SpineUniverse Case Study Library

C1-C2 Instability in Patient with Rheumatoid Arthritis


A 50-year-old female presents with a chief complaint of neck pain. The pain is in the base of the neck with radiation to bilateral posterior shoulders. It worsens with movement.

She denies numbness, tingling, weakness in extremities or difficulty with gait or bowel/bladder control.

She has a past medical history of rheumatoid arthritis. She has been treated for 15 years with oral steroids and is currently still using them.


 A physical exam reveals the following:

  • Awake, alert, oriented x3
  • Normal gait/station
  • Positive heel/toe/tandem walk
  • Motor exam 5/5 throughout bilateral upper and lower extremities
  • Equal and symmetric deep tendon reflexes in bilateral upper and lower extremities
  • Negative Hoffman’s sign bilaterally
  • Extremities are warm and well perfused

Prior Treatment

The patient has been on and continues to be on oral steroids for rheumatoid arthritis.

She has tried physical therapy, activity modification, and pain medication for her neck pain, but she has not found relief.

Pre-treatment Images

 Fig 1 An and Cha RA Instability Pre-op AP X-rayFigure 1:  Pre-operative AP x-ray


Fig 2 An Cha RA Instability Pre-op Sagittal X-rayFigure 2:  Pre-operative lateral x-ray


Fig 3 An Cha RA Instability Pre-op Flex-Ext X-raysFigure 3A and 3B:  Pre-operative flexion-extension x-rays.  Posterior atlanto-dens interval measurements:  flexion is 12 mm, and extension is 18 mm.


Fig 4 An Cha RA Instability Pre-op Sagittal MRIFigure 4:  Pre-operative sagittal MRI


Fig 5 An Cha RA Instability Pre-op Axial MRIsFigure 5A and 5B:  Pre-operative axial MRI scans through C1


Fig 6 An Cha RA Instability Pre-op Axial MRIs 2Figure 6A and 6B:  Pre-operative axial MRI scans through C2


Figures 7-10 are pre-operative sagittal CT scans.

Fig 7 An Cha RA Instability Pre-op Sagittal CT 1Figure 7


Fig 8 An Cha RA Instability Pre-op Sagittal CT 2Figure 8


Fig 9 An Cha RA Instability Pre-op Sagittal CT 3Figure 9


Fig 10 An Cha RA Instability Pre-op Sagittal CT 4Figure 10



The patient has os odontoideum with C1-C2 instability, in addition to rheumatoid arthritis.

Suggest Treatment

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Selected Treatment

The patient underwent a posterior C1-C2 fusion with instrumentation (C1 lateral mass, C2 pars) with modified Gallie-Brooks wiring with allograft.

The following slide summarizes research done on RA in the cervical spine and treatment recommendations.

Slide An Cha RA Instability


Intraoperative Image

 Fig 11 An Cha RA Instability Intraop PhotoFigure 11:  Intraoperative photo showing instrumentation

Post-treatment Images


Fig 12 An Cha RA Instability Post-op X-rayFigure 12:  Post-operative x-ray showing instrumentation


Fig 13 An Cha RA Instability Post-op Sagittal X-raysFigures 13A and 13B:  Post-operative sagittal x-rays



The patient is now 6 months post-op. She has complete relief of her pain in the neck region, and she has no new issues with weakness, numbness, balance, or bowel/bladder issues. She’s intact neurologically. Her incision is well-healed.

Case Discussion

This patient's diagnoses are rheumatoid arthritis (RA) and os odontoideum with C1-2 instability.

The indications for surgery for C1-C2 instability, caused by either RA or os odontoideum, are neurologic deficit, refractory neck pain, and radiographic evidence of significant instability. She had no neurologic compromise, but she did have neck pain and instability.

Boden's classic 1993 paper on RA of the cervical spine taught us that we should focus on the posterior atlanto-dental interval (PADI) rather than the anterior atlanto-dental interval (AADI), the parameter that most surgeons used prior to that study. The PADI is the same as the space available for the cord (SAC) and that measurement was found to be a better predictor of paralysis than the AADI. The PADI may be smaller when measured on an MRI than a plain radiograph because soft tissue (pannus) may narrow the SAC and this will only be seen on the MRI.

Boden and colleagues recommended checking an MRI in patients with neurological symptoms or when the PADI measures 14 mm on plain radiographs. Surgery is felt to be indicated for radiographic C1-C2 instability when the PADI on MRI is 13 mm or less.

The patient did not have much, if any, pannus formation from RA and she had no basilar invagination or subaxial instability. Basilar invagination (aka, cranial settling) should always be considered because it has an even worse prognosis for paralysis and sudden death than atlantoaxial instability and may require extending the fusion to the occiput. Subaxial instability is less common but, when present, requires extending the fusion lower, often into the upper thoracic spine.

This case is unusual because the patient had both RA and os odontoideum. The os odontoideum makes measuring the PADI problematic because the odontoid is a free ossicle. The pathology in this case is actually more consistent with instability from the os odontoideum than RA because of the lack of pannus and the fact that C1 is posteriorly subluxed relative to C2 (see CT). Posterior C1-C2 subluxation can be seen in patients with RA when the odontoid is eroded from synovitis or when it is fractured. Of course, her os odontoideum may represent a remote odontoid fracture with nonunion, but the appearance on CT looks like a classic os odontoideum.

Whether the instability is from her os odontoideum or RA, surgery is reasonable and a C1-C2 fusion is the appropriate procedure.

There are different ways to achieve a C1-C2 fusion. The original methods, Gallie or Brooks-Jenkins fusions, involved wiring autograft bone graft to the posterior elements of C1 and C2. More recently, C1-C2 transarticular screws and C1 lateral mass screws attached to C2 screws with rods have become popular techniques and excellent results have been reported. If wire constructs are used without supplementary screws or rods, a halo is required in RA to prevent pseudoarthrosis. Some surgeons wire allograft to the posterior elements, as was done in this case; other surgeons prefer autograft.  Some surgeons do not wire the graft when using screw constructs. However, biomechanical studies have demonstrated an advantage to the combination and it is this author’s preference to use as much fixation as possible in this challenging healing environment.

This patient had an excellent result, which is expected when surgery is done early. If surgery had been delayed until the patient had significant neurologic compromise, the morbidity would have been much greater and the neurologic deficit may have persisted. 

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