Three novel orbito-cervical parameters: highly repeatable and simple measurements of horizontal gaze

The purpose of this single centre radiographic study on healthy volunteers was to evaluate three novel orbito-cervical parameters in a population of healthy volunteers and calculate the observer agreements and errors for these parameters.

The cohort comprised 126 healthy adult volunteers, 88 females and 38 males, aged 33.6 ± 12.0, with full-spine sagittal radiographs and no history of back and/or neck pain, spine and/or lower limb pathologies, or spine and/or hip surgeries. The following were measured on radiographs: C1-slope (C1S), orbito-cervical tilt (OCT), orbito-cervical incidence (OCI), chin-brow vertical angle (CBVA), McGregor's slope (McGS), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). Pearson's correlation coefficients were calculated between all radiographic measurements.

C1S was 9.8 ± 6.6°(range, 0.1-29.1), OCT was 66.7 ± 6.9°(range, 48.7-82.0), and OCI was 75.9 ± 7.2°(range, 52.5-89.8). All measurements had excellent observer agreements (ICC > 0.900) and low observer errors (MAE < 2.5). OCI strongly correlated with C1S + OCT (r = 0.95, p < 0.001). OCT strongly correlated with McGregor's slope (r = - 0.78, p < 0.001), moderately correlated with CBVA (r = 0.64, p < 0.001), but weakly correlated with OCI (r = 0.46, p < 0.001). C1S moderately correlated with OCT (r = - 0.51, p < 0.001), OCI (r = 0.5, p < 0.001), CBVA (r = - 0.52, p < 0.001), and McGregor's slope (r = 0.64, p < 0.001).

OCI is strongly correlated with C1S + OCT and these orbito-cervical parameters are to some extent correlated with existing sagittal cervical parameters. Furthermore, they have excellent observer agreements (ICC > 0.900) and low inter- and intra- observer errors (MAE < 2.5). The authors recommend the use of these orbito-cervical parameters in clinical practice to provide a better understanding of horizontal gaze, leading to improved preoperative planning for spinal fusion.