The Study: Standing sagittal alignment of the whole axial skeleton with reference to the gravity line in humans.
a. The chain of balance for the standing position starts at the feet.
b. It then proceeds up through the spine to the head in order to have balance with minimum muscle activity.
c. However, we do not fully understand all “the three dimensional (3D) orientation of all bony elements in relation to the gravity line (GL).”
d. The authors designed a study to look at “the standing sagittal alignment of whole axial skeletons in reference to the GL…”
e. The study used an EOS 3-D x-ray* and subjects were placed on a force plate during the imaging studies.
Editor’s Note: *In previous articles, we have touched on the use of the EOS 3D imaging system which uses slot scanning technology to produce high quality, 3D radiographs while substantially reducing radiation exposure. The technology is growing in use particularly when there is a need for full body weight bearing imaging in conditions such as scoliosis, kyphosis, or other skeletal deformities. Doctors with an interest in postural correction/rehabilitation should begin familiarizing themselves with this valuable technology which is showing value in research as well as treatment.
f. The study looked at 136 healthy subjects with a mean age of 39.7 years.
g. A mirror was placed in the x-ray room so that subjects could use it to establish a horizontal gaze while being x-rayed.
h. Full body x rays were taken from the top of the head to the bottom of the feet.
i. The authors hypothesized that humans stand with alignment in the sagittal plane in order to have horizontal vision and that changes that may occur in one area as the person ages will be compensated for by changes in other areas in order to maintain this horizontal gaze.
j. The “cone of economy” is an important concept to understand from a biomechanical view point and is the “3-D orientation of all the boney elements in relation to the gravity line” with considerations as to the minimum expenditure of energy and/or minimum postural sway during upright posture.
k. The authors found that cervical lordosis, pelvic tilt, pelvic incidence, hip extension, knee flexion and ankle dorsiflexion all increased with age.
l. In other words, as aging tends to cause trunk stooping, the body compensates with increases in cervical lordosis, pelvic tilt and knee flexion.
m. The authors concluded that the main purpose of the increased cervical lordosis and pelvic tilt was to help the subject maintain horizontal gaze.
Increases in pelvic tilt, knee flexion and cervical lordosis in aging may well be compensatory postures to help the subject maintain a horizontal gaze.
I’m not convinced that the purpose of the compensation is mainly to maintain a horizontal gaze. The last time I walked, on something other than a flat surface, I noticed that I kept looking down so that I didn’t trip. I’m pretty sure there were way more uneven surfaces 10,000 years ago than there were flat surfaces. If you want to test this mechanism of horizontal gazing in terms of survival I suggest going to the Magic Kingdom over the Christmas vacation and seeing if maintaining a horizontal gaze allows you to avoid strollers the size of small battleships.
If you set up a study by having subjects start out with a horizontal gaze then you have effectively set that as the origin and you will see and relate everything to that in the study (i.e. you have set the standard regardless of whether or not the your reasoning is correct.). I would have preferred it if they were standing in their relaxed normal stance. However, the ability to be able to achieve a horizontal (and an inclined and a declined gaze) is important. What I think we can say is that when one part of the body stoops then another part tries to compensate and this compensation improves balance relative to gravity. As balance moves closer to the gravity line less muscle effort is needed to maintain an erect posture i.e. less energy usage and a more efficient cone of economy. So once again, alignment is important, gravity matters and the authors from the Spine Surgery Center and the Department of Orthopaedic Surgery in Nigata, Japan have contributed to our knowledge for those chiropractors willing to think beyond the mere adjusting of spines to improve segmental mobility. I thank them for their work.
Reviewer: Roger Coleman DC
Editor: Mark R. Payne DC
Reference: Hasegawa K, Okamoto M, Hatsushikano S, Shimoda H, Ono M, Homma T, Watanabe K. Standing sagittal alignment of the whole axial skeleton with reference to the gravity line in humans. J Anat. 2017 May;230(5):619-630. doi: 10.1111/joa.12586. Epub 2017 Jan 27.
Link to Abstract: https://www.ncbi.nlm.nih.gov/pubmed/28127750