**11. Occipital-cervical fusion**

The occipitocervical junction (consisting of the occipitoatlantoaxial complex) is a multi-joint complex of 4 synovial joints. An important biomechanical nuance to be overcome when fusing this joint complex is the sharp angle between the occiput and the upper cervical spine readily appreciable on lateral x-rays or MRI sagittal views. This sharp angle makes access to the joints quite challenging in rheumatoid patients and also contributes, along with the 5kg weight of the head, to a large moment arm necessitating the most rigid of constructs. Unfortunately fusion and immobilisation of this junction will eliminate up to 50% of the normal range of motion of the head and neck. Our main indication for such "drastic" reduction in mobility in rheumatoid patients is in cases with a large ventral pannus causing cord compression.

The most common complications, other than infection and persistent neck pain, are fixation of the patient's head in an excessively flexed or extended position, thereby increasing the risk of falls in an already vulnerable and sometimes unsteady patient cohort. Our practice of placing these patients pre-operatively in a HALO-brace will accomplish the dual goals of checking whether the ventral compression is relieved on distraction (through visualisation of CSF anterior to the cord on MRI), and will allow the physiotherapists to check patient safety on mobilising.

Though historically the cervical fixation was achieved with interspinous wiring or lateral mass wiring in combination with preformed rods such as the Ransford loop, our practice is to use lateral mass or transarticular screws, with off-set connectors if necessary as the bony anatomy is commonly distorted in rheumatoid patients. These more modern techniques have demonstrated higher fusion rates (Shad et al 2002, Kelleher et al 2008) and lower pseudoarthrosis rates (Abumi et al 1999) when compared to their wire-based predecessors.

Fig. 6. Lateral radiograph demonstrating bilateral C1C2 transarticular screw placement

The occipitocervical junction (consisting of the occipitoatlantoaxial complex) is a multi-joint complex of 4 synovial joints. An important biomechanical nuance to be overcome when fusing this joint complex is the sharp angle between the occiput and the upper cervical spine readily appreciable on lateral x-rays or MRI sagittal views. This sharp angle makes access to the joints quite challenging in rheumatoid patients and also contributes, along with the 5kg weight of the head, to a large moment arm necessitating the most rigid of constructs. Unfortunately fusion and immobilisation of this junction will eliminate up to 50% of the normal range of motion of the head and neck. Our main indication for such "drastic" reduction in mobility in rheumatoid patients is in cases with a large ventral pannus causing

The most common complications, other than infection and persistent neck pain, are fixation of the patient's head in an excessively flexed or extended position, thereby increasing the risk of falls in an already vulnerable and sometimes unsteady patient cohort. Our practice of placing these patients pre-operatively in a HALO-brace will accomplish the dual goals of checking whether the ventral compression is relieved on distraction (through visualisation of CSF anterior to the cord on MRI), and will allow the physiotherapists to check patient

Though historically the cervical fixation was achieved with interspinous wiring or lateral mass wiring in combination with preformed rods such as the Ransford loop, our practice is to use lateral mass or transarticular screws, with off-set connectors if necessary as the bony anatomy is commonly distorted in rheumatoid patients. These more modern techniques have demonstrated higher fusion rates (Shad et al 2002, Kelleher et al 2008) and lower pseudoarthrosis rates (Abumi et al 1999) when compared to their wire-based predecessors.

**11. Occipital-cervical fusion** 

cord compression.

safety on mobilising.

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 degree of surgical screw-placement freedom.

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

Surgical Considerations of Rheumatoid Disease

rheumatoid cervical fusions (Heller et al 1991).

**12. C1 Lateral mass screw placement** 

the use of this technique (Gunnarsson et al 2007).

1984, Lee et al 2006).

**13. Anterior approaches** 

Involving the Craniocervical Junction and Atlantoaxial Vertebrae 293

schedule after such fusions to enhance healing rates. Despite poor bone quality we have not encountered any incidents of screw pull-out or construct-failure in our published series of

Though we prefer to use C1/C2 transarticular screws, anatomical or surgical circumstances pertaining to this challenging patient cohort occasionally mandate the use of C1 lateral mass screws. C1 lateral mass screws are technically demanding, but we do use them regularly in cases of rheumatoid C1-2 fusions. These may be inserted in cases in which transarticular screws are contraindicated because of anatomic constraints. Such cases include patients with anomalous vertebral arteries, though in such cases it is essential to show on 3D CT that placement of a C2 pars screw is possible. Seventeen (18%) of 94 patients had a high-riding transverse foramen on at least one side of the axis that would prohibit the placement of conventional C1/C2 transarticular screws (Mummaneni & Haid 2005, Nagaria et al 2009). C1 lateral mass screw-rod constructs are preferred over conventional atlantoaxial transarticular screws by certain authors due to a variety of factors (Paramore et al 1996, Currian & Yaszemski 2004). The C1 lateral mass screws can be inserted before reduction of the atlantoaxial joints, thereby enabling the surgeon to use the screws as method of achieving a reduction. The screws do not violate the C1-2 joints, and therefore they can be used for temporary immobilization in trauma patients; however this is not a consideration in the rheumatoid patient. C1 lateral mass screws can also be used when the C1 arch is deficient. The presence of an arcuate foramen (ponticulus posticus) in the atlas, seen in up to 18% of cases, through which the vertebral artery and first cervical nerve traverse, precludes

Beginning the passage of C1 lateral mass screw can be quite a challenge due to the almost constant presence of a venous plexus at the insertion site caudal to the posterior lateral arch of the atlas. We use a combination of Surgicel and thrombin glue to achieve haemostasis, and a slightly more rostral entry point, on the posterior lateral arch itself using a pneumatic drill to drill away the undersurface of the posterior lateral arch. Using such an entry point, in conjunction with neuronavigation, allows one to avoid the vertebral artery and spinal cord, whilst also avoiding the worst of the bleeding from the venous plexus. Such an approach is possible in over 85% of cases (Huang & Glaser 2003). The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1 lateral mass screws. Some authors have advocated use of unicortical C1 lateral mass screws in order to avoid such potential complications. Such opinions are supported by biomechanical data showing greater pull-out strength of both unicortical and bicortical C1 lateral mass screws compared with subaxial lateral mass screws. Our practice however is to aim for bicortical purchase, given the absence of adequate comparative data for rheumatoid patients, and the greater risk of screw pullout due to the tendency of the underlying rheumatoid disease to cause osteoporosis of the vertebrae (Wordsworth et al

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

not subaxial fixation were included as part of the construct. Criticisms such as the femaleonly nature of the cadaveric specimens and the use of non-contiguous subaxial fixation points have been robustly refuted by the authors as being of limited clinical relevance.

Nowhere in spine surgery is the concept of ultimate mechanical fatigue and subsequent failure of greater importance than at the occipitocervical junction. The large moment arm generated with an adult head and the steep angles required in excessively lordotic porotic rheumatoid cervical spine account for these high failure figures. We use a combination of the autologous bone-chippings on the decorticated bone surfaces, and osteoconductive and osteoinductive bone void-fillers superimposed on our construct to maximise the chance of securing bony fusion. Osseous fusion is necessary for ultimate success of this procedure, as in its absence metal fatigue and subsequent catastrophic construct failure is virtually guaranteed. Rigid internal fixation at time of surgery obviates the need for use of postoperative HALO-bracing, though a custom-fitted Miami-J collar beneath the patient's chin will prevent premature excessive neck flexion and screw pull-out. Careful adherence to a professionally devised and supervised nutrition programme is also part of any follow-up

Fig. 8. Occipitocervical fusion using a transarticular screw fixation of the C1C2 complex, and lateral mass fixation of C3-C7. The construct was extended into the upper thoracic levels. Note that single screws were only possible at the C3 and C4 levels

schedule after such fusions to enhance healing rates. Despite poor bone quality we have not encountered any incidents of screw pull-out or construct-failure in our published series of rheumatoid cervical fusions (Heller et al 1991).
