Shilla Growing Rods with Greater than 5 Years of Follow-up: Curve and Implant Characteristics John T. Wilkinson m.d., Chad E. Songy m.d., Frances l. mccullough, Richard E. mccarthy m.d. University of Arkansas for Medical sciences, little rock, ar

Background The Shilla procedure was designed for children with early onset spinal deformity as a means to correct spinal curvature while still harnessing a child’s remaining spinal growth. It allows for controlled axial skeletal growth within the construct and avoids the need for frequent surgeries to lengthen implants as with other distraction-based growing constructs. During surgical implantation of the Shilla, only the apex of the primary curve is instrumented with pedicle screws. The apex is then linked into spinal rods, corrected with derotation and coronal re-alignment, and fused. Additional levels above and below the apex are instrumented under fluoroscopic guidance within the subfascial layer and connected into the spinal rods with Shilla screws that permit movement along the rod as the spine continues to grow. A two-year follow up was previously published that showed improvement of coronal alignment from a preoperative average Cobb angle of 70.5 degrees to a postoperative average of 34 degrees. Also, the same study demonstrated a 13% increase in space available for the lungs and a 12% increase in truncal height.

Hypothesis Curve characteristics will evolve over time after initial apex fusion and placement of the Shilla implants. Rod fractures are an expected outcome in growing, active children.

Materials and Methods A retrospective review of all patients treated with the Shilla procedure by the senior surgeon was conducted to identify patients with Shilla implants in place for 5 years or greater. This review produced a total of 80 patients that have undergone this surgery, of which 21 had Shilla implants in place for 5 years or greater. Charts and radiographs were reviewed to compare coronal curve characteristics preoperatively, postoperatively, and at last follow up noting changes in the apex of the primary curve. Also noted was the development of adjacent compensatory curves, the overall vertical spinal growth, the incidence of rod fracture and screw pullout, and the need for definitive spinal fusion versus removal of the implant alone in patients that had reached skeletal maturity.

Results Of the 21 patients with greater than 5 years of follow up, 9 were male and 12 were female. All patients had significant early onset scoliosis warranting surgical treatment. Underlying diagnoses causing the spinal curvature included Syndromic (n=8), Neuromuscular (n=7), Idiopathic (n=5), and Congenital (n=1). The average age at index Shilla procedure was 6 years + 8 months (range 1yr + 11 mo to 11yrs + 10 mo). All 21 patients had the Shilla implants in place for a minimum of 60 months (5 years). The average length of time the implants were in place was 83.95 months (Range 60-128 months). The apex of the primary curve moved 2 vertebral levels or greater in 13/21 patients (61.9%) an average of 2.73 +/- 0.88 vertebral levels (range 2-5 levels).

Preoperative radiograph demonstrating a large left-sided thoracolumbar spinal curvature with a Cobb angle of 104 degrees and an apex at T12. B. First up-right post operative radiograph following correction and fusion of the apical segments using the Shilla growth guidance technique. C. Final spinal radiograph prior to removal of implants and definitive posterior spinal fusion demonstrating a distal migration of the apex of the left sided curvature below the previously fused apical levels. New apical level of the primary curve is centered at L3.

Results (cont) Of these, the apex shifted distally in 12 patients and proximally in 1 patient. 2 patients developed new, compensatory curves. Of the 21 patients included in this study, 14 have reached skeletal maturity and are “graduates” of the Shilla procedure. 11 graduates underwent definitive posterior spinal fusion and 3 patients maintained satisfactory spinal alignment throughout growth with the Shilla system and underwent implant removal alone. All patients demonstrated vertical spinal growth determined by T1-S1 length with the average growth being 45.5 mm (Range 6mm - 109mm). In evaluating implant failure, 6/21 patients experienced 1 episode of spinal rod fracture and 3/21 patients experienced 2 episodes of spinal rod fracture. 3/21 patients developed pullout of a pedicle screw.

Preoperative PA radiograph (inversion) demonstrating a 68 degree right thoracic spinal curvature without apparent involvement of the lower lumbar segments. B. First upright post-operative PA radiograph with improved coronal alignment of the primary thoracic curvature. C. Final PA radiograph prior to removal of the Shilla implants and definitive posterior spinal fusion 8 years and 8 months following index surgery demonstrating the development of a new 69 degree left sided thoracolumbar curve.

Summary This study constitutes the longest reported follow up of patients with early onset scoliosis treated with the Shilla procedure. We evaluated the change over time in curve characteristics and implant failures after the Shilla implants have been in place for at least five years. Our goal was to assess how the Shilla implants and the spinal curvature respond and change over the course of treatment as the child’s spine continues to grow. Results of this review suggest that the apex of the fused primary curve shifts in approximately 62% of patients with the majority of these involving a distal transition. All patients demonstrated continued spinal growth with an average increase in T1-S1 length of 45.5 mm of longitudinal growth. During the course of treatment, 11 patients had implant failures: 8 patients experienced rod fracture, 2 patients screw pull out and 1 patient experienced both. A better understanding of the long term follow up of Shilla patients will add to our fund of knowledge regarding this innovative growing spinal system.