Thumb Ossification Composite Index (TOCI) for Predicting Peripubertal Skeletal Maturity and Peak Height Velocity in Idiopathic Scoliosis

Abstract

Background:Accurate skeletal maturity assessment is important to guide clinical evaluation of idiopathic scoliosis, but commonly used methods are inadequate or too complex for rapid clinical use. The objective of the study was to propose a new simplified staging method, called the thumb ossification composite index (TOCI), based on the ossification pattern of the 2 thumb epiphyses and the adductor sesamoid bone; to determine its accuracy in predicting skeletal maturation when compared with the Sanders simplified skeletal maturity system (SSMS); and to validate its interrater and intrarater reliability.Methods:Hand radiographs of 125 girls, acquired when they were newly diagnosed with idiopathic scoliosis prior to menarche and during longitudinal follow-up until skeletal maturity (a minimum of 4 years), were scored with the TOCI and SSMS. These scores were compared with digital skeletal age (DSA) and radius, ulna, and small hand bones (RUS) scores; anthropometric data; peak height velocity; and growth-remaining profiles. Correlations were analyzed with the chi-square test, Spearman and Cramer V correlation methods, and receiver operating characteristic curve analysis. Reliability analysis using the intraclass correlation (ICC) was conducted.Results:Six hundred and forty-five hand radiographs (average, 5 of each girl) were scored. The TOCI staging system was highly correlated with the DSA and RUS scores (r = 0.93 and 0.92, p < 0.01). The mean peak height velocity (and standard deviation) was 7.43 ± 1.45 cm/yr and occurred at a mean age of 11.9 ± 0.86 years, with 70.1% and 51.4% of the subjects attaining their peak height velocity at TOCI stage 5 and SSMS stage 3, respectively. The 2 systems predicted peak height velocity with comparable accuracy, with a strong Cramer V association (0.526 and 0.466, respectively; p < 0.01) and similar sensitivity and specificity on receiver operating characteristic curve analysis. The mean age at menarche was 12.57 ± 1.12 years, with menarche occurring over several stages in both the TOCI and the SSMS. The growth remaining predicted by TOCI stage 8 matched well with that predicted by SSMS stage 7, with a mean of <2 cm/yr of growth potential over a mean of <1.7 years at these stages. The TOCI also demonstrated excellent reliability, with an overall ICC of >0.97.Conclusions:The new proposed TOCI could provide a simplified staging system for the assessment of skeletal maturity of subjects with idiopathic scoliosis. The index needs to be subjected to further multicenter validation in different ethnic groups.

Validation Study of the Thumb Ossification Composite Index (TOCI) in Idiopathic Scoliosis

“…The hand radiographs illustrate the TW3 stage (linked by dotted lines) of the corresponding epiphyses shown in the respective bar charts. The letters B through I on the drawings of the thumb refer to the key radiographic features of maturity indicators represented by the different TOCI stages described in our previous article 4 .The diagram at the upper right (viii) is included for easier referencing to the corresponding growth phase at puberty. DP, MP, and PP = distal, middle, and proximal phalangeal, and MC = metacarpal.…”

“…Thus, a new simplified guideline for interchangeable use of the SSMS and TOCI (Fig. 5 ; also see Video 1 in our previous study 4 ) to assess and predict the state of skeletal maturity in the peripubertal period, including the timing of peak height velocity and growth remaining, can be formulated.…”

“…The present study included a previously reported cohort 4 of 125 skeletally immature girls with idiopathic scoliosis who had been followed at a minimum of 5 intervals averaging 6 months each during the peripubertal growth period until skeletal maturity was confirmed by radiographic evidence of completed physeal closure of the distal radial epiphysis. At each visit, posteroanterior radiographs of the left hand were obtained with use of the original TW3 protocol.…”

“…Correlation analysis was conducted to (1) determine the probability of TOCI and TW3 staging of the thumb epiphyses predicting the TW3 status (stages E through I) of the epiphyses of the ulnar 4 digits and (2) carry out a stage-to-stage comparison of the TOCI and SSMS at different periods relative to the timing of peak height velocity (6 to 12 months before peak height velocity, at peak height velocity, and ≥12 months after peak height velocity) as determined from a previous study 4 .…”

“…We have found the new simplified thumb ossification composite index (TOCI), based on ossification of the thumb epiphyses and adductor sesamoid, to be simple to use, with excellent reliability and accuracy in predicting skeletal maturity of patients with idiopathic scoliosis 4 .…”