Craniofacial morphology and hyoid bone position in neutral and forward head posture: a comparative study in healthy individuals and patients with unilateral anterior disc displacement without reduction

The influence of head posture on craniofacial morphology and hyoid bone position remains insufficiently understood, particularly in patients with unilateral anterior disc displacement without reduction (ADDwOR) under standardized conditions. To investigate posture-dependent and disease-specific differences in craniofacial and hyoid morphology between neutral head posture (NHP) and forward head posture (FHP). In this cross-sectional study, 42 patients with unilateral ADDwOR and 40 healthy controls underwent lateral cephalometry in standardized NHP and FHP using a custom fixation device. Craniocervical, hyoid, and craniofacial variables were analyzed, and their associations with ADDwOR were evaluated using regression models. Associations with ADDwOR were assessed using multivariable logistic regression, and discriminative performance was evaluated via receiver operating characteristic (ROC) analysis. Transition from NHP to FHP induced significant alterations in all craniocervical parameters in both groups ( p < 0.01), confirming a consistent postural effect. However, a key discriminative finding was that the hyoid-to-C3 distance (Hy–cv3ia) remained stable in healthy individuals but was persistently reduced in ADDwOR patients ( p < 0.01), suggesting reduced postural adaptability of the hyoid–cervical relationship. ADDwOR patients also exhibited a characteristic craniofacial pattern, including reduced C1–C2 distance, increased vertical skeletal divergence (FMA, Y-axis) ( p < 0.05). These features were significantly associated with ADDwOR in regression analyses. These findings suggest that patients with unilateral ADDwOR exhibit distinct craniofacial and hyoid characteristics across different postural conditions. Further longitudinal studies are required to determine whether these features represent predisposing factors or consequences of the disorder. Current Controlled Trials ChiCTR2000033328, Reg Date 2020-05.