Parasol Rib Deformity in Hypotonic Neuromuscular Scoliosis: A New Radiographical Definition and a Comparison of Short-term Treatment Outcomes With VEPTR and Growing Rods.

STUDY DESIGN: Retrospective review of 2 multicenter national databases, Growing Spine Study Group and Chest Wall and Spine Deformity.

OBJECTIVE: To derive an objective measure of parasol rib deformity from spine radiographs and to compare efficacy of rib-based (vertical expandable prosthetic titanium rib (VEPTR)) versus spine-based growing rods ("GR") instrumentation to improve parasol rib deformity and pulmonary function.

SUMMARY OF BACKGROUND DATA: Children with low tone neuromuscular scoliosis often develop collapse of the rib cage ("parasol rib deformity") that may be associated with poor pulmonary function.

METHODS: We compared patients with hypotonic neuromuscular scoliosis treated by VEPTR or GR with greater than 1 year follow-up. Preoperative and final spine radiographs were assessed for parasol rib collapse, spine asymmetry, and thoracic deformity. Multivariable analysis was performed on these measurements to identify the best descriptor of parasol rib deformity. Using this measurement, the ability of VEPTR versus GR to control parasol rib deformity was then compared. Assisted ventilation rating (AVR) at preoperative and final follow-up was compared between the 2 groups.

RESULTS: Twenty-three patients treated with VEPTR (average age 6.7 years, average f/u = 3.3 years) were compared with 22 patients treated with GR (average age 7.7 years, average f/u = 2.9 years). The equation Parasol Score = (T6 convex hemithoracic width/T6 concave hemithoracic width) × (T6 thoracic width/T12 thoracic width) was the most accurate descriptor rib collapse (AUC = 0.927). Parasol Score was correlated with AVR. Parasol Score did not change over time for the patients treated with GR, but had a tendency to worsen for patients treated with VEPTR. AVR did not change significantly in either group. Spine deformity was better corrected using GR.

CONCLUSION: Parasol rib deformity, measured on x-ray by the metric = (T6 width convex hemithorax/T6 width concave hemithorax)*(T6 thoracic width/T12 thoracic width), did not improve after treatment with VEPTR or GR. AVR did not change significantly in either group.

LEVEL OF EVIDENCE: 4.