T1-T12 and T1-S1 Lengths at Maturity in Patients With Skeletal Dysplasia

Background: Growing-spine surgery aims to promote thoracic growth in skeletally immature patients by achieving adequate T1-T12 length. Surgical decision-making often relies on assumptions regarding spinal length thresholds and their relationships to cardiopulmonary function. This study aimed to characterize thoracic (T1-T12) and total spine (T1-S1) lengths in skeletally mature patients with skeletal dysplasias, with a primary focus on achondroplasia, and to evaluate whether these measurements were associated with cardiopulmonary comorbidities. Methods: A retrospective review was conducted of skeletally mature patients with confirmed skeletal dysplasia evaluated at a single institution between 2018 and 2023. Patients with scoliosis >30 degrees or prior spinal deformity surgery were excluded. T1-T12 and T1-S1 lengths were measured using the Pediatric Spine Study Group (PSSG) methodology. Patients with achondroplasia were analyzed as the primary cohort, with patients with short-trunk skeletal dysplasia, including spondyloepiphyseal dysplasia (SED) and mucopolysaccharidosis type IV (MPS IV), serving as a contextual comparison group. Results: Of 68 patients aged (mean and SD) 37±16.7 y, 58 had achondroplasia and 10 had other skeletal dysplasias. In the cohort, mean T1-T12 and T1-S1 lengths were 26.2 and 43.3 cm, respectively. Patients with achondroplasia demonstrated greater T1-T12 (27.8±2.8 cm vs. 21.1±5.0 cm; P <0.001) and T1-S1 (46.1±4.4 cm vs. 35.6±7.1 cm; P <0.001) spinal lengths than short-trunk skeletal dysplasia patients. Cardiopulmonary comorbidities were present in 6 patients (9%) and were not clearly associated with spinal length. Conclusions: Skeletally mature patients with skeletal dysplasias, particularly achondroplasia, can achieve T1-T12 and T1-S1 lengths within expected adult ranges. These findings provide reference data for spinal length at maturity in patients with achondroplasia, with contextual comparison to related short-trunk skeletal dysplasias, and may help inform expectations regarding thoracic growth and cardiopulmonary risk in the context of growth-friendly surgical treatment. Level of Evidence: Level IV.