by Erik Dalton, PhD
A positive test for a head-forward posture requires that the zygomatic arch under the eye be more than 3 centimeters forward of the sternoclavicular joint. Clients presenting with head-forward postures are vulnerable to increased stress not only in the neck but the jaw as well. When assessing and correcting this common postural pattern, therapists should recall that the jaw functions separately from the cranium. Embryologically, the jaw develops from visceral myotomes…not cranial.
In those with forward head postures, the head and neck moves forward in the sagittal plane causing the brain to backward-bend occiput on atlas. This remarkable proprioceptive reflex (Law of Righting) will cock the head back to level the eyes against the horizon even if it means ravaging the neck.
Regrettably, prolonged head hyperextension causes sustained isometric contraction in the sensitive suboccipital muscles. The suboccipitals actually have no Golgi tendon organs (GTOs) as they attach to the cranium but are loaded instead with an abundant supply of type 3 mechanoreceptors. Type 3 (Golgi end organs) usually found in ligaments, perform identical functions as the tendon organs except they do not respond to contraction by their synergistic stabilizers (muscles performing the same action a given joint.) Therefore, Golgi end organs allow the suboccipitals to maintain proprioceptive balance while other muscles attaching to the occipital ridge continue performing their particular duties.
Sustained isometric contraction in the capital extensor muscles places the entire nervous system in a heightened state of alert. With the head in a forward position, passive tensile forces develop in the hyoid and digastric muscles causing them to shorten, tug on the mandible and translate the jaw posteriorly and inferiorly. Jaw retrusion develops as these tight muscles hold the jaw back as the head translates forward. The temporalis and masseter muscles must now co-contract so the mouth can be kept closed. Prolonged temporalis and masseter contraction promotes abnormal mandibular positioning and disc compression at the temporomandibular joint (TMJ).