The Sutural System of the Cranium

The physiological nature of the suture determines the type of motion in which it participates, and what it will allow. Understanding the nature of the suture allows us to not only understand its movement, but how we can optimize the performance of the sutural system.

We know that the cranial bones have growth centers, some more than others. The sutural tissue is continuous with the periosteum of the skull and, eventually, the dural coverings of the brain and spinal cord. Sutures have a synovial and a fibrous capsule. They also have a vascular system and are innervated by neural tissue.

Most sutures are either serrated (saw-toothed in groove) for expansion and contraction, or squamosal (beveled and overlapping) for gliding and rotation. There are variations of these types of sutures. Sometimes both of these types of sutures will be part of the same suture; sometimes there are sutures with both qualities. The serrated sutures promote expansion and contraction of the skull during respiration (flexion extension). Examples are the maxillary/malar and the malar zygomatic sutures. The squamosal sutures allow for rotation (external/internal) respiratory motion, as in the temporal sphenoidal suture.

There also are key pivot points in cranial sutures, allowing opposing motions, expansion and rotation to operate in an efficient and synchronized fashion. An excellent example of this would be the pivot point in the occipital mastoid suture that allows for temporal (a paired bone) external internal flexion and extension.
Sutures of one cranial bone may overlap another bone and partially through the suture change, and then bevel the other way. An example of this is the coronal suture (parietal frontal). Interestingly, the coronal suture is also both a serrated and squamosal suture with rotational and expansive properties.

Below I have listed various sutures, the type of suturing, and the nature of their functional relationship. Also below are pictures of what is believed to be the direction that the cranial bones move. This cranial movement is thought to be inherent, rhythmic and spontaneous, and to have a direct influence on dural tissue and cerebral spinal fluid movement. You will note that these motions are consistent with the anatomical nature of the various sutures:

1. Coronal suture (parietal/frontal suture) -- both a serrated and squamosal suture with overlapping and expansion properties. Just lateral to the bregma, the frontal overlap the parietal. There is a change at about one-third of the distance from the bregma where the parietal overlap the frontals.

    

2. Lambdoidal suture (parietal/occipital suture) -- both a serrated and a squamosal suture with overlapping and expansion properties. Just lateral to the lambda the occipitals overlap the parietal. There is a change of about one-half of the distance from the lambda where the parietal overlap the occiput.

    

3. Occipital/mastoid suture -- From the lateral-most part of the lambdoidal suture as you go inferior, the mastoid overlaps the occiput until the mastoid goes anterior/internal, then the occiput overlaps the mastoid.

    

4. Sagittal suture (interparietal suture) -- A serrated and dentated suture allows for motion but also allows for great resistance.

    

5. Temporal/parietal suture (squamosal suture) -- The temporal suture overlaps the parietal, especially at the most superior point along the suture up to the posterior inferior border of the parietal, and the mastoid portion of the temporal where it is serrated.

    

6. The sphenoid/frontal and sphenoid/parietal are the squamosal, with the sphenoid overlapping both the frontal and parietal, allowing for gliding movements.

    

7. The temporal/sphenoidal suture is both squamosal with temporal overlapping the sphenoid at its superior half, and serrated in the lower half.

    

8. The intermaxillary suture functions as a plain suture, strong, and tough but capable of lateral expansion.

    

9. The malar/temporal zygomatic suture is deeply serrated, allowing for expansion and motion.

    

10. The malar/sphenoidal suture is a squamosal suture with the sphenoid overlapping the malar.

     

11. The malar/maxillary suture is serrated but overlapping, with the maxillary bone overlapping the malar laterally and the malar overlapping the maxillary bone, medially allowing for significant movement.

As you can see, the nature of each of these sutures allows for specific movements within a controlled direction.

In closing, keep in mind that facial and vault bones (parietal, frontal, and the squamosal portions of the temporal and occiput) develop from membranous tissue, are extremely pliable and continuously remodeling to meet the functional demand of the key organs of the cranial facial complex (respiratory organs, ears, eyes, teeth, and the brain).

References

1. Walther D. Applied Kinesiology: Head, Neck, and Jaw Pain and Dysfunction: the Stomatognathic System, vol.2 Pueblo, CO: Systems DC, 1983.

    

2. DeJarnette B. Sacral occipital technic. Nebraska City, NB: MB DeJarnette, 1984.

    

3. Upledger DO and Vredevoogd J. Craniosacral Therapy. Chicago: Eastland Press, 1983.