LIV selection in 'tweener' patients treated with magnetically controlled growing rods vs. posterior spinal fusion.

Purpose: The purpose of this study was to compare the LIV selection in 'tweener' patients treated with MCGR or PSF.

Methods: A multicenter pediatric spine database was queried for ambulatory patients ages 8-11 years treated by MCGR or PSF with at least 2-year follow-up. The relationship between the LIV and preoperative spinal height, curve magnitude, and implant type were assessed. The relationship between the touched vertebrae (TV), the last substantially touched vertebrae (LSTV), the stable vertebrae (SV), and the LIV were evaluated.

Results: One hundred and fifty-nine patients met inclusion criteria. Preoperative curve magnitude was similar between groups (MCGR 68 ± 19.0° vs. PSF 66 ± 17.2°, p = 0.6). Preoperative curve magnitude was associated with LIV, as larger curves were associated with a more caudal LIV (p = 0.0004). Distribution of the LIV was more varied in PSF compared to MCGR. L3 was the LIV in 43% of MCGR patients compared to 27% of PSF patients. A thoracic LIV was more common in the PSF group (PSF 13% vs. MCGR 1.2%, p = 0.0038). The LIV was cephalad to the SV in 68% of PSF compared to 48% of MCGR patients (p = 0.02).

Conclusion: The majority of LIV selection in 'tweener' patients was at L3 or below regardless of surgical strategy, likely driven by curve magnitude. However, 'tweener' patients treated with PSF had more cephalad LIV selections compared to patients treated with MCGR. Potential LIV differences should be considered when selecting MCGR vs. PSF in 'tweener' patients.

Level of evidence: III.