special considerations for surgical fusion of the occiput and … · 2017. 11. 30. · general...

Special Considerations for Surgical Fusionof the Occiput and Cervical Spine

Kyle G. Halvorson and Douglas L. Brockmeyer

ContentsGeneral Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Anatomy and Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Surgical Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Occipitocervical Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Normal Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Congenital Vertebral Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Post-Chiari Decompression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7General Concepts in Surgical Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Craniocervical Fusions in the Very Young Patient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Atlantoaxial Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Surgical Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Patient Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14C1-2 Transarticular Screw Constructs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Goel-Harms Construct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Bone Grafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Complication Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Postoperative Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Long-Term Alignment and Cervical Spine Growth After Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

K.G. HalvorsonDepartment of Neurosurgery, Division of Pediatric Neurosurgery, University of Utah, PrimaryChildren’s Medical Center, Salt Lake City, UT, USA

D.L. Brockmeyer (*)Department of Neurosurgery, Division of Pediatric Neurosurgery, University of Utah, PrimaryChildren’s Medical Center, Salt Lake City, UT, USA

Department of Neurosurgery, Clinical Neurosciences Center, University of Utah,Salt Lake City, UT, USAe-mail: [email protected]; [email protected]

# Springer International Publishing AG 2018C. Di Rocco et al. (eds.), Textbook of Pediatric Neurosurgery,https://doi.org/10.1007/978-3-319-31512-6_128-1

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mailto:[email protected]

mailto:[email protected]

https://doi.org/10.1007/978-3-319-31512-6_128-1

General Introduction

Craniocervical fixation in children presents a variety of unique and challengingconcerns for the pediatric spine surgeon. Some of these concerns include smalland/or abnormal anatomy, the need for accommodation of growth and development,and the availability of appropriately sized instrumentation. Despite these challenges,modern instrumentation and biological agents (such as graft extenders and rhBMP(recombinant human bone morphogenetic protein)) can accommodate a suitablesurgical option in almost every case. Thus, a successful occipitocervical (OC) fusionis possible in the vast majority of children.

Children with OC instability can present with a variety of signs and symptoms.A careful history and physical examination are critical when investigating thepresenting complaints. Sometimes children with congenital instability are asymp-tomatic, yet others may present with some degree of neck pain, torticollis, weakness,numbness, tingling, bowel or bladder incontinence, or vascular insufficiency. How-ever, there are scenarios, such as atlantooccipital dislocation (AOD), where themechanism of injury and radiographic findings will be the primary factors determin-ing surgical decision making.

Not all craniocervical imaging abnormalities and instability issues require imme-diate intervention. For example, some children with Down syndrome may toleratea significant amount of OC or atlantoaxial motion before surgical intervention isrequired or may not require intervention at all (Brockmeyer 1999). In selected cases,conservative management is indicated, provided there is no evidence of neurologicaldeficit or progressive deformity. Very young patients (under the age of 2 years) withOC instability can often be temporized with an external brace until definitive surgicalstabilization can be performed.

The goals of this chapter are to: (1) provide information on the appropriateselection of patients for surgical intervention and (2) discuss special considerationsinto the techniques and management of those cases that require fusion. On thesecond topic, these considerations will be broken down into three patient groups:(1) those with normal anatomy; (2) those with congenital vertebral anomalies; and(3) those with post-Chiari decompression instability.

Anatomy and Indications

Anatomy

The craniovertebral junction (CVJ) develops from several distinct embryologicstructures, eventually forming the axis, atlas, occipital bone, clivus, occipital con-dyles, and ligaments. The main articulation of the skull with the cervical spine occursat the atlantooccipital joints, which are primarily stabilized by the atlantooccipitalcapsular ligaments and transverse ligament. The tectorial membrane, alar ligaments,and apical ligaments are minor stabilizing structures at the OC junction. The primarymotion at occiput-C1 is flexion and extension, contributing to approximately 50% ofthe flexion-extension motion of the entire cervical spine.

2 K.G. Halvorson and D.L. Brockmeyer

C1 lacks a true vertebral body. Instead, it consists of a ring with medial/posteriorprojecting inferior facets articulating with the axis and superior facets articulatingwith the occipital condyle. The C1-2 joint relies primarily on the transverse ligamentand atlantoaxial capsular ligaments for its stability (Panjabi et al. 1978). The C1-2joint is designed to facilitate rotation, with the C1 ring acting as a washer. There is nodisk at the C1-2 level, and the lateral mass articulations are flat in orientation. Forfurther information regarding the anatomy and embryology of the cervical spine,please refer to the appropriate references (Brockmeyer 2006).

Surgical Indications

There are several causes of OC instability that require surgical fusion in pediatricpatients: trauma, congenital conditions, infection, neoplasms, and iatrogenic treat-ments (such as post-Chiari decompression). Each condition has a different presen-tation, but the underlying theme is that for each patient the OC joint is unstableenough that conservative treatment is not likely to succeed. The above diagnosesdeserve a few brief comments, discussed below.

First, traumatic OC instability in the pediatric population is quite common andis known as AOD. For many years, ratios and indirect measurements of theoccipitoatlantal joint were used to determine if OC instability was present. However,in a series of landmark papers, Pang et al. (2007a, b) described the condylar-C1interval, or CCI, as the distance found on a CT scan between the occipital condyleand superior articular surface of C1. Their work strongly suggested that the CCImethod of assessing instability was better than previous methods and implicated theoccipitoatlantal ligaments as important determinants of stability. Since then, furtherwork has found that any CCI measuring �2.5 mm on a sagittal plane and 3.5 mm ona coronal plane signifies potential instability (Ravindra et al. 2017). For traumaticC1-2 instability, Panjabi et al. (1978) suggested an atlantodental interval (ADI)>5 mm would constitute abnormal motion; however, they also found ADIs of upto 6 mm in cadavers of normal children younger than 10 years old. For practicalpurposes, isolated traumatic C1-2 instability is relatively rare in the pediatric agegroup and often occurs as a combination injury with AOD. It is diagnosed usinga combination of magnetic resonance imaging (MRI), computed tomography (CT),and plain x-rays, including flexion and extension views.

Second, congenital OC instability is relatively common. The most commonsyndromic cause of OC instability is Down syndrome, where both OC and C1-2instability may be seen. In Down syndrome, the occipitoatlantal joint often has a flatconfiguration instead of the typical cup shape. As a result, a high degree ofoccipitoatlantal instability may exist because of this flattened joint (Browd et al.2006, 2008). In patients with Down syndrome, occipitoatlantal translation >10 mm,ADI >6–8 mm, or a neural canal width <12 mm are potential indications forsurgical fusion.

Other congenital causes of OC instability include bony dysplasia. Anatomicalvariations in the craniocervical bony morphology may include dysplastic C2 pars,dysplastic occipital condyles, and C1 hemirings, to name a few. C1 hemirings can

Special Considerations for Surgical Fusion of the Occiput and Cervical. . . 3

be highly unstable in the infant and toddler population (Brockmeyer et al. 2011). Osodontoideum, or even an anaplastic/hypoplastic dens, can also cause congenitalinstability. Severe symptomatic basilar invagination that is irreducible outside theoperating room is also a potential indication for ventral decompression and posteriorfusion (Menezes 2012).

Tumors and infectious causes of OC instability are less common but can occur inthe setting of osteomyelitis, Langerhans cell histiocytosis, and sarcomas, amongothers.

Iatrogenic OC instability may occur when either bony or ligamentous supportstructures have been surgically removed, as in the case of Chiari decompression orafter resection of a large craniocervical tumor such as a chordoma. For Chiari-relatedinstability, excessive bone removal or progressive craniocervical kyphosis is oftenthe cause of the problem. Recent work has identified both Chiari 1.5 malformationand a craniocervical angle of less than 125� as risk factors for fusion (Bollo et al.2012).

Occipitocervical Fusion

There are three general populations of children that require craniocervical fusion.The first group consists of those with normal anatomy. The second group includeschildren with congenital vertebral anomalies, while the third group consists ofchildren who have previously undergone suboccipital decompression for Chiari1 malformation.

Normal Anatomy

For children in the first group, craniocervical fixation is relatively straightforward.Typically, it involves creating solid screw fixation at C2 and the occiput, witha connecting rod or plate system in between (Medtronic, Vertex Select, Minneapolis,MN) (Fig. 1). These patients primarily have AOD or Down syndrome (Figs. 2and 3). Options for C2 fixation include pars, translaminar, transarticular, or pediclescrews. Options for occipital fixation include the midline keel, the occipital condyle,or inside-outside hardware systems (K2M, Caspian Occipital Anchor Spinal System,Leesburg, VA).

Potential difficulties in this group can be seen in very young patients (under2 years of age) and those with bone anatomy that creates a difficult C2 screwpurchase. A high-riding vertebral artery at C2 can create insufficient space foradequate C2 screw purchase. Likewise, very thin bone in the suboccipital regioncan result in insufficient screw purchase. Strategies for dealing with these issues havebeen published (Brockmeyer et al. 2000) and typically involve finding other safescrew trajectories using C2 translaminar screws or perhaps even condylar screws(Bekelis et al. 2010; Uribe et al. 2008). As a general rule, the surgeon must not befocused on a particular screw pathway, as significant anatomic variation exists among


patients. One must instead look for the best screw trajectory in each patient and foreach side to provide the best purchase and highest pull-out strength. As a last resort,sublaminar wiring can provide fixation but care and ingenuity must be exercised toachieve an adequate result.

The fusion substrate is from either an autologous or an allogenic source. Autol-ogous options include rib, iliac crest, or split thickness occipital bone. Allogenicsources include iliac crest or morcellized bone chips. Adjuncts to enhance fusioninclude rhBMP-2 (Infuse Bone Graft, Medtronic) or demineralized bone matrix.Intra-articular fusion is also an option and is preferred in many centers. Thistechnique consists of drilling into the joint space and then packing it with eitherallograft or local autograft.

Congenital Vertebral Anomalies

The second group of patients to discuss includes those with congenital vertebralanomalies. Successful fusion procedures in these patients always require significantpreoperative planning and sometimes considerable surgical skill and ingenuity. Forinstance, in children with congenital vertebral anomalies of the CVJ, such as C1hemirings or axis anomalies, there can be significant anatomical limitations thatcreate difficulty in finding a site for adequate screw purchase (Fig. 4) (Brockmeyeret al. 2011). Children with Klippel-Feil syndrome can have occipitalization of theaxis, coupled with unique bony segmentation anomalies of the subaxial spine,making the identification of normal landmarks difficult. In children with

Fig. 1 Normal anatomy.Demonstration of an occiput-to-C2 fusion construct. C2pars screws with rib allograftand rod plate/cable constructin a child with normalanatomy are depicted(Reproduced with permission.# Department ofNeurosurgery, University ofUtah)


neurofibromatosis type 1, profound cervical kyphosis due to ligamentous or bonyabnormalities may develop, with scalloping of the vertebral bodies as a hallmark.Common skeletal dysplasias, such as mucopolysaccharidosis IV (Morquio syn-drome), spondyloepiphyseal dysplasia, osteogenesis imperfecta, and diastrophicdwarfism, can also present significant challenges (Fig. 5). These patients may havelower bone quality and short stature, making screw placement less adequate. Other,rarer, syndromes include Goldenhar, Conradi, Grisel, Larsen, and Hurler syndromes.These children have challenges that are similar in nature to those discussed above.

Strategies for fixation may require using different screw trajectory pathways oneither side of the patient’s vertebral bodies, or even unilateral constructs (Fig. 6)(Mazur et al. 2015). Additionally, multiple backup plans, even including haloplacement, should be ready for implementation should one of the more ideal screwlocations fail. Screw placement also demands that the surgeon is well versed in the

Fig. 2 This 3-year-old boy was involved in a high-speed motor vehicle accident. He was restrainedin a forward-facing car seat. He was admitted with a dense quadriparesis that slowly improved over1 month. (a) Parasagittal short tau inversion recovery MRI of the cervical spine showing abnormalsignal intensity within the occiput C1 and C1-2 joints (arrows). (b) Midsagittal T2-weightedcervical MRI showing extensive injury to the posterior ligamentous structures and abnormal signalintensity anterior and superior to the odontoid, both indicative to atlanto-occipital dislocation.(c) Parasagittal cervical CT scan showing distraction at the atlantooccipital joint with a CCI of5.5 mm. The C1-2 joint is also slightly distracted and angulated forward (asterisk). (d) ParasagittalCT scan showing severe disruption of the atlantooccipital joint with a CCI of 7 mm. (e) Postoper-ative cervical spine film demonstrating intact hardware at the occipital cervical joint with bilateralC2 pars screws and occipital screw construct. The posterior rib graft can be seen and is held in placeby a multi-stranded titanium cable (Reproduced with permission. © Department of Neurosurgery,University of Utah)


techniques involved in C2 pars, C2 translaminar, C2 pedicle, and C1-2 transarticularscrew placement. In children with NF1 and severe kyphosis, anterior cervicaldiskectomies, corpectomies, and fusion constructs may be necessary prior toperforming these posterior techniques. Routine use of intraoperative fluoroscopy,and, if available, intraoperative CT scanning with the O-arm (Medtronic Corp.,Minneapolis, MN) are extremely helpful for visualization and confirmation of instru-mentation placement while still in the operating room.

Post-Chiari Decompression

The third group of children to consider involves those with Chiari-related indicationsfor craniocervical fusion (Fig. 7). These patients have frequently undergoneprevious suboccipital craniectomy and C1 laminectomy. They often have abnormalcraniocervical anatomy such as craniocervical kyphosis, retroflexed odontoid, bas-ilar invagination, and axis assimilation. The fact that a suboccipital craniectomyhas already been performed reduces the amount of bone available for screw purchaseand bone apposition. The decision to proceed with OC fusion can be very

Fig. 3 This is a 7-year-old female patient with Down syndrome and OC instability. (a, b) Lateralcervical spine flexion/extension films showing severe occipitoatlantal subluxation measuring14 mm taken together. (c, d) Parasagittal cervical spine CT scans demonstrating flat occipitalatlantoaxial joints, typical for Down syndrome. (e) Postoperative lateral cervical spine filmsshowing intact OC instrumentation with bilateral C2 pars screws and occipital screws. The ribgraft can be seen and is held in place by a multistranded titanium cable (arrow) (Reproduced withpermission. © Department of Neurosurgery, University of Utah)


challenging and is typically based both on the patient’s symptoms and their imaging.A helpful guideline to consider in the surgical decision-making process is that if thecraniocervical angle is <125� and a Chiari 1.5 malformation is present, thenthe chance of a craniocervical fusion preventing further reoperation is high (Bolloet al. 2012) (Fig. 8).

Once the decision to proceed with surgery is made, the surgeon must decide ifthere is evidence of persistent tonsillar herniation or syringomyelia. Then the priorChiari decompression site is explored and additional tonsillopexy and duraplastyare performed. The surgeon then proceeds to the instrumentation and fusion portionof the procedure, usually with placement of bilateral C2 pars screws, which areconnected to the occiput via a rod-plate system. Other instrumentation options, suchas condylar screws, have been used as well with good success. If intraoperativeodontoid reduction is required, the surgeon may break scrub to manually performthe reduction, with the assistant locking the hardware in place once reduction isachieved. The reduction is confirmed with intraoperative fluoroscopy andreconfirmed with an O-arm spin at the end of the procedure. Typically, rib autograftsare harvested because they are the only source of autograft that can be harvested in

Fig. 4. A 6-year-old girl presented with spondyloepiphyseal dysplasia and OC instability. (a, b)Lateral cervical spine flexion/extension films showing severe atlantooccipital instability and mildoccipitoatlantal instability. (c) Coronal two-dimensional CT reconstruction showing absence ofodontoid (arrow) and lateral displacement of the C1 lateral masses (asterisks). (d) Lateral cervicalspine CT scan demonstrating hypoplastic odontoid and severe vertebral dysplasia. (e) Parasagittalpostoperative CT scan showing mature occipital cervical arthrodesis from occiput to C2. (f)Postoperative lateral cervical spine film demonstrating intact hardware from occiput to C2. Oneside contains a pars screw (asterisk) and the other side has a translaminar screw (arrow)(Reproduced with permission. © Department of Neurosurgery, University of Utah)


sufficient length. The rib grafts are secured into place with a multistranded titaniumcable at the cervical end and maxillofacial screws at the occipital end. Small pledgetsof rhBMP are placed under the proximal and distal ends of the rib autograft wherethe rib contacts the occiput or cervical vertebral bodies (Kim et al. 2004).

General Concepts in Surgical Planning

Committing a child to a craniocervical fusion is a significant decision. An extensivereview of the available imaging, including plain cervical spine films with flexion andextension views, CT scans, and MRI scans, is critical. If concern exists over thelocation or course of the vertebral artery, a CT angiogram or conventional digitalsubtraction angiogram may be necessary. This is especially important in cases ofatlantoaxial instability where C1-2 transarticular screws are being considered forfixation. When reviewing imaging of the vertebral artery, the location of the groovein the superior aspect of the C2 lamina is assessed. Up to 25% of children may havea high-riding vertebral artery, making transarticular screw placement unfeasible(Menezes 2012; Brockmeyer et al. 2000). In the rare case where a child is beingconsidered for a halo orthosis, a head CT to assess for pin site location and bonequality can also be helpful to avoid complications related to placement (Menezes2012). Reformatted head CT with bone windows can also be helpful for review ofthe anatomy of the midline keel and to identify the optimum location for occipitalscrew placement. Review of only one modality is often insufficient to fully

Fig. 5 Congenital vertebralanomalies. Demonstration ofan occiput-to-C2 fusionconstruct in a child withcongenital C1 hemi-ringanomaly. Note the laterallydisplaced C1 lateral masses aswell as the abnormal C1-C2joints bilaterally. In thesecases, unilateral rod plate withrib allograft and C2 laminarscrew constructs may be allthat is technically feasible, butthis will still allow for solidfusion (Reproduced withpermission. # Department ofNeurosurgery, University ofUtah)


appreciate the complexity of the anatomy, as well as the possible surgical pitfalls.Key points to consider while reviewing these studies include:

1. Proper identification of the unstable levels. A precise diagnosis of the patient’sdisease and knowledge of the relevant anatomy drives this part of the surgicaldecision-making.

2. Identification of the appropriate levels requiring instrumentation. Fusing levelsthat do not need to be fused is a common mistake in pediatric craniocervicalsurgery. Typically, for a craniocervical fusion, instrumenting from occiput to C2is enough. Including C1 lateral mass screws into the construct does not lead tobetter outcomes (Hankinson et al. 2010). Likewise, including levels below C2into the construct is rarely, if ever, required, unless a congenital fusion at thoselevels is already present.

Fig. 6 Steps demonstrating placement of OC hardware in a patient with congenital instability andC1 hemi-rings. (a) Placement of C2 pars screw on the right and C2 translaminar screw on the left.(b) Placement of OC instrumentation from the occiput to C2 using rod–plate instrumentation.(c) Placement of bilateral rib autografts with screw placement through the top of the rib into theocciput. (d) Placement of a multistranded titanium cable around the instrumentation to push the ribgraft against the lamina of C2 (Reproduced with permission. # Department of Neurosurgery,University of Utah)


3. Identify safe corridors for instrumentation placement. This information isobtained by careful review of the appropriate radiographs. If new to thesetechniques, the surgeon should be conservative in his judgement in this regard.

4. In certain circumstances, a unilateral construct may be required. In a highlyunstable patient with unfavorable anatomy, if the choice is between good screwpurchase with a unilateral construct versus fair to poor screw purchase witha bilateral construct, the unilateral construct is most likely the better choice.

5. Identify the specific type of instrumentation that will provide the best result. Thisincludes the use of top-loading rod/plate systems, occipital plate systems, andinside-out systems. They all have their advantages and disadvantages, and thesurgeon should remember that one solution is not always best for every patient.

6. Choose the appropriate bone grafting material. This includes the use of allograft,local autograft, or harvested autograft and takes into consideration all of thepotential donor site morbidity if autograft is chosen.

7. Decide whether demineralized bone matrix or rhBMP might improve the chanceof a successful result. There is not a lot of high-quality evidence that supportstheir use in pediatric craniocervical fusion, but many surgeons use them routinely.

8. Sometimes preoperative traction for reduction of an alignment abnormality isnecessary. Typically, most pediatric craniocervical deformities are fairly flexibleand reducible in the operating room, but for those that are not flexible, preoper-ative traction can be very helpful.

9. Intraoperative neuromonitoring (IONM) is an important adjunct. It is mandatoryto use IONM if there is neural compression or intraoperative reduction isnecessary.

Fig. 7 Post-Chiaridecompression.Demonstration ofmodification of an occiput-to-C2 fusion construct in a childthat has undergonesuboccipital decompressionfor a Chiari malformation.Note the absence of the C1lamina and midline occipitalkeel (Reproduced withpermission. # Department ofNeurosurgery, University ofUtah)


Fig. 8 A 12-year-old girl with a Chiari 1.5 malformation and retroflexed odontoid was treated witha suboccipital decompression and duraplasty for significant headache symptoms. (a) Preoperativemidsagittal MRI scan demonstrates a Chiari 1.5 malformation and retroflexed odontoid. The clival-axial angle (CXA) is 128� and pBC2 (maximum perpendicular distance to the basion-inferoposterior point of the C2 body) is 10 mm. (b) Midsagittal MRI scan 2 years after the previousimage. The CXA has decreased to 113� and the pBC2 has increased to 12 mm. (c) Intraoperativelateral cervical spine fluoroscopy demonstrating drill pathway for placement of C2 pars screw. (d)Placement of top-loading C2 instrumentation in the C2 pars. (e) Postoperative parasagittal CTreconstruction demonstrating satisfactory placement of C2 pedicle screw. (f) Parasagittal CTreconstruction demonstrating satisfactory fusion from occiput to C2 (Reproduced with permission.© Department of Neurosurgery, University of Utah)


Craniocervical Fusions in the Very Young Patient

Special consideration should be given to craniocervical fusion procedures in veryyoung patients, defined as 3 years of age or less. The most common circumstance toperform this procedure is in AOD, although occasionally children with severecongenital instability will require it as well. Careful preoperative analysis of thepatient’s films to assess the adequacy of the anatomy to receive instrumentation iscritical. Typically, only the C2 pars and midline occipital keel will provide enoughbone for adequate screw purchase, but occasionally C2 translaminar or pediclescrews can be used. Furthermore, because very young children often have a higherproportion of cartilaginous-type tissue making up their cervical spinal anatomy,precise screw placement is critical because few backup options exist (Crostelliet al. 2009).

As for the instrumentation, the smallest commercially available cervical screwhas a diameter of 3.5 mm, and the drill bit used to place the pilot hole is 2.7 mm. Asa result, the pilot holes are not tapped before placing the screws. Either a rod/plate oran occipital plate system is typically used to fixate the cervical vertebra to theocciput. Because of the technical challenge of such procedures, intraoperativedocumentation of screw placement using the O-arm is highly desirable.

Atlantoaxial Fusion

Surgical Planning

In order to place C1-2 instrumentation, it is mandatory to review multiplanar CTreconstructions of the patient’s anatomy. Reviewing the atlantoaxial anatomy inmultiple two-dimensional planes allows the surgeon to recognize and understanda safe and optimum trajectory. For transarticular screws, the surgeon begins with theparasagittal reconstructions, with screw entry points or “trajectory origins” selectedclose to the C2-3 joint on each side (Fig. 9, right side). These sites of origin havebeen described as “3 mm superior to the C2-3 facet joint line and 3 mm lateral to thelamina lateral mass junction” (Menezes 2012). Once the entry points are selected, anaxial reconstruction is reviewed to determine the medial-lateral angle of the screwtrajectory, typically 2–5� medial. Next, a slightly off-parasagittal axis reconstructionis re-reviewed to assure the screw remains within bone for its entire course. Forcompleteness and to assure the best possible trajectory, the “trajectory origin” can bemoved a small increment lateral or medial and the process above repeated. The mostideal trajectory is then selected. The screw should pass through the C2 parsinterarticularis, the C1-2 joint space, and the lateral mass of C1. The target locationfor the screw tip is at the anterior tubercle of C1 while visualized intraoperativelywith fluoroscopy.

The Goel-Harms construct (C1 lateral mass screws coupled to C2 pars screws) isalso a popular option for atlantoaxial fixation (Fig. 9, left side). A safe C2 pars screwtrajectory is common in children, but C1 lateral mass screws can be challenging to


place because of the presence of the venous vascular plexus in the area. Thereforesome surgeons routinely take the C2 nerve root during the C1 lateral mass dissection,which has been shown to be safe and effective in large case series (Goel et al. 2002).

In some cases, preoperative reduction with muscle relaxants and cervical tractionmay be required prior to proceeding to cervical fusion. Atlantoaxial rotation sec-ondary to infections of the head and neck (Grisel syndrome) or minor trauma mayresolve with reduction outside the operating room. In a small number of cases,C1-C2 fusion may be required because of transverse ligament incompetence(Brockmeyer 2006). Preoperative analysis and planning are necessary to understandwhether in-line reduction, translation, or rotation will be possible intraoperatively.

Patient Positioning

After intubation, the patient is placed in a Mayfield pin head holder while stillsupine. This is done even in patients as young as 2 years of age. IONM is used,with baseline, “pre-flip” responses obtained before final positioning. The patient isthen carefully flipped prone, and the head and neck are placed in a neutral position.In cases of atlantoaxial fusion, a moderate “military tuck” position, with the neckflexed and chin slightly tucked, is used to give a better trajectory for C1-2 trans-articular or C2 pars screws. In patients with osteogenesis imperfecta, a paddedhorseshoe head holder is employed instead pins because of the risk of skull fractureand potential brain injury. We do not routinely use reinforced endotracheal tubes. Allpressure points are padded with foam prior to securing the Mayfield holder to the

Fig. 9 Goel-Harms andC1-C2 transarticular screwconstructs. On the left, astandard Goel-Harms styleconstruct is depicted with C1lateral mass and C2 parsinstrumentation. On the right,a C1-C2 transarticularconstruct is demonstrated(Reproduced with permission.# Department ofNeurosurgery, University ofUtah)


table. We then confirm our positioning with fluoroscopy prior to any further prep-ping and draping.

C1-2 Transarticular Screw Constructs

Fine-cut reformatted CT scans of the CVJ as well as the remainder of the cervicalspine are critical to identify the course of the vertebral artery as well as to assess anypresent congenital anomaly that may preclude screw placement. Before making theskin incision, it is critical that the surgeon is aware of the local anatomical landmarksthat will guide the selection of a starting point for screw trajectory. Routine review ofthe bony anatomy along the entire planned length of the screw is also essential (Glufand Brockmeyer 2005). In general, we use 3.5-mm-outer-diameter screws forpatients 4 years of age and younger and 4-mm-outer-diameter screws for patientsolder than the age of 4 years.

A paramedian incision is typically made bilaterally to obtain the steep trajectoryneeded to place the screw. A guide tube is passed through this incision via which firstan awl, then a drill, and then a tap are passed, and finally the screw is placed. Thistechnique also reduces disruption of the paraspinal musculature and reducesintraoperative blood loss. If an errant screw does injure the vertebral artery, thescrew is left in place for tamponade purposes and a postoperative angiographicevaluation carried out. Stereotactic guidance, while possible in adult patients, iscumbersome and less than ideal for pediatric patients given the size of the referencearrays relative to the patient’s anatomical size and working corridor. Therefore, thissurgical adjunct is not routinely used (Gluf and Brockmeyer 2005).

Goel-Harms Construct

The Goel-Harms construct was developed in the 1990s by Goel and popularized byHarms (Goel 2002, 2008a, b; Goel and Laheri 2002). This construct consists ofa screw placed into the C1 lateral mass with a polyaxial head and partially threadedshank. A C2 pars screw, also with polyaxial heads, is then placed and connected viaa top-loading rod to the C1 screws (Fig. 9, left side). An iliac crest autograft orallograft cable arrangement may supplement the hardware in some cases. As men-tioned above, placement of C1 lateral mass screws can be technically demanding inpediatric patients, and the Goel-Harms construct relies on strong, well-placed C2lateral mass screws for fusion. This construct is biomechanically similar to C1-2transarticular screws when done properly and may decrease the risk of vertebralartery injury (Menezes 2012).

Bone Grafts

The Sonntag-Dickman interspinous method, using a single interposition iliac crestgraft between the posterior tubercle of the C1 ring and the spinous process of C2, is


typically used. Interlaminar fixation with rib autograft has also had good success andmay be structurally and biologically better than iliac crest owing to a higher tensilestrength and increased concentrations of naturally produced BMP. Intralaminarfusion with rib autografting has been noted to have a fusion success rate of 98%(Menezes 2012; Dickman et al. 1991).

Complication Avoidance

Intraoperative complications may be avoided by practicing good preoperative plan-ning and precise surgical technique, using appropriate surgical adjuncts, andmaintaining awareness of patient-specific comorbidities (Hwang et al. 2012).Table 1 lists some common postoperative complications and associated mitigationstrategies based on a review by Menezes (2012). Avoiding surgical site infectionsrelies on good sterile technique during preparation of the surgical site, thoroughhemostasis, appropriately timed perioperative antibiotics, and the use of short-termpostoperative drains. Swallowing, breathing, or other discomfort related to the finalposition of the patient’s hardware can be avoided by careful analysis of intraoperativefluoroscopy (Hwang et al. 2012). Additionally, much can be gained from assessingthe patient’s head position after wound closure. Hyperflexion, extension, or lateralrotation can be observed simply by looking at the patient as he or she is positioned inthe Mayfield head holder. Adjacent segment disease can be reduced by appropriatesubperiosteal dissection with avoidance of subperiosteal hematomas, which cansubsequently calcify (Crostelli et al. 2009). Nonunion and pseudarthrosis are riskswith any fusion construct and necessitate revision of the fusion if they occur.Evidence of a “halo” around a screw on postoperative imaging indicates a loosescrew and instability. This will typically require hardware and fusion revision, withplacement of new screws using a different trajectory. The rare complication ofhypoglossal nerve injury or pharyngeal penetration with a C1 screw indicates thatthis screw is too long and must be retracted. Otolaryngological consultation iswarranted for pharyngeal repair should this occur (Menezes 2012).

Postoperative Management

After completion of an OC fusion in a child, follow-up with monthly cervicalradiographs at the 1-month, 2-month, and 3-month postoperative time points isnecessary to assure that adequate arthrodesis has been achieved. At the 4-monthmark, a cervical CT is obtained for detailed analysis of the status of the fusionprocess. Evidence of a bony bridge from the occiput to the lowest instrumentedvertebral level assures the fusion has taken. If there is a question of completion of thefusion but evidence suggests that the process is progressing, repeat CT scans beobtained at 2–3-month intervals. Yearly follow-up for those patients that haveachieved fusion is done by cervical lateral plain films. These are generally adequate


to assess spinal alignment and overall growth across the fusion segment and to ruleout proximal or distal junctional kyphosis or other adjacent-segment disease.

Long-Term Alignment and Cervical Spine Growth After Fusion

A multicenter 2006 study of long-term alignment and cervical spine growth afterfusion in 17 patients followed for a mean of 28 months demonstrated no sagittalmalalignment, subaxial instability, osteophyte formation, or unintended fusion ofadjacent levels (Anderson et al. 2006). The lordotic curve did increase from 15�

postoperatively to 27� across the follow-up period. An average of 34% of thecervical spine vertical growth occurred across the fusion segment. These findingswere confirmed in a recent study in 2016 by Kennedy et al. (2016), where mostyoung children undergoing atlantoaxial and OC fusion with rigid internal fixation

Table 1 Operative complications and mitigation strategies for craniocervical fusions in children

Complication type Mitigation strategies

Failure to extubate/prematureextubation

Prolonged prone positioning can lead to significantairway edema, and failure to extubate or prematureextubation can be devastating and therefore thissituation needs to be recognized. Close monitoring andcorticosteroids will generally resolve this issue over thecourse of a few days postoperatively

Loss of IONM or poor postoperativefunctional status

Pre-positioning baseline motor and sensory evokedpotentials can be helpful in patients where bony andligamentous alignment will change dramatically duringthe procedure. Reversal of the last maneuver after aloss, assuring good profusion pressure (mean arterialpressure), optimization of hematocrit and blood pH,normothermia, discussion with anesthesia regardingneuromuscular blockade and inhalation anesthetics,checking electrode position, and consideration of awake-up test can help revive lost monitoring signals

Excessive bleeding during C1 lateralmass exposure

Subperiosteal dissection of the C1 lateral mass, gooduse of hemostatic agents and packing, as well aspossible sacrifice of the C2 nerve root to coagulateepidural venous plexus vessels can assist withreduction in bleeding

Vertebral artery injury Place and leave screw for tamponade purposes. If theinjury occurs during placement of the first screw, do notproceed with placement of the screw on the oppositeside. Postoperative angiography is necessary

Cerebrospinal fluid leak or bleedingfrom occipital screw placement

Place and leave screw

Delayed neurologic decline Concern for epidural clot or seroma from BMP,potentially leave drain if BMP used, imaging to rule outhematoma, evacuate if present

Modified from Menezes (2012)


were found to have good cervical alignment and continued growth within the fusedlevels during a prolonged follow-up period. However, some variability in verticalgrowth and alignment existed, highlighting the need to continue close long-termfollow-up. Overall, the literature supports no significant limitation in growth poten-tial after fusion, nor any hastening of alignment problems.

Conclusion

OC fusion in pediatric patients is always a serious and challenging undertaking. Bytaking the structured, methodical approach outlined in this chapter, a pediatric spinesurgeon can ensure the best care for patients while improving his/her chances forsuccess.

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