Pettibon Spinal Biomechanics Proof

 We have taken the same cervical spine and put it in three different positions to measure their mechanical advantage.  The two forces of resistance used for all three positions include a 10 lb. head weight and an anterior weight of 3 lbs.  The pull of effort was determined to be the interspinalis for all three positions.

	Normal Neck	Straight/Military  Neck	Reverse Curve  Neck
Total Force of Effort of Interspinalis:
	54 lbs.	85 lbs.	89 lbs.
Total Shear:
	23 lbs.	10.5 lbs.	24.5 lbs.
Total Compression:
	123 lbs.	161 lbs.	163 lbs.
Direction of shear found at each individual joint:
C2-C3	4 lbs. posterior	2 lbs. anterior	4 lbs. anterior
C3-C4	5 lbs. posterior	0	.5 lbs. posterior
C4-C5	2 lbs. anterior	.5 lbs. posterior	3 lbs. posterior
C5-C6	2 lbs. anterior	4 lbs. posterior	6 lbs. posterior
C6-C7	4 lbs. anterior	2 lbs. posterior	5 lbs. posterior
C7-T1	6 lbs. anterior	2 lbs. posterior	6 lbs. posterior

 Initial impression:

The Pettibon theory of spinal correction would appear to be mechanically proven when moving from the reverse curve neck into the more military or straight neck.  The total force of effort, total compression and total shear created  would favor the cervical spine in the more military type posture (note - all shear is in the same direction).

Moving from the military towards the more desired curved neck presents complications.  Total force of effort and total compression created definitely favors the curved neck over the military neck.  Shear presents a different matter.  Shear is more than doubled in the curved neck and is in the opposite direction except at the C3-C4 joint.

Anterior shear would be stabilized the cartilaginous surfaces of the articular facets.  If the facets exhibited advanced degenerative conditions or sustained a recent injury (i.e., auto accident), immediate adaptation that would require the facets to sustain continual force in the upright position may be contraindicated.  If the facets are healthy, mechanically it appears that the curved neck posture would present the overall most favorable mechanical advantage that the body would want to adapt.

It appears at this time that preliminary mechanical proofs validate Pettibon's head weighting theory, however, we would recommend more mechanical proofs of different cervical spines be performed with empirical studies.