Treatment of atlantoaxial instability can be challenging in the pediatric patient. There are a number of treatment options including: posterior wiring; C1–2 transarticular screws; and Goel–Harms type fusion constructs. Each type of fusion has a unique set of risks and benefits and the choice of technique is related to the anatomy of the patient and their disease process and to the familiarity of the surgeon with any particular technique.
Wiring and cable techniques have a long history of effectively treating problems in the upper cervical spine. However, they are believed to be biomechanically less stable compared to transarticular screw and Goel–Harms constructs [11
]. Also, unlike wiring techniques, C1–2 transarticular screws and Goel–Harms constructs do not require that the patient be placed in a halo vest post-operatively. Additionally, C1–2 transarticular screws and Goel–Harms constructs provide stabilization and promotes fusion at just one intervertebral level, the diseased level, and minimize the degree to which it limits the range of motion of a patient.
C1–2 transarticular screws have been shown to be very effective at providing a solid fusion construct in pediatric patients with atlantoaxial instability [1
]. While transarticular screws can be safe and effective choice, their placement is technically demanding and in some patients, there are some potential advantages to the use of a Goel–Harms construct. First, the vertebral arteries have to have a particular anatomy to allow safe placement of C1–2 transarticular screws. If the artery has an unusual course, as has been shown to occur in 10–20% of adult patients, then a screw can not safely be placed on that side [26
]. In one study on pediatric patients, the authors found that the anatomy of the vertebral artery prevented safe placement of a transarticular screw in 11% of joint spaces [6
]. The Goel–Harms construct is thought to be less-dependant on the anatomy of the vertebral artery due to greater flexibility in screw trajectory. However, even with Goel–Harms constructs there remains a risk to the vertebral artery.
Brooks or Gallie type fusions require the passage of sub-laminar wires in the cervical spine. Likewise, after placement of transarticular screws, most surgeons augment the construct with a posterior fusion construct that involves passing sub-laminar wires and placement of an autograft taken form the iliac crest. The passage of sub-laminar wires in the cervical spine carries a 7–17% risk of neurologic deterioration, although these risks are felt to be lower at the atlantoaxial level [10
]. Also, if the posterior arch of C1 needs to be removed surgically for decompression or if it is incomplete as occurs in 1.5–5% of the population [15
], it would be difficult or impossible to place sub-laminar wires. Hypoplasia of the posterior arch of C1 is seen more often in some of the patients commonly treated for atlantoaxial instability [12
]. For example, it was seen in 28% of patients with Down syndrome [33
]. Because of the need for a C1 arch that will support posterior wiring, patients with congenital absence or a surgical removed C1 arch would not be candidates for transarticular screws or posterior wiring techniques but could be effectively treated with a Goel–Harms construct.
In most studies on C1–2 fusion autograft was taken from the hip or rib [1
]. Goel–Harms constructs do not require a structural graft so hip graft may not be needed. In the six patients presented here no hip autograft or rib was harvested. Instead we describe the use of local bone supplemented with sub-occipital bone if need. Not using hip graft may reduced the overall morbidity of the procedure by avoiding the 10–40% morbidity associated with iliac crest bone harvest [3
The proper placement of C1–2 transarticular screws requires that any subluxation at C1–2 be reduced prior to passage of the screw and the sub-laminar wires. Some patients cannot be reduced, and therefore could not undergo safe placement of C1–2 transarticular screws or passage of sub-laminar wires. A Goel–Harms construct allows intraoperative reduction of C1 on C2 after the placement of the screws [23
There are disadvantages to the use of C1 lateral mass screws and C2 pedicle screws or trans-laminar screws. Because more instrumentation is used compared to transarticular screws, these construct do have a greater cost. Also, compared to transarticular screws, Goel–Harms constructs do have an increased profile. However, in the patients presented here and in the large number of fusion constructs containing C1 lateral mass screws and C2 screws placed by the senior author, we have not had a case of wound dehiscence or breakdown, even in patients that were treated with radiation.