The thumb ossification composite index is the optimal intersection between Sanders and low-dose scoliosis sterioradiography.

PURPOSE: Skeletal maturity assessment may be performed using low-dose scoliosis radiographs (LDSS) with simultaneous imaging of the hand or proximal humerus. We sought to compare the practicality, reliability and validity of the Sanders skeletal maturity staging (SMSS), proximal humerus ossification system (PHOS) and the thumb ossification composite index (TOCI) as skeletal maturity assessment tools using LDSS.
METHODS: A survey including 85 LDSS and 42 hand radiographs was administered to four orthopedic clinicians. Each rater assessed the TOCI, SMSS and PHOS stage for each image. Standing LDSS with hands at the patient's side were used for TOCI, SMSS, and PHOS measurements. SMSS and TOCI measurements on dedicated hand radiographs were assessed as a comparison. Interobserver reliability was calculated for each scale using Fleiss' kappa. For SMSS and TOCI, intraobserver correlation between measurements on LDSS and measurements on hand radiographs were also assessed.
RESULTS: 472 TOCI measurements, 288 SMSS measurements, and 340 measurements were collected. Kappa interobserver reliability for TOCI was 0.79 (strong) using hand radiographs and 0.74 (strong) using LDSS. Kappa for SMSS was 0.66 (strong) using hand radiographs and 0.45 (moderate) using LDSS. Kappa for PHOS was 0.51 (moderate) using LDSS. Intraobserver agreement between LDSS and hand imaging averaged 0.78 (strong) for TOCI and 0.34 (weak) for SMSS.
CONCLUSION: Skeletal maturity assessment with TOCI using LDSS demonstrates strong interobserver reliability when hands are placed at the patient's side and correlates well with assessment on hand radiographs. TOCI achieved better inter- and intraobserver reliability compared to SMSS and PHOS, likely because the thumb readily assumes a good position in standing scoliosis sterioradiographs. LEVEL OF EVIDENCE: Diagnostic-Level III.