The Classification for Early-onset Scoliosis (C-EOS) Correlates With the Speed of Vertical Expandable Prosthetic Titanium Rib (VEPTR) Proximal Anchor Failure

Abstract

Background: The Classification for Early-onset Scoliosis (C-EOS) was developed by a consortium of early-onset scoliosis (EOS) surgeons. This study aims to examine if the C-EOS classification correlates with the speed (failure/unit time) of proximal anchor failure in EOS surgery patients.

Methods: A total of 106 EOS patients were retrospectively queried from an EOS database. All patients were treated with vertical expandable prosthetic titanium rib and experienced proximal anchor failure. Patients were classified by the C-EOS, which includes a term for etiology [C: Congenital (54.2%), M: Neuromuscular (32.3%), S: Syndromic (8.3%), I: Idiopathic (5.2%)], major curve angle [1: ≤20 degrees (0%), 2: 21 to 50 degrees (15.6%), 3: 51 to 90 degrees (66.7%), 4: >90 degrees (17.7%)], and kyphosis ["-": ≤20 (13.5%), "N": 21 to 50 (42.7%), "+": >50 (43.8%)]. Outcome was measured by time and number of lengthenings to failure.

Results: Analyzing C-EOS classes with >3 subjects, survival analysis demonstrates that the C-EOS discriminates low, medium, and high speed of failure. The low speed of failure group consisted of congenital/51-90/hypokyphosis (C3-) class. The medium-speed group consisted of congenital/51-90/normal and hyperkyphosis (C3N, C3+), and neuromuscular/51-90/hyperkyphosis (M3+) classes. The high-speed group consisted of neuromuscular/51-90/normal kyphosis (M3N), and neuromuscular/>90/normal and hyperkyphosis (M4N, M4+) classes. Significant differences were found in time (P<0.05) and number of expansions (P<0.05) before failure between congenital and neuromuscular classes.As isolated variables, neuromuscular etiology experienced a significantly faster time to failure compared with patients with idiopathic (P<0.001) and congenital (P=0.026) etiology. Patients with a major curve angle >90 degrees demonstrated significantly faster speed of failure compared with patients with major curve angle 21 to 50 degrees (P=0.011).

Conclusions: The ability of the C-EOS to discriminate the speeds of failure of the various classification subgroups supports its validity and demonstrates its potential use in guiding decision making. Further experience with the C-EOS may allow more tailored treatment, and perhaps better outcomes of patients with EOS.

Level of evidence: Level III.

FIGURE 1

The Classification for Early-onset Scoliosis (C-EOS). Etiology: (1) congenital/structural: curves developing due to a structural abnormality/asymmetry of the spine and/or thoracic cavity; includes hemivertebrae, fused ribs, postthoracotomy, or congenital diaphragmatic hernia; (2) neuromuscular: patients with neuromuscular disease (ie, spinal muscular atrophy, cerebral palsy, muscular dystrophies, etc.); (3) syndromic: syndromes with known or possible association with scoliosis (including spinal dysraphism). Idiopathic: no clear causal agent (can include children with a significant comorbidity that has no defined association with scoliosis). Major curve angle: measurement of major spinal curve in position of most gravity; maximum measurable kyphosis: between any 2 levels; annual progression ratio modifier (optional): progression per year; minimum = 6 months between observation: $$[(\text{Cobb}\text{at}{t}_2)-(\text{Cobb}\text{at}{t}_1)]\times \frac{12\text{months}}{[t_2-t_1]}.$$

FIGURE 2

Time to vertical expandable prosthetic titanium rib proximal fixation failure.

FIGURE 3

Mean time to failure by diagnosis. Neuromuscular versus idiopathic (P = 0.026). Neuromuscular versus congential (P < 0.001).

FIGURE 4

Mean time to failure by preoperative major curve angle. >90 degrees versus 21 to 50 degrees (P = 0.011). >90 degrees versus 51 to 90 degrees (P = 0.031).