Spinal growth : deciphering the rosetta stone

Abstract

Skeletal maturity indices are important measures for determining the growth potential remaining of patients with idiopathic scoliosis. Inaccurate growth assessment can be held responsible for any curve deterioration post-treatment. It can be due to the insensitivity of skeletal maturity index, or growth parameters being unable to represent growth accurately. Little is known about the interactions between different skeletal maturity indices, and how their characteristics can be better utilized together to aid in clinical decision making. The objectives of this study are to investigate whether skeletal maturity indices can be used in combination to effectively indicate pubertal growth landmarks, how that conjunctive use can be applied in clinical practice, and whether a new skeletal maturity index can be established for idiopathic scoliosis with spinal growth and cervical vertebral growth, without the need of additional hand-wrist radiographs.

Patients diagnosed with idiopathic scoliosis attending the tertiary scoliosis clinic between 2014 and 2018 were studied. The simplified olecranon method, Risser staging, Sanders staging and distal radius and ulna (DRU) classification were investigated for their extent of coverage of different phases of pubertal growth period and their use in combination. Further analyses focused on the clinical context, including how peak growth related to peak curve progression, the role of baseline skeletal maturity in final height prediction, and how ulnar grading refined Sanders stage (SS) 7 for brace-wear weaning. Patients were prospectively recruited with whole spine radiographs, from which the proximal femur epiphyseal ossification was used for establishing the Proximal Femur Maturity Index (PFMI). C3-C7, T1-T12, T1-S1 and L1-L5 spine length and the sagittal mid-vertebral body height of C3, C4, C5, C6, C7 were assessed as growth parameters.

For immature patients, DRU and simplified olecranon method can be used for the growth acceleration phase, whereas Sanders staging and DRU classification were found having adequate coverage of the deceleration growth phase until skeletal maturity, with all three indices to be used in combination for peak growth. R6, U5, SS3 and Risser stage 0 + were effective in indicating peak growth, and SS6/7 with U7/8 were relatively most effective in indicating the beginning of growth plateau. The use of SS7 combined with ulnar grade 7/8 resulted in no curve progression immediate post-brace weaning for curve < 40°. There was lagging identified for the timing of peak curve progression versus peak growth by one DRU grade. The newly established PFMI demonstrated satisfactory reliability and reproducibility, and was capable in capturing the acceleration-deceleration pubertal growth patterns using standing/sitting body height, spine length and vertebral height especially at C5. Peak growth occurred at femur grade 3.

The use of multiple skeletal maturity indices strategically in combination can provide comprehensive coverage of the entire pubertal growth period. The convenient viewing of proximal femur on whole spine radiographs not only help avoiding radiation exposure, the growth at the vertebral column in terms of spinal and cervical vertebral growth coupled with PFMI can provide useful skeletal maturity measure in idiopathic scoliosis. The impact of curve progression on growth is yet to be determined.