**13. Anterior approaches**

The most common indication historically for anterior approach to the craniocervical junction in rheumatoid patients was to perform a transoral odontoidectomy in cases of brainstem

Surgical Considerations of Rheumatoid Disease

C1/C2 motion segment.

away from the nerve root and vertebral artery.

degrees lateral in a rostrocaudal plane parallel to the facet joint.

Involving the Craniocervical Junction and Atlantoaxial Vertebrae 295

subaxial spine be relatively intact, and the subluxation be confined to the atlantoaxial joint, then we advocate simply performing a single level fusion. Avoiding including the very heavy skull and inferior subaxial levels will accomplish the dual goals of eliminating atlantoaxial subluxation, whilst also avoiding the creation of a very large moment arm about the fusion endpoint. If fixation to the skull is necessary we may extend the subaxial fixation as far as C4, but any longer fixation mandates extension of the fixation to T2. An intermediate level of fixation will produce a large moment arm with almost certain failure of the construct at its lower end. Our own series of 37 consecutive rheumatoid patients, with a minimum follow-up of 7 years post transarticular screw placement for atlantoaxial subluxation, demonstrated a 90% success rate in relief of neck pain and occipital neuralgia symptoms (Nagaria et al 2009). In our case series we defined "success" as at least a 50% reduction in the VAS. Both the Myelopathy Disability Indices and the Ranawat myelopathy score showed significant postoperative improvement. Bony fusion and stability was noted in 97% of cases on follow-up CT imaging and flexion/extension radiograph views of the

Though described initially by Roy-Camille slightly more than thirty years ago (Nagaria et al 2009), lateral mass screws have been the posterior fixation method of choice for the majority of spine surgeons for the past 20 years. Lateral mass fixation has the advantage over wiring or laminar screw techniques in that it may be used in conjunction with laminectomies or laminoplasties. A disadvantage is the proximity of the vertebral artery, the exiting spinal nerve root, and indeed the cord itself. In the original description, Roy Camille proposed an entry point in the middle of the lateral mass, and a drill/screw trajectory 10 degrees lateral from the parasagittal plane. In an average patient, a screw length of 14-16mm will achieve the bicortical purchase so important in these commonly osteoporotic patients. A number of variations on the concept, involving slightly different entry points and trajectories have been described, but the end-results are biomechanically broadly similar (McKibbin 1979, Xu et al 1998), and all techniques have at their core an emphasis on placing the screw trajectory

The Magerl technique describes the entry point as being 1mm medial to the centre of the lateral mass, and then angling the drill 20 degrees cephalad and 30 lateral trajectory. The vertebral artery usually lies anterior to the longitudinal depression or valley found in all cervical vertebrae between the laminae and lateral masses. Placing your entry point medial to the centre point of the lateral mass will lessen the risk of encountering the vertebral artery and nerve roots, whilst also maximising your screw length, thereby increasing the overall stability of your construct. Further variations of this original technique include the Anderson technique with entry point also 1mm medial to the mid-point and trajectory 10

Our lateral mass screw placement and trajectory is slightly different to these previously described techniques, with our focus being on achieving the longest possible bicortical screw placement through the lateral mass, whilst avoiding the nerve root or vertebral artery. To this end, we make our entry point at least 3 mm medial to the lateral mass midpoint, commonly along the lamina-lateral mass junction "valley", and then steeply angle laterally and caudally at angles of 30 degrees and 45 degrees respectively. Resting the drill guide on the spinous process of the inferior vertebra is a reasonable rule-of-thumb for the required trajectory (Varrey et al 2004), though in deformed rheumatoid patients especially this rule may not be completely reliable. In our experience it is often necessary to remove the tops of the spinous processes to achieve the required "back-and-out" drill slant. Previous

deformity caused by a fixed kyphotic deformity. Recent authors have published their series demonstrating that such an approach is not necessary if pre-operative traction is successful in reducing the kyphosis, given that the pannus causing the deformity resolves after a posterior immobilisation procedure (Martin M. et al 2010, Nagaria et al 2009). We reserve odontoidectomy for such cases of failed reduction with traction, concentrating on eliminating the medullary kink through resection of the odontoid itself, the body of C2 and a portion of the clivus, if necessary. Our practice is to confirm adequate medullary decompression with a post-operative MRI, before proceeding to a posterior stabilisation as a second procedure. Rheumatoid patients unfortunately are often unsuitable for this transoral approach to such ventral pathologies, due to an inability to open their mouths the required minimum of 2.5cm, or perhaps due to a fixed flexion deformity of their unstable cervical spine precluding adequate surgical access. Advantages of this approach include the presence of pannus usually being within 1.5cm of the midline (Grob et al 1997). The preparatory work and initial steps involving adequate neck extension in traction, use of Crockard transoral retractors to minimise swelling of tongue and lips, along with the midline posterior pharyngeal incision are described elsewhere (Fessler & Sekhar 2006). We often use a posterior pharyngeal flap allowing for greater exposure and less mucosal trauma from retraction.

A few salient anatomical points related specifically to removal of the rheumatoid pannus are warranted however. Direct incision over the tubercle of the atlas is vital as a first step to avoid straying off the midline, and placing neighbouring neural and vascular structures at significant risk. Once the anterior arch of C1 is removed, we dissect laterally to fully identify the borders of the Peg prior to beginning removal. In this way anatomical awareness is maintained throughout the procedure. Many authors advocate separating the peg inferiorly and delivering the upper end by pulling the, disarticulated, inferior end out, towards the surgeon. However we think that this practice is potentially dangerous with the tendency for the superior end of the peg to be displaced posteriorly into the medullary tissue during the manoeuvre. Our practice is to directly expose the upper end of the peg so it may be immobilised prior to any extraction manoeuvre.

Other authors stress the importance of closing the pharyngeal structures in 2 layers (Crockard et al 1986). We have found this almost impossible to achieve, due to the poor quality of the mucosa in these patients, particularly after prolonger retraction. We have routinely closed the posterior pharyngeal mucosa in a single layer without complication.

### **14. Subaxial instability & lateral mass screws**

Inclusion of subaxial points of fixation as part of an occipitocervical or atlantoaxial fusion may be required depending on the individual case. Post-operative follow-up is of the utmost importance in rheumatoid patients. Nowhere is this demonstrated more readily than in severe rheumatoid patients who have undergone craniocervical fusions involving only the atlas and axis. Such constructs whilst immobilising the spine at the upper motion segments, will accentuate the stresses experienced in the subaxial levels, and accelerated adjacent level breakdown may be seen (Smith et al. 1972). The ligamentous laxity so commonly seen in these patients, allied to uncovertebral joint synovitis, further promotes a rapid degenerative process. Due to this tendency we advocate extending the level of fusion to the upper thoracic spine. Our practice is to extend the construct to T2 at least if we encounter a cervical spine that has undergone significant degenerative change; should the

deformity caused by a fixed kyphotic deformity. Recent authors have published their series demonstrating that such an approach is not necessary if pre-operative traction is successful in reducing the kyphosis, given that the pannus causing the deformity resolves after a posterior immobilisation procedure (Martin M. et al 2010, Nagaria et al 2009). We reserve odontoidectomy for such cases of failed reduction with traction, concentrating on eliminating the medullary kink through resection of the odontoid itself, the body of C2 and a portion of the clivus, if necessary. Our practice is to confirm adequate medullary decompression with a post-operative MRI, before proceeding to a posterior stabilisation as a second procedure. Rheumatoid patients unfortunately are often unsuitable for this transoral approach to such ventral pathologies, due to an inability to open their mouths the required minimum of 2.5cm, or perhaps due to a fixed flexion deformity of their unstable cervical spine precluding adequate surgical access. Advantages of this approach include the presence of pannus usually being within 1.5cm of the midline (Grob et al 1997). The preparatory work and initial steps involving adequate neck extension in traction, use of Crockard transoral retractors to minimise swelling of tongue and lips, along with the midline posterior pharyngeal incision are described elsewhere (Fessler & Sekhar 2006). We often use a posterior pharyngeal flap allowing for greater exposure and less mucosal trauma

A few salient anatomical points related specifically to removal of the rheumatoid pannus are warranted however. Direct incision over the tubercle of the atlas is vital as a first step to avoid straying off the midline, and placing neighbouring neural and vascular structures at significant risk. Once the anterior arch of C1 is removed, we dissect laterally to fully identify the borders of the Peg prior to beginning removal. In this way anatomical awareness is maintained throughout the procedure. Many authors advocate separating the peg inferiorly and delivering the upper end by pulling the, disarticulated, inferior end out, towards the surgeon. However we think that this practice is potentially dangerous with the tendency for the superior end of the peg to be displaced posteriorly into the medullary tissue during the manoeuvre. Our practice is to directly expose the upper end of the peg so it may be

Other authors stress the importance of closing the pharyngeal structures in 2 layers (Crockard et al 1986). We have found this almost impossible to achieve, due to the poor quality of the mucosa in these patients, particularly after prolonger retraction. We have routinely closed the posterior pharyngeal mucosa in a single layer without complication.

Inclusion of subaxial points of fixation as part of an occipitocervical or atlantoaxial fusion may be required depending on the individual case. Post-operative follow-up is of the utmost importance in rheumatoid patients. Nowhere is this demonstrated more readily than in severe rheumatoid patients who have undergone craniocervical fusions involving only the atlas and axis. Such constructs whilst immobilising the spine at the upper motion segments, will accentuate the stresses experienced in the subaxial levels, and accelerated adjacent level breakdown may be seen (Smith et al. 1972). The ligamentous laxity so commonly seen in these patients, allied to uncovertebral joint synovitis, further promotes a rapid degenerative process. Due to this tendency we advocate extending the level of fusion to the upper thoracic spine. Our practice is to extend the construct to T2 at least if we encounter a cervical spine that has undergone significant degenerative change; should the

from retraction.

immobilised prior to any extraction manoeuvre.

**14. Subaxial instability & lateral mass screws** 

subaxial spine be relatively intact, and the subluxation be confined to the atlantoaxial joint, then we advocate simply performing a single level fusion. Avoiding including the very heavy skull and inferior subaxial levels will accomplish the dual goals of eliminating atlantoaxial subluxation, whilst also avoiding the creation of a very large moment arm about the fusion endpoint. If fixation to the skull is necessary we may extend the subaxial fixation as far as C4, but any longer fixation mandates extension of the fixation to T2. An intermediate level of fixation will produce a large moment arm with almost certain failure of the construct at its lower end. Our own series of 37 consecutive rheumatoid patients, with a minimum follow-up of 7 years post transarticular screw placement for atlantoaxial subluxation, demonstrated a 90% success rate in relief of neck pain and occipital neuralgia symptoms (Nagaria et al 2009). In our case series we defined "success" as at least a 50% reduction in the VAS. Both the Myelopathy Disability Indices and the Ranawat myelopathy score showed significant postoperative improvement. Bony fusion and stability was noted in 97% of cases on follow-up CT imaging and flexion/extension radiograph views of the C1/C2 motion segment.

Though described initially by Roy-Camille slightly more than thirty years ago (Nagaria et al 2009), lateral mass screws have been the posterior fixation method of choice for the majority of spine surgeons for the past 20 years. Lateral mass fixation has the advantage over wiring or laminar screw techniques in that it may be used in conjunction with laminectomies or laminoplasties. A disadvantage is the proximity of the vertebral artery, the exiting spinal nerve root, and indeed the cord itself. In the original description, Roy Camille proposed an entry point in the middle of the lateral mass, and a drill/screw trajectory 10 degrees lateral from the parasagittal plane. In an average patient, a screw length of 14-16mm will achieve the bicortical purchase so important in these commonly osteoporotic patients. A number of variations on the concept, involving slightly different entry points and trajectories have been described, but the end-results are biomechanically broadly similar (McKibbin 1979, Xu et al 1998), and all techniques have at their core an emphasis on placing the screw trajectory away from the nerve root and vertebral artery.

The Magerl technique describes the entry point as being 1mm medial to the centre of the lateral mass, and then angling the drill 20 degrees cephalad and 30 lateral trajectory. The vertebral artery usually lies anterior to the longitudinal depression or valley found in all cervical vertebrae between the laminae and lateral masses. Placing your entry point medial to the centre point of the lateral mass will lessen the risk of encountering the vertebral artery and nerve roots, whilst also maximising your screw length, thereby increasing the overall stability of your construct. Further variations of this original technique include the Anderson technique with entry point also 1mm medial to the mid-point and trajectory 10 degrees lateral in a rostrocaudal plane parallel to the facet joint.

Our lateral mass screw placement and trajectory is slightly different to these previously described techniques, with our focus being on achieving the longest possible bicortical screw placement through the lateral mass, whilst avoiding the nerve root or vertebral artery. To this end, we make our entry point at least 3 mm medial to the lateral mass midpoint, commonly along the lamina-lateral mass junction "valley", and then steeply angle laterally and caudally at angles of 30 degrees and 45 degrees respectively. Resting the drill guide on the spinous process of the inferior vertebra is a reasonable rule-of-thumb for the required trajectory (Varrey et al 2004), though in deformed rheumatoid patients especially this rule may not be completely reliable. In our experience it is often necessary to remove the tops of the spinous processes to achieve the required "back-and-out" drill slant. Previous

Surgical Considerations of Rheumatoid Disease

a safe solid pain-free end-result is to be achieved.

*Of Rheumatology. 19(9), 1364 – 1370.* 

*Clinical Biomechanics 13(9), 633 – 648.*

Anzhsn (2011) PediGuard™ Available from:

and plate-rod systems. *Spine 24(14), 1425 – 1434.* 

http://www.euroscan.org.uk/technologies/technology/view/1643

arthritis. *Annals of the Rheumatic Diseases 60 (5), 448 – 452.*

analysis. *Seminars in Arthritis & Rheumatism 19(4), 209 – 223.* 

**16. Conclusion** 

**17. References** 

*222-22.*

*1297.*

*17(2), 134 – 137.*

Involving the Craniocervical Junction and Atlantoaxial Vertebrae 297

developing a significant neurological morbidity. Our practice when placing pedicle screws in such patients is to utilise the Pediguard™, a device which doubles both as a hand-held awl and which also detects changes in electrical conductance at the device tip. Variation of conductivity occurs when passing between different media, such as exiting the osseous pedicle into surrounding soft-tissue, as occurs during an iatrogenic pedicle perforation. Our series demonstrated a sensitivity of >98% in detecting breaches, more than twice the rate reported by surgeons performing the same surgeries (Bolger et al 2007, Anzhsn 2011).

Rheumatoid arthritis affecting the craniovertebral junction and subaxial cervical spine remains a challenging surgical entity despite recent technological advances. Such cases need a pre-operative assessment by a multi-disciplinary team to ensure adequate medical optimisation prior to such invasive procedures, thereby limiting the risk of post-procedure medical deterioration. Symptomatic instability may require instrumentation, and success in such cases depends on the specialist knowledge of the unique altered bone morphology and the plethora of traversing neural and vascular structures. An appreciation of the biomechanical forces which instrumented constructs in this area experience is mandatory if

Abhilash J. et al (2002) Influence of steroids and methotrexate on wound complications after elective rheumatoid hand and wrist surgery. *Journal Hand Surgery 27(3), 449 – 455.*  Abumi K. et al (1999) Posterior occipitocervical reconstruction using cervical pedicle screws

Agarwal A. (1992) Recurrence of cervical spine instability in rheumatoid arthritis following

Aryon H.E. et al (2008) Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2

Assalt K.M. et al (2001) Outcome of cervical spine surgery in patients with rheumatoid

Baer A. (1990) The pathogenesis of anemia in rheumatoid arthritis: A clinical and laboratory

Bland J.H. (1990) Rheumatoid subluxation of the cervical spine. *The Journal Of Rheumatology* 

Boden S. et al (1993) Rheumatoid arthritis of the cervical spine. A long-term analysis with

Bogduk N. & Mercer S. (2000) Biomechanics of the cervical spine. I: Normal kinematics.

predictors of paralysis and recovery. *Journal of Bone and Joint Surgery 75(9), 1282 –* 

previous fusion: can disease progression be prevented by early surgery? *The Journal* 

pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques. *Journal of Neurosurgery: Spine - 8(3),* 

biomechanical studies have shown the more laterally divergent screws of the Magerl technique to have greater pull-out strength compared with the 10 degree Roy-Camille screw (Chin et al 2006), and we believe that our own variation on this with increased screw length at least partly accounts for our success in achieving fusion despite significant comorbidities (Heller et al 1991).

Inclusion of the C7 lateral mass may be required in a minority of cases. In such instances the surgeon's task is eased somewhat by the absence of the vertebral artery from the vertebral foramen, but it must be borne in mind that the C7 lateral mass is the smallest of all in the cervical spine. For this reason placement of a C7 pedicle screw with a 30 degree medial and perpendicular rostrocaudal trajectory is our usual practice. Should the occiput be included in such constructs however we advocate inclusion of at least T1 and T2 in the construct due to the dangers (screw pull-out and kyphosis) of stopping such a large moment arm at a transition junction. Careful review of 3D CT cervical spine pre-operatively will allow the surgeon to gauge pedicle size, and also recognise any aberrant vertebral artery anatomy.
