Importance of Head Position for CEPH X-ray

[Post bimax]

One thing I’ve been curious about since I first started having doubts about my bimax result is importance of head posture during the CEPH and its impact on surgical planning. Small variations in head posture presumably impact important readings like the angle the occlusal plane makes when intersecting the TVL. Because of this I figured maybe CEPHs are all normalized relative to some standard measure like the Frankfurt Horizontal.

Yesterday I asked one of Gunson’s surgical assistants about the importance of head position during the CEPH and she said head position is “one of the most important parts of surgical planning” and “affects everything”. The way I read that, tilting your head up or down during a CEPH can completely change the surgical plan and proposed movements. That makes me a little angry because the CEPHs for my surgery were outsourced to incompetent assistants at my ortho’s office. I had to return multiple times to retake the CEPHs because they kept CUTTING OFF parts of the jaw in the image. They finally got my full jaw in the image by having me ‘look up’ so my chin wasn’t cut off at the bottom.

TL/DR: pay very close attention to head position when getting your CEPHs.

[PloskoPlus]

How important is the TVL anyway? All the geometric relationships (angles, distances) of the cephalometric landmarks are invariant under head rotation.  Just like when you rotate a cardboard box, the corner angles are still 90 degrees.

My retrograde surgeon did no planing that I’m aware of. He had me staring at the sky in all the photos. The radiologist he sent me to also had me staring up. Wolford had me staring down at the floor. He did my traces by hand very quickly and using a ruler and a protractor established my occlusal plane to be about 15 degrees. When I showed the traces to my surgeon he denied that my op was steep and pointed at my (film!) X-ray where my head was pointed skyward and of course my OP looked flat because the teeth were parallel to the edge of the film.  For Gunson my ortho took more cephs in (AFAIR) more intermediate position - neither looking down, nor looking at the stars.  The ceph was run through Quickceph. Lo and behold the OP came out to be within .1 degree of what Wolford determined by hand.

I had surgery 5 years ago. I "trusted my surgeon" and didn't delve into cephalometrics. I was too shell-shocked by Wolford's analysis to want to look into it any further and just grew a beard to cover up.  I've recently started to look at cephalometrics again. My gut feeling now is that it all boils down to normalising the OP and the other angular relationships. Getting these into the normal range won't turn anyone into a model, but at least the face won't look "off". So many "great results" are simply a young person with a significant deformity that was corrected to the point that it no longer drew attention away from their great features.  But if you look closer they still look somewhat off.

[Post bimax]

How important is the TVL anyway? All the geometric relationships (angles, distances) of the cephalometric landmarks are invariant under head rotation.  Just like when you rotate a cardboard box, the corner angles are still 90 degrees.

I think in the arnett analysis the OP angle is measured against the TVL.  So in that case head position does affect the OP readout.

[kavan]

I think in the arnett analysis the OP angle is measured against the TVL.  So in that case head position does affect the OP readout.

With Arnett analysis, they want 2 ABSOLUTES and everything else RELATIVE to those 2 absolutes.

First absolute is the PLUMB LINE of GRAVITY which is an absolute vertical.

Second absolute is an absolute HORIZONT which is PERPENDICULAR to the vertical. An example of a horizont that is PERPENDICULAR to the plumb line of gravity is the FLOOR.

Head position: Not necessarily how you hold your head normally. But rather how you hold it when you are looking into the distance at a mirror where you see your own eyes; your eye level, your 'own horizon'. There is also should be a ceph stat or a vertical chain that shows the plumb line of gravity, true direction of gravity, absolute vertical for reference.

The Arnett 'TVL' is a matter of aesthetic preference. It's based on what would be considered 'attractive' rather than just the 'norm'. It is a vertical that they want to pass through near the end of your nose BONE and also through the nasio-labial junction where the base of your nose meets the labial ledge area.

Your Frankfurt horizontal might not be perpendicular to this TVL. If not, that's OK. Nobody SEES your FH anyway. What people look at is alignment RELATIVE to the line of gravity (absolute vertical) and the FLOOR (assume it means a flat plane perpendicular to absolute vertical.)

If you give them (Gunson) a ceph that you took ELSEWHERE, they will rotate it so the 'TVL' passes through the points they want it to pass through and they will use a horizont that is perpendicular to that. It might be a horizont parallel to the floor or your FH if it happens to be parallel to the floor.

In essence, Arnett analysis makes things RELATIVE to an absolute vertical and absolute horizont. The rest is where they want the rest of your face to go relative to their TVL.

I put up some links that borders on this topic on the educational section.

[Post bimax]

If you give them (Gunson) a ceph that you took ELSEWHERE, they will rotate it so the 'TVL' passes through the points they want it to pass through and they will use a horizont that is perpendicular to that. It might be a horizont parallel to the floor or your FH if it happens to be parallel to the floor.

Ah, ok that makes sense.  The way I read it was that the CEPH would be analyzed “as is” (i.e, not rotated) and the TVL would be a plumb line passing through a single chosen point, and that the horizontal used for analysis would be perpendicular to that. If the TVL passes through TWO chosen points, that makes more sense that the CEPH orientation is adjusted to that.

[kavan]

Ah, ok that makes sense.  The way I read it was that the CEPH would be analyzed “as is” (i.e, not rotated) and the TVL would be a plumb line passing through a single chosen point, and that the horizontal used for analysis would be perpendicular to that. If the TVL passes through TWO chosen points, that makes more sense that the CEPH orientation is adjusted to that.

Correct. TVL has to pass through 2 chosen points. If it just passes through one, then your head can be tipped any which way.

[Gadwins]

I'm sorry for asking , but I didn't quite get that: Is the head posture important during Ceph or not?

[Post bimax]

I'm sorry for asking , but I didn't quite get that: Is the head posture important during Ceph or not?

Well it will probably depend on what analysis is being used. For A&G, presumably any ceph can be normalized by rubbing the TVL through the 2 selected points.

However it’s probably a good idea to maintain a neutral head position during any CEPH as the surgical assistant still described it as “one of the most important parts of surgical planning”. She didn’t elaborate.

[april]

Did they have you position or do anything in a certain way? (look ahead in a mirror etc)

Speaking of head posture, I had a scan for VSP with a surgeon, and they had me lay down for the scan. I don't understand how being supine can give an accurate head position to plan off, at least for face / soft tissue. Gravity would majorly change things.

[Post bimax]

Did they have you position or do anything in a certain way? (look ahead in a mirror etc)

Speaking of head posture, I had a scan for VSP with a surgeon, and they had me lay down for the scan. I don't understand how being supine can give an accurate head position to plan off, at least for face / soft tissue. Gravity would majorly change things.

They had me sit up straight and actually and a strap on my head to keep it still.  There was a mirror directly in front of me and a small figure on top (it was a toy or something) which they had me focus on.  I would say the figure was above eye level, but my head was not inclined to look upwards.

[PloskoPlus]

They had me sit up straight and actually and a strap on my head to keep it still.  There was a mirror directly in front of me and a small figure on top (it was a toy or something) which they had me focus on.  I would say the figure was above eye level, but my head was not inclined to look upwards.

Supposedly the neutral position is you looking into the eyes of your reflection.

[Post bimax]

Another possible method of CEPH orientation is to overlay the CEPH onto the clinical photographs taken during the consultation. In this method, head position during the photographs is the critical component as the photographs are used to orient the CEPH. Here is a demonstration:

https://youtu.be/4C3NHH72GIs