Credit for this technique goes to Dr. Mariano Rocabado, from Santiago, Chile. I think it's quite unfortunate that he is known for his so called "6x6" home exercise program for patients with TMD. Many students and clinicians think that is the only thing he does, much like they think McKenzie only does extensions.
Rocabado's caseload is primarily TMD, but he is a manual therapist first and foremost. One of the best I've ever trained with. He noticed that some patients were not responding to the typical OA gapping techniques and the HEP of deep cervical flexor retraining and postural correction nodding exercises did not relieve their HA and/or cervical pain. Upon saggital x-ray view, these patients had an atlus that was adhered to the occiput both in neutral and in flexion, with the gapping occurring at AA instead of OA. This decreases subcranial space, is palpably less and tender to touch. This in turn leads to bony and soft tissue entrapment of greater occipital nerve causing radiating HA into the frontal and temporal region. Radiating complaints may also refer to the upper traps.
He devised a technique that involves A LOT of A/P shear through the frontal cranium. Mobilization hand is on the occiput, stabilization hand grasps C2, and not C1. The shear stretches the rectus capitus posterior minor, which is thought to be adhered and limiting the OA nod. Mobilizing UE shoulder's softest anterior part goes on the patient's forward. You stand to the side opposite your mobilizing arm.
The shear I estimate is at least 30-40# and is done by dropping your weight onto their forehead. I do this first to make sure the patient is ok with it. The distraction is performed by pulling on the occiput very hard to gap OA and roll up into cranial forward bending. Stabilization is on posterior C2. When the distraction is performed, you INCREASE the shear to prevent cervical forward bending, and isolate cranial forward bending. This is a pressure on/pressure off type mobilization and would be a lot to do as a sustained hold or grade 4. 2-3 sets of 6 reps are performed. It is normal for the patient to have difficulty breathing at end range.
This not only improves OA forward bending, but can relieve HA, and cervical pain. Rocabado even has x-ray proof after using this technique of before and after a few weeks of this plus postural correction, cervical retraction and deep cervical flexor exercises. The patients have increased subcranial space and gapping at OA in flexion. That's some EBM for you!
Btw, a patient of mine several years ago nicknamed this technique the skull-crusher, and it's stuck ever since (but I don't document it that)