Technical Advances in Pediatric Craniovertebral Junction Surgery Mark E. Oppenlander, James Kalyvas, Volker K.H. Sonntag, and Nicholas Theodore

Contents Introduction .............................................................................................................................. Posterior Approaches ............................................................................................................... Posterior Fixation Techniques............................................................................................ Considerations in the Very Young...................................................................................... Anterior Approaches ................................................................................................................ Transoral Decompression .................................................................................................. Odontoid Screw Fixation ................................................................................................... Image Guidance ....................................................................................................................... Monitoring ............................................................................................................................... Additional New Technologies .................................................................................................. Conclusions .............................................................................................................................. References ................................................................................................................................

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Abstract Surgery for conditions in the craniovertebral junction in the pediatric population poses unique challenges. The posterior approach has emerged as the gold standard for arthrodesis in this region. Anterior fixation or decompression also may be indicated. Intraoperative image guidance and neurophysiological monitoring improve the safety and efficacy of these procedures. The specific technical advances in surgery of the craniovertebral junction that have improved patient outcomes are reviewed. Keywords Craniovertebral junction surgery • Pediatrics • Arthrodesis • Image guidance • Neurophysiological monitoring

M.E. Oppenlander, MD • J. Kalyvas, MD • V.K.H. Sonntag, MD • N. Theodore, MD (*) Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, 350 W Thomas Rd, Phoenix, AZ 85013, USA e-mail: [email protected] C. Di Rocco, N. Akalan (eds.), Pediatric Craniovertebral Junction Diseases, Advances and Technical Standards in Neurosurgery 40, DOI 10.1007/978-3-319-01065-6_6, © Springer International Publishing Switzerland 2014

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Introduction Conditions involving the craniovertebral junction in children include congenital disorders, inflammatory conditions, traumatic dislocation or fracture, and neoplastic etiologies. Unique challenges are associated with surgery for decompression and internal fixation of the pediatric craniovertebral junction, including the small osseous structures and variable anatomy of children. These issues complicate both the diagnosis and treatment of craniovertebral disorders in this age group. Anterior and posterior approaches to the craniovertebral junction have been described in detail, reflecting a significant evolution in the surgical management of conditions affecting this region. Furthermore, techniques for intraoperative image guidance and neurophysiological monitoring continue to emerge for surgery of the craniovertebral junction. With these advances have come improvements in patient outcomes and rates of arthrodesis. This chapter outlines specific technical advances underlying this evolution.

Posterior Approaches Posterior Fixation Techniques The challenge of stabilizing the craniovertebral junction lies in the complex biomechanics and anatomy of the region. In the pediatric population, these issues are complicated by a skeletally immature spine and smaller bony landmarks. The posterior approach remains the standard for definitive arthrodesis of the craniovertebral junction, and several technical advances in instrumentation and techniques have led to a high rate of success in these patients [1, 2]. Early attempts to stabilize the craniovertebral junction utilized simple bone graft onlay techniques. Suboccipital and sublaminar wiring was introduced to secure the bone graft, but these methods still necessitated postoperative external rigid orthosis (Fig. 1) [21].Wiring techniques also often incorporated subaxial nonpathologic segments into the construct to ensure stability, thus necessitating increased surgical exposure while subsequently limiting the patient’s range of motion. Rod-and-wire fixation techniques, for example with the Steinmann pin, offer several advantages to earlier constructs. When used in combination with bone graft, this construct is associated with a higher rate of fusion [3, 15]. The use of a rod construct offers more rigid internal fixation, thus decreasing reliance on external orthosis. In the pediatric population, rod-and-wire may be an appropriate technique if anatomy limits the use of screws (Fig. 2) [21]. The rod-and-wire technique involves bending a rod into a U-shape and using sublaminar wires or braided cables to fixate the rod and bone graft to the occiput and cervical spine. As with graft-and-wire techniques, however, rod-and-wire may require incorporation of subaxial segments, further limiting range of motion.

Technical Advances in Pediatric Craniovertebral Junction Surgery Fig. 1 Graft-and-wire technique. A rib graft is wired to the occiput and the cervical laminae for occipitocervical fusion (Used with permission from Barrow Neurological Institute)

Fig. 2 Rod-and-wire technique. Occipitocervical fixation and fusion are accomplished by securing a threaded Steinmann pin to the craniovertebral junction with wire or braided cable (Used with permission from Barrow Neurological Institute)

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Fig. 3 Atlantoaxial fixation, combining the DickmanSonntag interspinous fusion technique with transarticular screws (Used with permission from Barrow Neurological Institute)

Biomechanically, both graft-and-wire as well as rod-and-wire techniques are inferior to rigid screw-based techniques [6]. Specific attention has focused on the interspinous methods of fixating the atlas to the axis. These methods place a bone graft between the spinous processes of C1 and C2. A braided cable then places the graft under compression, providing a posterior buttress to promote bony fusion. Specific examples include the Brooks fusion [5] or the Dickman-Sonntag technique [7]. As with other grafting techniques, the interspinous graft is made more biomechanically rigid when combined with screw fixation (Fig. 3). The introduction of screw-based techniques for craniovertebral junction fixation offers superior biomechanical rigidity compared with previous constructs [7]. Furthermore, screw fixation is feasible in the pediatric population as long as the patient has no precluding anatomic constraints [21]. Early screw-based constructs utilized lateral mass plates, whereas new constructs use polyaxial screw heads and rods (Fig. 4). The rods may be composed of a variety of metals, most commonly stainless steel, titanium, or Vitallium (cobalt chromium). Titanium is lighter weight and produces lower artifact on imaging when compared with stainless steel, whereas Vitallium has similar stiffness to stainless steel while still retaining the light weight and low imaging artifact of titanium [13]. Numerous options for screw fixation of the atlantoaxial complex have been described. Transarticular screw fixation, described by Magerl and Seeman [16], results in a stable and rigid construct (Fig. 3). Combining C1 lateral mass screws with C2 pars or C2 pedicle screws offers similar biomechanics to the transarticular construct [17]. C2 translaminar screws are an alternative if unsuitable anatomy excludes pars articularis or pedicle screws at the C2 level [27]. The choice of any particular screw option depends on the patient’s anatomy and surgeon’s preference. The transarticular screw, for example, is infeasible in as many as 23 % of cases because of unfavorable anatomy [18]. New screw-based techniques for the occiput have also evolved. Earlier constructs utilized bilateral plates or rods extending from the bilateral occipital regions.

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Fig. 4 Occipitocervical fusion with screw-based constructs. (a) Early screw-plate system. (b) Modern construct using polyaxial screw heads and rods (Used with permission from Barrow Neurological Institute)

This method has the disadvantage of fixating to a point lateral to midline on the occiput where the bone is thinner. Newer constructs fixate the occiput in the midline keel where bone is thickest and screw purchase is maximized. Combining screwbased rigid fixation with bone graft support maximizes stability and the likelihood of bony fusion (Fig. 5).

Considerations in the Very Young Craniovertebral junction pathology and fixation techniques in the very young pediatric population (

Technical advances in pediatric craniovertebral junction surgery.

Surgery for conditions in the craniovertebral junction in the pediatric population poses unique challenges. The posterior approach has emerged as the ...
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