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Your Grabb Oakes Measurement: What Does It Mean?

The headaches, brainfog and balance problems has been progressive in nature and unresponsive to conservative care. After what seemed like endless consultations and examinations your chiropractor believes it is Craniocervical Instability.  During a surgical evaluation the MRI was reviewed, and different measurements were taken all of which was confusing. What is the Cranium? What is the Craniocervical Junction?  What is in the Craniocervical Junction?  What is the Grabb Oakes Measurement?  How is the Grabb Oakes Measurement determined? What is a normal Grabb Oakes Measurement?  What is its significance? Let’s dig in. 

Introduction

A Grabb Oakes measurement is a radiographic tool used in the evaluation of upper neck and Brain disorders. 

Upper Cervical Anatomy Tidbits

Below is some anatomy of the Cervical Spine.  Understanding it is central to understanding the Grabb Oakes Measurement.  

What is the Cranium? what is the Craniocervical junction

The Cranium Is your skull.  Otherwise, known as your noggin.  The Brain is contained and protected by the Cranium.  The Brain has many different parts.  The lowest part of the Brain is called the Brainstem.  It connects to spinal cord.  The Brainstem is responsible for vital functions of life such as breathing, heart rate, and blood pressure. 

What Is the Cervical Spine?

Your neck is also called the Cervical Spine.  It starts at the base of the skull and is composed of multiple structures which include bones, discs, facet joints, ligaments and tendons. The bones in the neck are also known as Vertebral bodies.  There are 7 Vertebral bodies in the neck that stacked upon one another.  They are numbered 1 through 7.  The letter C precedes each number indicating that we are referencing the Cervical Spine. C=cervical.  The top bone is the C1 and is also referred to as the Atlas. The lowest bone in the neck is the C7

What Is the Craniocervial Junction? 

The Craniocervical Junction is the area between the Skull and the Cervical spine. It consists of the bones that forms the base of the Skull,  the first two bones in the Spine, and the neural structures that pass from the brain down into the Cervical Spine. To learn more about the Craniocervial Junction please read my previous blog

What Is In the Craniocervical Junction?

The base of the Skull has a large opening at its base called the Foramen Magnum. Foramen in latin meanings opening.  Magnum means large.  So the Foramen Magnum is a large boney opening at the base of the Skull that allows important structures to pass through. The Brainstem is the lowest part of the brain.  It can also be called the Medulla.  It connects directly to the Spinal Cord. The Brainstem is protected and encircled by the Cerebral Spinal Fluid (CSF).  This is illustrated in the sagittal MRI of the Brain and neck shown below.  This is a side-view image of the anatomy.  The Brainstem is dark in color and located at the base of the Skull.  It connects directly with the Spinal Cord which is also dark in color.  In contrast, the Cerebral Spinal Fluid (CSF) is white in color and that provides an important layer of protection. The C2 bone lies in front of the Spinal Cord and CSF and is identified in white letters.  

How Is the Grabb Oakes Measurement Determined? 

A line is drawn from the front of the Foramen Magnum to the lowest posterior aspect of the C2 bone.  The front of the Foramen Magnum is also referred to as the Basion.  A second line is then created that is perpendicular to the first line and extends to the Dura.  The Dura is a protective layers that covers the Spinal Cord and Brain.  It is the black line that is immediately adjacent to the backside fo the C2 body.  The Gabb Oakes measurement is illustrated by the yellow line.  It is the distance between the intersection of the two lines and the Dura.  For a step by step guide on how to determine the Grabb Oakes Measurement please see my prior blog.

What Is a Normal Grabb Oakes Measurement? 

A normal Grabb Oakes Measurement in adults is 9mm or less (1).

What Is the Signficance of the Grabb Oakes Measurement? Metric of Brainstem Compression

The Grabb Oakes Measurement is a measure of the upper cervical canal and its contents.  Remember that the Brainstem and all the neural elements descend from the Brain through a boney hole at the base of the Skull called the Foramen magnum.  Like the plumbing in your house or apartment it is important to keep the pipes clear of any debris that can narrow or obstruct water flow.  The consequences of  an obstruction or narrowing of a water line can be signficant with backing up of water which ends up on the floor or reduced water pressure in the shower.  

So too in the Cervical Spine.  If the C2 bone is malpositoned or unstable, the Central Canal can be narrowed.  This can also occur if there is thickening of the capsule on the Dens which is called Pannus.  Narrowing of the Central Canal can cause irritation or compression of the Brainstem resulting in several neurologic symptoms depending upon the severity of the compression.   These symptoms include brainfog, dizziness, headaches, fatigue and neck pain.  Narrowing of Central Spinal Canal can also cause problems with the flow of Cerebral Spinal Fluid.  Cerebral Spinal Fluid is a column of fluid that surrounds and protects the Brain and Spinal Cord.   In some cases the fluid backs up causing increased pressure within the Skull.  This is referred to as Intracranial Hypertension. 

To learn more about the importance of the Grabb-Oakes Measurement please click on the video below:

Treatment Options for Abnormal Grabb Oakes Measurements

An increased Grabb Oakes Measurement can be due to congenital, degenerative or traumatic causes.  Congenital and degenerative causes typically require surgery. 

Trauma or laxity of the upper cervical ligaments can also cause an increased Grabb Oakes Measurement. In many of these cases,  a non surgical treatment option exists where the damaged Transverse Ligament is injected under x-ray guidance.  The treatment is called the PICL which stands for Percutaneous Implantation of Cervical Ligaments. The procedure is very demanding and only performed at the Centeno-Schultz Clinic in Broomfield Colorado.  To learn more about this groundbreaking procedure please click on the video below. 

In Conclusion 

  • The Grabb Oakes Measurement is a radiographic tool used in the evaluation of upper Neck and Brain disorders.
  • The Craniocervical Junction is the area between the skull and Cervical Spine.  It contains the neural structures that pass from the Brain into the Cervical Spine and includes the Brainstem.
  • The Grabb Oakes Measurement is obtained by drawing a line from the Basion to the inferior posterior aspect of C2.  A perpendicular line is then drawn to the Dura. The length of the latter line is the Grabb-Oakes Measurement.
  • A normal Grabb Oakes Measurement in adults is 9 mm or less.
  • The Grabb Oakes Measurement provides a metric of Brainstem compression.  A C2 bone that is malpositioned or unstable can cause narrowing of the Central Canal and potential compression of the Brainstem. Symptoms vary depending upon the severity of the narrowing and compression.
  • An increased Grabb Oakes Measurement can be caused by congenital, degenerative and traumatic causes. Congenital and degenerative causes typically require surgery.
  • Laxity of injury of the Upper Cervical ligaments can also cause an increased Grabb Oakes measurement.  
  • Percutaneous Implantation of Cervical Ligaments is a nonsurgical treatment utilizing Bone Marrow Concentrate which contains stem cells.

The physicians at the Centeno-Schultz Clinic are experts in the nonsurgical treatment of Upper Cervical injuries including Craniocervial Instability and Atlantoaxial Instability.  The Grabb Oakes Measurement is one of the many tools utilized in the evaluation of patients.  Treatment options include x-ray guided PRP and Bone Marrow Concentrate.

If you or a loved one have ongoing neck pain, headache, and dizziness that has not responded to conservative treatment, please schedule a telephone Candidacy discussion with a board-certified, fellowship-trained physician. At the Centeno-Schultz Clinic, we are experts in the evaluation and treatment of upper neck injuries.  From the comfort of your home or office learn what treatment options are available for you.

Related: “7 Criteria for Diagnosing Craniocerivcal Instability” by Dr. John Schultz


1. Henderson FC Sr, Francomano CA, Koby M, Tuchman K, Adcock J, Patel S. Cervical medullary syndrome secondary to craniocervical instability and ventral brainstem compression in hereditary hypermobility connective tissue disorders: 5-year follow-up after craniocervical reduction, fusion, and stabilization. Neurosurg Rev. 2019;42(4):915-936. doi:10.1007/s10143-018-01070-4

2.Tedeschi, Helder; Ghizoni, Enrico; Mathias, Roger N.; Fernandes, Yvens B.; Joaquim, Andrei F.;Batista, Ulysses C. (Apr 1, 2015). “Computed tomography evaluation of the normal craniocervical junction craniometry in 100 asymptomatic patients”. Neurosurgical Focus. 38 (4): E5.doi:10.3171/2015.1.FOCUS14642. ISSN 1092-0684.