**Surgical Considerations of Rheumatoid Disease Involving the Craniocervical Junction and Atlantoaxial Vertebrae**

T.M. Murphy, L. McEvoy and C. Bolger *Beaumont Hospital, Dublin, Ireland* 

## **1. Introduction**

274 Rheumatoid Arthritis – Etiology, Consequences and Co-Morbidities

Teigland, J., Ostensen, H., & Gudmundsen, T. E. (1990). Radiographic measurements of

19*,* No. 2, pp. 105-114.

occipito-atlanto-axial dislocation in rheumatoid arthritis. *Scand.J.Rheumatol.,* Vol.

Rheumatoid arthritis is a progressive systemic erosive inflammatory polyarthropathy causing symptoms both as a result of disease progression, (Zikow et al 2005, Gorter et al 2010, Klarenbeek at al 2010), and as result of medical management of the disease process itself (Haugeberg et al 2003). It affects synovial joints in 1% of the world's population (Matteson 2003) , with more than 50% of those affected experiencing involvement of the cervical spine (Cabot & Becker 1978, Yurube et al 2011, Garcia- Arias et al 2011) It is characterised by an erosive synovitis, causing destruction of the articular joint surfaces, joint capsules and supporting ligaments for the joints. The atlantoaxial joint is the most commonly affected (Dreyer et al 1999). Though the disease process can cause horrendous morphological change to the cervical joints, with concomitant changes to joint function and stability, neurological dysfunction is surprisingly uncommon. The importance of regular neurological assessment and rapid intervention lie in the rapid progression to disability with the onset of neurological deficits (Rana 1989), allied with a significantly increased mortality rate (Mikulowski et al 1975, Paus et al 2008).

Great strides in the development and evolution of spine surgery techniques and instrumentation have been made treating individuals with cervical and craniocervical junction dysfunction. The complexities encountered when approaching the craniocervical junction of a severe rheumatoid neck, and the anatomical variability of the neural and vascular structures that may be iatrogenically breached (Bruneau 2006) mandate the use of image guidance techniques and/or conductivity detection devices (Kelleher et al 2006) to limit intraoperative risk (Kotani et al 2003, Aryon et al 2008).

The vertebrae of the region most commonly affected by rheumatoid degenerative disease, namely the craniocervical junction and the atlantoaxial joints, have a very complex anatomical relationship with traversing nerves, vessels, and of course the spinal cord (Oliveira et al 1985), and an appreciation of the structure and function of the components of these joints (including how degenerative changes alter the kinematics and structural integrity) is integral to safe surgery in the region.

The most common causes for surgical review of the cervical spine of rheumatoid patients include basilar invagination, atlantoaxial instability and subaxial subluxation (Boden et al 1993). Despite an improvement in spine surgical techniques and technology, rheumatoid

Surgical Considerations of Rheumatoid Disease

**atlantoaxial joint** 

subluxations (Rahimi et al 2003).

rays, CT, and MR imaging.

Involving the Craniocervical Junction and Atlantoaxial Vertebrae 277

The most commonly used radiological screening tool in nonspecialist units are x-rays of the cervical spine in maximum flexion and extension. However, many cases of subluxation will

Computed tomography (CT) is vital when considering which surgical approach to use when fusing posteriorly with a rod and screw fixation. Anomalies such as anomalous courses of vertebral arteries, the presence of arcuate foramina, a small pars interarticularis of C2, or a small lateral mass of C1 can all be appreciated on review of 3D-reconstruction of contiguous axial images stretching from the inion to C4, with added benefit of being suitable for use also for neuronavigation-aided screw placement (Mayer 2005). Soft tissue windowing allows evaluation of pannus. CT is also the ideal imaging modality for evaluation of rotatory

Magneitic resonance imaging (MRI) is of particular use when reviewing patients with multilevel rheumatoid involvement or in evaluating cases of cranial settling. When compared with CT, MRI is more accurate in evaluating soft-tissue and pannus. It does however have serious limitations when attempting to evaluate bony anatomy. We have performed dynamic flexion MRIs in the past as suggested by some authors, but haven't found it to be of significantly more use than conventional static MRI (Reijnierse et al 2000) in the majority of cases. It may be suitable for a small number of cases where stability or compression is in doubt. In cases being considered for surgical intervention we advocate x-

No matter which modality is presented to the clinician, he/she must be aware of the various radiographic measurements used when determining cranial settling and atlantoaxial subluxation. However, these measurements are now largely of academic interest, having been replaced in day to day practice by the direct visualisation of the anatomical structures with MRI. Projection of the odontoid peg tip above McRae's Line is considered abnormal, as is projection of the odontoid peg tip more than 3mm past Chamberlain's line. A Ranawat's distance of less than 13mm is also suggestive of cranial settling (Smoker 1994). Whilst the anterior atlantodental interval has been shown to be of great use when assessing non-rheumatoid patients for the presence or absence of spinal cord compression, rheumatoid cases are quite different. In this group of patients the pannus surrounding the odontoid peg can be quite large, and use of the anterior atlantodental interval may in fact underestimate the amount of spinal cord compression. An atlantodental interval of greater than 10mm suggests an incompetent transverse ligament (Dickman et al 1996). The transverse ligament may be lax, as in rheumatoid patients, or may be breached as is more commonly seen in trauma cases (Dickman. et al 1991). The posterior atlantodental interval has been shown to be a greater predictor of space available for cord, and of severity of neurological dysfunction (Boden et al 1993). Posterior atlantodental intervals of 14mm or more are considered to be the lower limit of normal (Oda, et al 1995). Post-operative radiographic images should be interpreted in the

The ease of use and ready availability of MRI scanning to directly visualise the neural

setting of such radiographic and craniometric measurements.

elements has largely superseded these measurements.

**4. Radiological assessment of the rheumatoid craniocervical junction and** 

only reveal themselves on maximum pain-free flexion and extension views.

disease of the cervical spine remains a challenging opponent for the modern day spine surgeon. The challenge lies in both the poor general medical condition of most rheumatoid patients with cervical spine dysfunction (Skues & Welchew 1993), and the bone destruction and ligamentous laxity that make instrumentation difficult in all but the most specialists of practices. A predilection for developing post-operative infections also contributes to an understandable wariness on the part of non-specialist neurosurgical/orthopaedic surgeons of embarking on major instrumentation without having ready access to the necessary backup should complications arise (Lidgran 1973, Grennan et al 2001).
