The Spring Distraction System for Growth-Friendly Surgical Treatment of Early Onset Scoliosis: A Preliminary Report on Clinical Results and Safety after Design Iterations in a Prospective Clinical Trial

Abstract

Background: The Spring Distraction System (SDS) is a dynamic growth-friendly implant to treat early onset scoliosis (EOS). Previous SDS studies showed promising results in terms of curve correction and complication profile. Nevertheless, complications did occur, which led to modifications in the implant design. The main iterations were a larger rod diameter and a more sagittal stable sliding mechanism. The purpose of this study was to investigate the performance of these iterations. Methods: All patients treated with the modified SDS and >1 year follow-up were included. Radiographic outcomes, severe adverse events (SAEs), unplanned returns to the operating room (UPRORs) and health-related quality of life (HRQoL) were investigated. Results: Seventeen EOS patients (three congenital, four idiopathic, nine neuromuscular, one syndromic) were included. Mean age at surgery was 9.5 ± 2.5 years. Similar to the first generation SDS, about 50% initial correction was achieved and maintained, and spinal growth was near physiological. Most importantly, SAEs and UPRORs were diminished and favorable with 0.10/patient/year. In addition, HRQoL increased during the first year postoperatively, indicating the implant was well accepted. Conclusion: These preliminary results indicate that the iterations of the SDS are effective in terms of reducing SAEs and UPRORs and increasing HRQoL in patients with EOS.

Keywords: curve correction; dynamic; early onset scoliosis; growth; growth-friendly; patient-reported outcome measures; severe adverse events; spring distraction system; unplanned returns to the operating room; versatile.

Figure 1

The Spring Distraction System. (Left) First-generation SDS with three components added to the 4.5 mm rods: a side-to-side connector (green) with one oversized hole that was kept unlocked, a compressed spring (gold) that provides a 75 N distraction force and a locking buttress (blue). (Right) Current SDS with 5.5 mm rods and an extra parallel connector. Moreover, an increased portfolio of springs with a 50 N and a 100 N version.

Figure 2

Different SDS configurations: (1) A 10-year-old male with neuromuscular scoliosis with a bilateral system with concave and convex springs fixated to S1, note the fully distracted spring after two years. (2) A 10-year-old male with an idiopathic-like scoliosis treated with a hybrid system with a concave spring and a convex sliding rod fixated with an apical screw. (3) A 7-year-old female with a congenital scoliosis treated with a unilateral system with a concave spring and convex hemi-epiphysiodesis. (4) A 9-year-old female with syndromic scoliosis treated with a unilateral system with a concave spring only.

Figure 3

Coronal Cobb changes. (Left) Primary Cobb angle (°) changes over time. (Right) Secondary Cobb (°) angle over time.

Figure 4

Sagittal Profiles. (Left) T5–T12 kyphosis (°) over time. (Right) L1–S1 lordosis (°) over time.

Figure 5

Spinal height changes. (Left) T1–T12 height (mm) over time. (Right) T1–S1 height (mm) over time.

Figure 6

Overall mean scores of the Early-Onset Scoliosis Questionnaire plotted over time.