MRI-based cervical ring apophysis maturation: a probabilistic approach to legal age thresholds.

The primary question in forensic age assessment is whether an individual has reached a legally defined age threshold. Cervical ring apophysis maturation has been proposed as a potential age indicator; however, it has previously been studied only with ionizing imaging. This study aimed to evaluate cervical ring apophysis maturation using magnetic resonance imaging (MRI) and to determine stage-specific probabilities for legally relevant age thresholds.This retrospective cross-sectional study included 1000 individuals (552 females, 448 males) aged 9.64-26.67 years. Maturation of the ring apophysis at C2-C4 was assessed using a five-stage MRI-adapted system. Sex-specific descriptive statistics were calculated. Age-related stage transitions were modeled using multinomial logistic regression, and conditional probabilities were estimated for the 15-, 16-, 18-, and 21-year thresholds. Observer agreement was assessed using weighted kappa.Maturation progressed sequentially from C2 to C4 in both sexes, with a broad transitional zone between stages 3 and 4. In females, median age at stage 4 ranged from 18.5 to 20.2 years in males, approximately 22 years. However, minimal ages for stage 4 were markedly lower (12.5 years in females, 13.1 years in males), and stage 3 persisted into the third decade. At stage 4, the probability of being ≥ 18 years reached 0.96-0.98 in males but only 0.54-0.61 in females. For the ≥ 21-year threshold, probabilities at stage 4 were approximately 0.65-0.70 in males and 0.34-0.40 in females.Cervical ring apophysis maturation on MRI represents a continuous and overlapping biological process. It should therefore be interpreted as a probabilistic indicator for legal thresholds rather than a definitive test of adulthood.