Radiological Changes After Craniovertebral Junction Stabilization: Evaluation of Established Measurements and Novel Cranial and Caudal Anterior Atlantodental Interval Parameters

Background/Objectives: Craniovertebral junction (CVJ) stabilization alters complex anatomical relationships that may not be fully characterized by a single radiological parameter. This study evaluated the responsiveness of established CVJ measurements after stabilization and explored the observer reliability and postoperative behavior of separate cranial and caudal anterior atlantodental interval (AADI) measurements. Methods: This retrospective radiological case series included 26 patients who underwent CVJ stabilization between 2000 and 2022. Eleven parameters were measured on preoperative and immediate postoperative mid-sagittal computed tomography (CT) reconstructions by two independent observers, each completing two measurement sessions, with each observer blinded to the other observer’s measurements and to his own previous session. Reliability was evaluated using intraclass correlation coefficients (ICCs), and paired comparisons were adjusted using the Benjamini–Hochberg procedure. Results: Postoperative reductions were observed in odontoid distances from the Chamberlain (q = 0.019), McGregor (q = 0.040), and McRae lines (q = 0.019). Cranial AADI decreased from 5.66 ± 3.31 to 4.17 ± 2.44 mm (q = 0.009), and caudal AADI decreased from 4.81 ± 2.98 to 3.57 ± 2.32 mm (q = 0.019). However, the within-patient cranial–caudal difference score did not change significantly after stabilization (mean change, −0.25 mm; 95% CI, −0.96 to 0.47; p = 0.472; Cohen’s dz = −0.19). Intraobserver ICCs ranged from 0.880 to 0.987, while single-measure interobserver ICCs ranged from 0.784 to 0.899. Conclusions: Established craniometric distances and separate cranial and caudal AADI measurements demonstrated postoperative radiological changes with good-to-excellent observer reliability. In this cohort, segmented AADI and angular parameters showed different patterns of postoperative change; however, their relative responsiveness was not directly compared. Segmented AADI should currently be regarded as an exploratory radiological parameter, as its diagnostic thresholds, clinical validity, and association with patient outcomes have not yet been established.