**9. Pre-operative traction**

The practice in our unit for a number of years has been to initiate preoperative traction using an MRI compatible HALO ring (Oda et al 1991). This traction is then maintained during the surgical procedure to prevent the loss of valuable millimetres gained during the preceding days in traction, when the patient is being transferred to the operating table. Such millimetres may prove vital in cases of cranial settling and basilar invagination, in improving the degree of medullary compression. Should adequate reduction be possible with the traction, we proceed with a posterior-only decompression and fusion. Adequate and maintained reduction is successful in the majority of cases of rheumatoid atlantoaxial subluxation, as opposed to cases of basilar invagination with concurrent Chiari malformations (Caird & Bolger 2005). In cases of inadequate reduction, we believe our decision to proceed with an anterior odontoidectomy, and subsequent posterior stabilisation, is strengthened despite the slightly greater risks associated with such an approach. Placement of pre-operative tracheostomy and gastrostomy tubes facilitate healing of such anterior approach wounds, whilst allowing regular respiratory toilet and enhanced caloric intake, reducing risks of pneumonia or catabolism.

Rod and screw instrumentation is our favoured method of treating instability in the upper cervical spine. Techniques such as sublaminar wiring, loops or autologous grafting do not provide immediate stability, thereby mandating prolonged use of impractical HALO-vests or hard collars. A rapid return to mobilisation achievable through use of a variety of rod and screw arthrodises will optimise the chances of a full return to independent living in this vulnerable patient cohort.

The goal with all of the surgical techniques used to treat rheumatoid cervical disease is to restore or preserve neurologic function. The precise technique used by the surgeon to achieve this will depend both on the individual radiological findings and on surgeon preference.

#### **10. C1C2 Transarticular screws**

In cases of atlantoaxial subluxation, without evidence of cranial settling, we advocate stabilisation of the C1-C2 segment through the use of transarticular screws (Krauss et al 2010). Careful scrutiny of preoperative CT imaging will identify cases where such screw trajectories are dangerous or impossible, such as abnormal positioning of the transverse

Such disease-modifying agents are recommenced after a period of 12 weeks to allow the maximum bony fusion to occur around the arthrodesis. The one exception in the disease modifying drug group is glucocorticoids. Rheumatoid patients have commonly been receiving oral glucocorticoids as a adjunct to other agents for a few decades by the time surgical intervention is recommended. By such a stage the hypothalamic-pituitary-adrenal has been completely suppressed, placing them at risk of an Addisonnian crisis if such medications are not administered. A large bolus of steroids is usually administered at the same time as that of antibiotics, with "stress-doses" continued for 3 days post-operatively. Due to the severity of the subluxation and deformity seen in the spines of these patients, along with accompanying cricoarytenoid and temporomandibular arthritis (Chen et al 2005, Paulsen 2000), the anaesthetists fibreoptically place the endotracheal tube whilst the patient

The practice in our unit for a number of years has been to initiate preoperative traction using an MRI compatible HALO ring (Oda et al 1991). This traction is then maintained during the surgical procedure to prevent the loss of valuable millimetres gained during the preceding days in traction, when the patient is being transferred to the operating table. Such millimetres may prove vital in cases of cranial settling and basilar invagination, in improving the degree of medullary compression. Should adequate reduction be possible with the traction, we proceed with a posterior-only decompression and fusion. Adequate and maintained reduction is successful in the majority of cases of rheumatoid atlantoaxial subluxation, as opposed to cases of basilar invagination with concurrent Chiari malformations (Caird & Bolger 2005). In cases of inadequate reduction, we believe our decision to proceed with an anterior odontoidectomy, and subsequent posterior stabilisation, is strengthened despite the slightly greater risks associated with such an approach. Placement of pre-operative tracheostomy and gastrostomy tubes facilitate healing of such anterior approach wounds, whilst allowing regular respiratory toilet and enhanced

Rod and screw instrumentation is our favoured method of treating instability in the upper cervical spine. Techniques such as sublaminar wiring, loops or autologous grafting do not provide immediate stability, thereby mandating prolonged use of impractical HALO-vests or hard collars. A rapid return to mobilisation achievable through use of a variety of rod and screw arthrodises will optimise the chances of a full return to independent living in this

The goal with all of the surgical techniques used to treat rheumatoid cervical disease is to restore or preserve neurologic function. The precise technique used by the surgeon to achieve this will depend both on the individual radiological findings and on surgeon

In cases of atlantoaxial subluxation, without evidence of cranial settling, we advocate stabilisation of the C1-C2 segment through the use of transarticular screws (Krauss et al 2010). Careful scrutiny of preoperative CT imaging will identify cases where such screw trajectories are dangerous or impossible, such as abnormal positioning of the transverse

remains awake.

**9. Pre-operative traction** 

vulnerable patient cohort.

**10. C1C2 Transarticular screws** 

preference.

caloric intake, reducing risks of pneumonia or catabolism.

foraminae or aberrant vertebral artery (Ebraheim et al 1998, Golanki & Crockard 1999, Nagaria et al 2009). We routinely use stealth neuronavigation when planning screw trajectories to minimise the risk to both vertebral arteries and neural structures. In our experience myelopathic patients who have successful reduction and immobilisation of the C1C2 segment will not require laminar decompression. In cases of aberrant vertebral arteries we place a unilateral transarticular screw, with a lateral mass screw in C1 and a pars screw in C2 being placed on the "aberrant" side, if safe to do so, however, an aberrant vertebral artery can also preclude safe C2 pars screw insertion and we have not experienced any failures over a 15 year period with unilateral screw placement. Though some authors routinely reinforce their constructs with a Gallie or Brooks fusion, this has not been our practice. Successful placement of bilateral transarticular screws provides 38mm of fixation which more than adequately stabilises the segment (Yoshida et al 2006), without the added 5 - 7% risk of neurologic injury associated with wire constructs (Ebraheim et al 2000).

Having applied the Mayfield skull clamp either to the skull or to the halo ring itself if previously applied, an image intensifier is used to confirm correct alignment of the atlantoaxial joint and the subaxial cervical spine. A midline posterior incision from C1 arch to C2/C3 spinous interspace level is followed by a subperiosteal exposure of both atlas and axis, and of the occiput itself in cases of occipitocervical fusion. The posterior arches of C1 and C2 are exposed at C1 as far laterally as the medial border of the lateral mass and inferiorly as far as the C2/3 joint avoiding disruption of the joint itself. The destruction wrought by the rheumatoid inflammatory process on the normal anatomical landmarks of the atlas and axis makes placing C1-C2 screws without the use of neuronavigation hazardous at best, and foolhardy in some cases. The pars of C2 is exposed subperiostially as far as the C1/C2 joint remaining anterior to the traversing C2 root. Blunt dissection along the superior aspect of the C2 lamina allows the operator to appreciate the medial aspect of the C2 pedicle. Successful identification of the C2 pedicle and the pars as it extends superiorly toward the C1-C2 articulation, allows a safe entry into the C1-C2 joint. It is important in this area to maintain a subperiosteal approach with a sharp dissector to avoid venous haemorrhage. The joint may be entered, curetted and graft inserted directly. This step may be facilitated with the use of an operating microscope. It has been our practice to perform this additional step where the space between the articular surfaces of C1 and C2 allow it, particularly in those cases with incomplete reduction of C1 on C2. The approximate entry point for transarticular screw placement is 2mm lateral to the medial border of the C2-C3 facet joint. Stab incisions as per image guidance bilaterally allow the desired screw trajectory aiming toward the upper half of the C1 anterior tubercle. Use of neuronavigation to confirm screw trajectory minimises the danger of encountering either the vertebral artery (which may easily be damaged with a lateral or inferior trajectory (Geremia et al 1985) or the spinal cord. The vertebral artery is most at risk from a trajectory that is too low rather than one that is too lateral. This is especially important in cases when incomplete reduction of C1 and C2 has been achieved where an anterior target above the tubercle of C1 should be chosen. In these cases the choice of the anterior tubercle of C1 as a target causes a low trajectory through C2 with the risk of cortical perforation inferiorly. If this is kept in mind, incomplete reduction of C1 on C2 does not preclude C1/C2 transarticular screw fixation. An image-guided drill-guide is passed percutaneously to the posterior arch of C2, and aligned with the planned entry point on the neuronavigation. A guide K-wire is drilled

Surgical Considerations of Rheumatoid Disease

Fig. 5. Neuronavigation trajectory planning of a C1 screw

Involving the Craniocervical Junction and Atlantoaxial Vertebrae 289

into C2 using the drill-guide, and using lateral fluoroscopy to identify the trajectory to C1 through the C1-C2 joint toward the anterior tubercle of C1. Self-taping screws are passed over the K-wire, which is then safely removed. In cases of incomplete reduction, lag screws (partially threaded screws) may be used to improve the reduction.

Fig. 4. Trajectory of transarticular screws aiming toward the upper anterior.

Given that up to one-fifth of patients will not be suitable for bilateral safe placement of C1/C2 transarticular screws due to abnormal vertebral artery position (Wright & Lauryssen 1998), all available technologies to reduce the risk of potentially catastrophic vascular injury must be made available to the operating surgeon. The first clinical series involving the use of image guidance in C1/C2 transarticular screws demonstrated no neurovascular injuries in a series of 84 screws (38 bilateral and 8 unilateral) performed in 46 patients with atlantoaxial instability due to rheumatoid arthritis (Paramore et al 1996). Preoperative planning using the contiguous axial images allowed careful planning of the screw trajectory; keeping in mind the position of the intraosseous portion of the vertebral arteries, the diameter of the pars interarticularis and the quality of bone in the axis.

Independent review of postoperative radiographs by consultant radiologists confirmed good screw position in all instances. In 8 cases pre-operative assessment demonstrated a pars diameter which precluded the safe placement of a C2 pars screw, so alternative posterior stabilisation methods were undertaken on the reduced pars diameter side. Such is the biomechanical strength of a properly placed transarticular screw, however, that both in our own practice and those of other authors excellent results have been achieved with a unilateral transarticular screw and Philadelphia collar (Wigfield & Bolger 2001).

into C2 using the drill-guide, and using lateral fluoroscopy to identify the trajectory to C1 through the C1-C2 joint toward the anterior tubercle of C1. Self-taping screws are passed over the K-wire, which is then safely removed. In cases of incomplete reduction, lag

screws (partially threaded screws) may be used to improve the reduction.

Fig. 4. Trajectory of transarticular screws aiming toward the upper anterior.

pars interarticularis and the quality of bone in the axis.

Given that up to one-fifth of patients will not be suitable for bilateral safe placement of C1/C2 transarticular screws due to abnormal vertebral artery position (Wright & Lauryssen 1998), all available technologies to reduce the risk of potentially catastrophic vascular injury must be made available to the operating surgeon. The first clinical series involving the use of image guidance in C1/C2 transarticular screws demonstrated no neurovascular injuries in a series of 84 screws (38 bilateral and 8 unilateral) performed in 46 patients with atlantoaxial instability due to rheumatoid arthritis (Paramore et al 1996). Preoperative planning using the contiguous axial images allowed careful planning of the screw trajectory; keeping in mind the position of the intraosseous portion of the vertebral arteries, the diameter of the

Independent review of postoperative radiographs by consultant radiologists confirmed good screw position in all instances. In 8 cases pre-operative assessment demonstrated a pars diameter which precluded the safe placement of a C2 pars screw, so alternative posterior stabilisation methods were undertaken on the reduced pars diameter side. Such is the biomechanical strength of a properly placed transarticular screw, however, that both in our own practice and those of other authors excellent results have been achieved with a

unilateral transarticular screw and Philadelphia collar (Wigfield & Bolger 2001).

Fig. 5. Neuronavigation trajectory planning of a C1 screw

Surgical Considerations of Rheumatoid Disease

degree of surgical screw-placement freedom.

Involving the Craniocervical Junction and Atlantoaxial Vertebrae 291

Surgeons now have a choice of 2 types of occipital fusion systems. The older "Grob-style" plating system utilises the thick keel-like midline portion of the occipital bone, with the inverted Y-shaped plate being fixed to the occipital midline through a set of predetermined screw positions. The greater thickness of the bone in this location increases the pull-out resistance. We favour such plating systems where the occipital bone is intact. Our practice, however, involves treating patients who have commonly undergone previous suboccipital decompression, with loss of this midline portion of occipital bone. In such cases we more commonly utilise an "all-in-one" cervical rods with integrated occipital plates which are secured to the previously placed lateral mass/transarticular screws with locking cap screws. This construct allows the use of bicortical polyaxial screws of differing length, and also allows the surgeon to vary the screw position and trajectory. This 2-plate occipital fixation provides more rotational stability than the mid-line only Grob-plate occipital fixation. A variation on this solution is the use of modular plate rod constructs allowing a further

No clear biomechanical data exists regarding where the caudal-most screw fixation point ought to be placed. Our practice is to have at least 3 solid lateral mass screws or a transarticular screw and 2 lateral mass screw fixation points on each side of the subaxial spine to. The published literature does not give any guidance on which patients may be treated with constructs that end at the axis, and which patients require subaxial stabilisation as part of an occipitocervical fusion. Martin et al's (2010a) cadaveric study suggested that occipital plate and transarticular screw constructs restricted motion equally well whether or

Fig. 7. Occipitocervical fusion utilising transarticular screw fixation of the axis
