13 Surgical Options: The Shilla Procedure

The various etiologic diagnoses in early onset scoliosis all lead to a common pathway—namely, that of thoracic insufficiency syndrome. The diagnoses generally are classified as having idiopathic, syndromic, neuromuscular, or congenital causes. The long-term outcome of untreated early onset scoliosis is severe compromise of respiratory function, evidenced by pulmonary function study values that are less than 20% of predicted values; furthermore, respiratory compromise is correlated with early death according to the studies of Pehrsson et al, ¹ who compared death rates in patients with infantile scoliosis with expected death rates in unaffected adults. Death due to respiratory compromise in children who have early onset scoliosis has been observed even in those younger than 10 years of age.

The previously accepted dictum of treatment with early fusion to produce a straight spine has resulted, in many cases, with short thoracic height, compromised pulmonary function, and early death. ^{2 ,​ 3 ,​ 4} The fallacy of this treatment method has been shown by many and has encouraged the development of expandable prostheses that promote an increase in thoracic height and an expansion of pulmonary capacity. However, what are the costs of this approach? Distraction techniques, commonly used in many centers, not only require repeated trips to the operating room for lengthening but also foster the development of proximal junctional kyphosis. This can be a source of an unsightly kyphotic deformity, with prominence of the spinal implants and potential skin breakdown over the implants. There is also a loss of growth centers around the anchor points, whether they are screws or hooks, where localized fusion is used to stabilize the anchor points and create platforms to be pushed apart through distraction.

Ankylosis and autofusion of the facet joints has been noted in patients followed to maturity as a consequence of the partial immobilization caused by the rods and results in the law of diminishing return with subsequent lengthening procedures and, in essence, a loss of potential growth. ^{5 ,​ 6} Chest wall stiffness results from vertical expandable prosthetic titanium rib (VEPTR) treatment, and its ultimate effect on respiratory function is unknown. There is also evidence that repeated trips to the operating room cause cognitive delays and adversely affect early childhood development. ⁷ Skin problems, with an increased risk for infection and scarring, are commonplace in patients who undergo repeated lengthening procedures.

These issues raise questions as we plan the future treatment of early onset scoliosis. For instance, why not direct the corrective forces toward the most curved section of the spine, the apex? And why not place the anchor points where there is maximal deformity? If one is going to use the apex as the anchor point, why not correct the deformity in all planes, fixing rotation as well as coronal and sagittal misalignment? Furthermore, the normal growth rate of a child’s spine is the rate at which the spine grows normally; growth does not occur as a sudden burst of distraction every 6 months with artificial lengthening.

Part of the answer to this dilemma has been addressed through a treatment modality known as growth guidance, which is analogous to directing the growth of a young tree. A stake is placed alongside the spine that allows the spine to proceed with its normal rate of growth, and the stake is held to an anchor that encourages straightening. Eduardo Luque used this technique in the 1970s and 1980s in what was characterized as the Luque trolley, in which wires were lashed to the posterior elements of the spine and around a smooth rod, allowing gradual elongation through growth. The problem with the anchor points was that dissection of the periosteum to place the wires resulted in premature fusion and inconsistent elongation, so that this technique fell into disfavor in most surgeons’ hands.

A newer modification of the idea was developed in which pedicle screws were used as anchors, but the technique was inspired by the techniques for the manipulation and correction of spinal deformities demonstrated by Se Suk of Seoul, Korea. ⁸ The Shilla was born of a desire to harness spinal growth and guide correction more naturally. The apex of the curvature is corrected in all planes—coronal, sagittal, and axial—and is fused and firmly anchored to the rod while growing screws are placed through the muscle levels above and below the apex. The periosteum is not disrupted for growing screw placement, allowing normal patterns of growth and minimizing return trips to the operating room. This concept was tested in the laboratory in goats; studies showed that at the 6-month interval, all of the animals manifested growth across the expanse of their instrumentation and at both the upper and lower aspects of the construct. ⁹ The surgical technique is unique in that there is subperiosteal exposure only at the three or four levels at the apex of the curvature; the levels are identified with the use of small needles on the spinous processes and the C-arm. The apex is treated with Ponte osteotomies, bilateral pedicle screws at each level, and a derotation maneuver. ¹⁰ The fascia is released superiorly and inferiorly from this point 1 cm off the midline, allowing introduction of the Shilla growing screws through the muscle layer under fluoroscopic guidance. The cannulated screws are best placed with Jamshidi needles. Cannulated screws can be placed in a freehand manner as well. Either the screws have a cap that fits to the top of the polyaxial portion or a closed head screw can be used, allowing the rod to slide through the center of the screw head. The rod is therefore captured but not bound by the screw head. The growing screws are placed at intervals above and below the apex and are sufficient to control the alignment and keep the curve as neutral as possible in the coronal and sagittal planes.

During the last 8 years, the Shilla technique has been used for many diagnoses, including idiopathic scoliosis, spina bifida, cerebral palsy, and multiple different syndromes, as well as for certain congenital curves. The data regarding these patients was first presented to the Scoliosis Research Society in 2008, when a cohort of 48 patients from two centers was reported; at that time, only 10 patients had had 2 years of follow-up. The average curve treated was 70 degrees, and the results reflected curve correction that was maintained over time, an increase in the space available for lung, and an increase in truncal height, both immediately after surgery and over time with further growth. In 2009, the number of procedures was analyzed, and among 22 patients with more than 2 years of follow-up, an additional 26 procedures after the initial index procedure had been recorded. It was calculated that if these patients had undergone lengthening procedures on a 6-month basis, an additional 115 surgical procedures would have been necessary, along with any unplanned procedures. In a report on a cohort of 40 patients in 2011, it was emphasized that any return to the operating room constituted a complication and that this group of patients, with 52 additional trips to the operating room, had been spared the anticipated 250 procedures they would have undergone if treated with a surgical distraction technique.

Several things were learned from this surgical experience. One of these was a recognition of the need for the preoperative release of stiff curves, or at least a period of preoperative traction, to acquire the mobility necessary for correction to be achieved at one sitting. It was also noted that direct vertebral derotation was an important part of the surgical treatment. For stiffer curves, it was found that a temporary rod on the convexity is helpful to gain provisional correction, and with the use of coronal benders, the apex can be pushed toward a concave rod, the permanent rod required to maintain correction, and subsequently a permanent rod is placed along the convexity.

A child’s level of activity can also affect the longevity of an implant. In more active children, the components tend to loosen, so that screws back out of the pedicles. Although this was not a problem from a neurologic standpoint, some of the implants did become prominent, and a decision had to be made either to tolerate this effect or change the screw site on an outpatient basis. These were some of the reasons for additional surgeries.

Pelvic obliquity is seen primarily in patients with neuromuscular scoliosis. Flexible pelvic obliquity is best treated by carrying the growing screws low into the lumbar spine, to either L4 or L5. For more rigid pelvic obliquity, an anterior release may be necessary to gain flexibility. In that instance, a stronger construct is necessary to maintain correction, and iliac wing screws combined with S1 or S2 screws should provide sufficiently firm fixation to allow a fixed rod to be joined to a growing screw in the lower lumbar spine, attached to a cross connector or domino box, fixed to one rod with Allen setscrews, and allowed to slide along the rod on the opposite side. With the use of domino connectors on both the right and left sides, the pelvic obliquity can be controlled reasonably well and growth over time allowed.

One of the questions every practitioner of growth rod treatment raises is, What is the best thing to do for the patient at maturity? The experience that we have had with Shilla rods is similar to that seen with distraction rod systems. The question at maturity is whether the rods should be left in place, replaced with permanent rods and fusion, or removed entirely. The most common option is removal of the growing rods and insertion of a permanent fused system that achieves a final correction at the time of the fusion. This technique is exemplified by the patient in Fig. 13.1 , in whom a growing rod had been inserted during a period of active growth. After 2 years of activity, the rod had broken and sufficient maturity had been achieved to allow a permanent fusion and definitive correction of the residual deformity. Another option may be simply to remove the metallic device and allow the spine to maintain the alignment previously achieved through the growth guidance technique.

In summary, the Shilla procedure harnesses a child’s inherent growth potential while avoiding the problems of premature fusion and ankylosis associated with the Luque trolley system. However, the placement of pedicle screws in small patients requires caution and can be challenging. The Shilla procedure does not require repeated trips to the operating room and allows a more normal childhood, free of bracing, casts, and repeated trips to the operating room, in which the patient is able to participate in most childhood activities, including many sports.

Related posts:

15 Complications of Growing Rod Treatment 14 The Experts’ View: A Narrative of the Great Debate 15 Complications of Growing Rod Treatment 12 Dual Growing Rod Treatment 2 Development of the Spine 22 Nonoperative Treatment of Syndromic Scoliosis

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