIECE

• Lets take a look at the makeup of the headpiece.
  It has two different ends.
  
• The round end
• A B
  C
• The square end
• These are labeled A,B,C D headpiece positions.
  

D
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WHERE IS THE CENTER OF GRAVITY OF THE SKULL ( COG)

• CENTER
  OF GRAVITY
• -----------------------------------------------
  ----------------------------------------------

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• The center of gravity of the skull is about ½
  inch or 1 cm above the external auditory meatus
  in the saggital plane.
• This translate to the center of the orbits of the
  eyes in the frontal plane.
• If you want no head movement at all then you
  would place the COG of the skull on either the
  center of D or squarely on B.
• If you want the head to move away from the side
  of laterality then you would want the COG to be
  above D on the round headpiece, or above B
  towards C on the square headpiece.
• If you want the head to move towards the side of
  laterality then you would want the COG of the
  skull to be below D on the round headpiece, or B
  towards A on the square headpiece.

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• The speed of head movement can be modified two
  different ways-

1. By modifying the length of the lever arm created
   between the COG of the head the fulcrum
   established by the mastoids contact with the
   headpiece.

2 Increasing the resistance to the head moving
by increasing the surface area contact between
the head the support.
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• So the further that we move the center of gravity
  above the fulcrum the faster the head will move
  away from us during the adjustment.
• The further we move the head below the fulcrum
  the faster the head will move towards us during
  the adjustment.
• This is true in a very pure sense on the D
  headpiece but on the square headpiece we have the
  additional factor of the resistance created by
  the surface area contacting the greater area
  offered by the square headpiece.

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• The resistance offered by the square headpiece
  increases the number of possible options offered
  dramatically.
• While the head will still move in the direction
  based on how far above the fulcrum the COG is, it
  will encounter some level of resistance that
  slows down the head movement. This can provide
  time during the adjustment for other things to
  occur.
• Whilst it is true that if you altered the lever
  arm shortening it by moving the COG of the head
  towards the fulcrum you might have the same net
  effect, the resistance offered by the square
  headpiece provides more room for error.

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FINER POINTS OF ACCURATE HEADPIECE PLACEMENT.

1. The episternal notch the glabella must be level
   with each other.
2. The chin should not drop down. The superior
   occlusal plate should be parallel with the bottom
   of the headpiece.
3. As you are adjusting the case, if you sense (
   based on feedback) that it is not moving then
   gently lift the patients head place it back.
   This can ever so slightly change the interface of
   the articulations then pull through a few more
   times. You may well find that it begins to move
   again.
4. If it is still not moving the you might try
   moving the crank a quarter or half of a turn
   then pull through a few more times. Simple things
   like these can make all the difference to
   reducing the subluxation.

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• If you make the distance of the COG from the
  fulcrum too large then you may well lock up the
  articulations move nothing.
• Another factor that may well lock up the
  articulations is too much angulation of the
  headpiece.
• Angulation of the headpiece is defined as A
  angulation or B angulation-
• A angulation
  B angulation

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Achieving the Correct Angulation

• You do need to be careful not to have too great
  of angulation.
• The rule of thumb for both A B is the you must
  be able to slide your hand touch the pinna of
  the ear without lifting the patients head. This
  will protect you against Parietal support which
  will negate all of your lever systems.
• For A angulation you should have to push your
  hand deep into the upholstery covering whereas
  for the B angulation you should be able to reach
  under without pushing down.

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DEALING WITH ROTATIONS

• Rotations can be very difficult to reduce.
• If dealing with a large rotation rotate the head
  ever so slightly so as to rest the malar on the
  headpiece ( for posterior rotations). This will
  provide a resistance to stop the head rotating
  allow more of the forces to effectively move the
  atlas.
• Another idea is to take an x-ray film eraser (
  still in the plastic) use it as a wedge to
  create the same effect. This works better than
  the above for anterior rotations.
• Also remember that with large lower angle in
  Basic Type Ones ( greater than 5 degrees) to pre
  stress. The shoulder should be moved down no more
  than an inch.

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• The more skilled you become, the more you
  appreciate the importance of skillful headpiece
  placement.
• you increasingly appreciate the sheer
  brilliance of the mastoid headpiece what it can
  do for you