Some Connectors in Distraction-based Growing Rods Fail More Than Others

Retrospective review of a prospectively collected patient cohort.

This study examined the rate of failure of various types of spinal rod connectors in distraction-based growing rod constructs for early-onset scoliosis.

Distraction-based growing rods have a high rate of reported complications.

We performed a retrospective review of a single surgeon's consecutive cases with growing rod constructs for early-onset scoliosis. Connector failure was defined as loosening of the connector-rod interface, which resulted in shortening of the construct and loss of distractive force. We included 30 patients with average age of 5 years (range, 1-10 years) with diagnoses of congenital scoliosis (15), neuromuscular (10), idiopathic (4), and other (1). Minimum follow-up was 2 years, with a mean follow-up of 49 months (range, 24-83 months).

Of 98 connectors, there were 12 connector failures (12.2%) in 9 patients. In all failures, the set screw loosened, resulting in rod slippage. On average, failures occurred 25.5 months after the index procedure, and after the third lengthening. Simple side-to-side closed connectors with circular slots had the highest rate of slippage (7 of 17; 41%). Side-to-side connectors with V-groove slots that mechanically lock the rod had 10 times fewer failures, (1 of 27; 4%) (p = .006). Only 1 of 34 longitudinal connectors failed (3%) (p = .002). The average T1-S1 gain during growth was 6.5 mm/year for patients with a connector failure and 9.0 mm/year for those who did not (p = .25). Connectors failed in dual rods (6 of 18; 33%) and single rods (6 of 15; 40%) at similar rates (p = .97).

Connector failure in distraction-based growing rods is associated with 28% less T1-S1 gain. Side-to-side connectors with circular slots had a failure rate of 41% compared with side-to-side connectors with V-groove slots (4%). Longitudinal connectors had a failure rate of 4%.