Cranial Rhythmic Impulse
10–14 cycles per minute (decreased in depression/fatigue)
SBS Torsion Axes
1 AP axis (named for high greater wing of sphenoid)
SBS Sidebending-Rotation
1 AP axis + 2 vertical axes (named for side of fullness)
Compression Strain
Head feels like a bowling ball / solid rock; CRI abolished
The 5 Core Components of the Primary Respiratory Mechanism
Described by William G. Sutherland, DO, the PRM consists of five interrelated rhythmic phenomena:
1. Inherent Motility of the Brain and Spinal Cord
A slow, subtle biphasic pulsation where the CNS coils and uncoils during embryologic and ongoing life.
2. Fluctuation of the Cerebrospinal Fluid (CSF)
Hydrodynamic tide fluctuating through the ventricles and subarachnoid space.
3. Mobility of Intracranial and Intraspinal Membranes (RTM)
The reciprocal tension membrane (falx cerebri, tentorium cerebelli, and spinal dura extending to S2).
4. Articular Mobility of the Cranial Bones
Bones with paired sutures undergo external rotation during flexion; midline bones (sphenoid, occiput, ethmoid, vomer) undergo flexion.
5. Involuntary Mobility of the Sacrum Between the Ilii
Sacral base counternutates (moves posterior) around the superior transverse axis during cranial flexion/inhalation.
Sphenobasilar Synchondrosis (SBS) Strain Patterns Matrix
SBS strains result from birth molding, trauma, or intrinsic tension. They are classified into physiologic vs non-physiologic patterns:
| Strain Pattern | Axes of Motion | Sphenoid vs Occiput Motion | Clinical Presentation / Vault Feel |
|---|---|---|---|
| Flexion / Extension | 2 Transverse axes | Same plane opposite rotation | Flexion: broad/short head; Extension: long/narrow head |
| Torsion (Physiologic) | 1 AP axis | Rotate in opposite directions | Named for high greater wing of sphenoid (Index finger high) |
| Sidebending / Rotation (Physiologic) | 1 AP + 2 Vertical axes | Rotate same way on AP; opposite on vertical | Named for side of fullness/widening (fingers spread apart) |
| Vertical Strain (Non-physiologic) | 2 Transverse axes | Rotate in same direction | Superior: sphenoid base cephalad; Inferior: sphenoid base caudad |
| Lateral Strain (Non-physiologic) | 2 Vertical axes | Rotate in same direction | Head feels like a parallelogram |
| Compression | None | Bones driven together into SBS | Severely depressed CRI; bowling ball head |
High-Yield Cranial Techniques & Cranial Nerves
Key techniques frequently tested on COMLEX:
CV4 (Bulb decompression)
Physician encourages cranial extension and resists flexion until the 'still point' is reached. Indications: stimulate uterine contractions in delayed labor, induce relaxation, reduce fever.
Venous Sinus Drainage
Decongests cranium: Confluence of sinuses (inion), occipital sinus, marginal sinus, sagittal sinus.
V-Spread Technique
Separates restricted or impacted cranial sutures by sending fluid wave across the diameter of the skull.
Suckling Difficulties in Newborns
Compression of the hypoglossal canal (CN XII) or jugular foramen (CN IX, X) between the occiput and temporal bone causes poor suckling / latching in infants.
COMLEX / OMM Integration
NBOME High-Yield Correlate
Vault Hold Finger Placement
- Index finger: Greater wing of the sphenoid.
- Middle finger: Pre-auricular temporal bone (zygomatic process).
- Ring finger: Post-auricular temporal bone (mastoid process).
- Little finger: Squamous portion of the occiput.
- Middle finger: Pre-auricular temporal bone (zygomatic process).
- Ring finger: Post-auricular temporal bone (mastoid process).
- Little finger: Squamous portion of the occiput.
Board Traps & Common Distractors
- Absolute Contraindications to Cranial: Acute intracranial hemorrhage, skull fracture, intracranial aneurysm, severe acute head trauma with elevated ICP.