Mandibular slope: a reproducible and simple measure of horizontal gaze

Horizontal Gaze Assessment: An Extensive Narrative Review

OBJECTIVE

Bipedalism was a significant milestone in the evolutionary development of Homo sapiens sapiens, influencing neocortical evolution and subsequent behavioral changes. Coordinated visual and sensory inputs are crucial for posture, environmental interaction, and surgical planning, with horizontal gaze being a pivotal parameter. This narrative review aims to explore various geometric measures used to assess horizontal gaze in patients, highlighting their applications in surgical planning.

METHODS

A literature review was conducted in indexed databases using Mesh terms like "Cervical Vertebrae" and "Visual Fields" along with keywords such as "horizontal gaze" and "sagittal spine parameters." Among 477 initially identified articles, 41 were selected for inclusion after rigorous filtering.

RESULTS

The most recognized method for assessing horizontal gaze is the Chin Brow Vertical Angle (CBVA), initially described in patients with ankylosing spondylitis. Clinical photography is employed as a tool for CBVA calculation, while other measures like McGregor slope and Slope of the Line of Sight have been considered as alternatives to CBVA. Each method presents its unique advantages and limitations.

CONCLUSIONS

This review highlights the need for further research into horizontal gaze measurement methods. Developing novel approaches to determine horizontal gaze can significantly enhance surgical planning and, consequently, improve patient outcomes. The ongoing exploration of these geometric measures offers promising prospects for advancing the field and optimizing patient care.

Association between the Phase Angle and the Severity of Horizontal Gaze Disorder in Patients with Idiopathic Dropped Head Syndrome: A Cross-Sectional Study

Background and Objectives: The phase angle, calculated by bioelectrical impedance analysis, can help elucidate the pathology of patients with idiopathic dropped head syndrome (IDHS) and explain the motor dysfunction associated with the horizontal gaze disorder. The aim of this study was to clarify the characteristics of phase angle in IDHS patients and the relationship between the phase angle and the severity of horizontal gaze disorder. Materials and Methods: This cross-sectional study included 43 female patients with IDHS and 69 healthy female volunteers. A multi-frequency segmental body composition analyzer was used to calculate body composition parameters, including whole-body and lower extremity phase angles. Propensity score (PS) matching analysis was performed to compare the body composition parameters between the IDHS and healthy groups. Variables that determine the PS were identified by correlation analysis, using the whole-body phase angle as the dependent variable. In addition, correlation analysis was performed between the severity of horizontal gaze disorder as assessed by McGregor’s slope (McGS), phase angle, and other body composition parameters. Results: Unadjusted group comparisons showed no significant difference in whole-body and lower extremity phase angles between the IDHS and healthy groups. PS matching created a total of 38 matched pairs for age, height, and fat-free mass index. Although the comparison between groups of matched samples showed no significant difference in the whole-body phase angle, the lower extremity phase angle in the IDHS group was significantly lower than that in the healthy group (p = 0.033). Correlation analysis showed significant negative correlations only between McGS and whole-body (r = −0.31, p = 0.043) and lower extremity phase angle (r = −0.39, p = 0.009) in the IDHS group. Conclusions: Abnormal body composition of the lower extremities were observed in IDHS patients. Furthermore, it was suggested that horizontal gaze disorder in IDHS patients is associated with whole-body and lower extremity phase angles.

Analysis of Parameters That Can Predict the Cervical Sagittal Vertical Axis in Cervical Fusion Surgery

OBJECTIVE

The absolute value of the cervical sagittal parameters cannot be guaranteed with certainty on all follow-up cervical radiographs. With the assumption that neck posture changes can occur at any time at each follow-up radiographic session, we examined whether the sagittal parameters change meaningfully and identified the factors most closely related to the C2-C7 sagittal vertical axis (SVA).

METHODS

We enrolled 200 patients who had undergone either anterior cervical fusion (n = 100) or posterior cervical fusion (n = 100). The craniovertebral angle (CVA), mandible angle (MA), occipital slope (Os), C2 slope (C2s), C7 slope (C7s), and C2-C7 SVA were measured on 2 different follow-up radiographs after surgery. The C2-C7 angle (C2-C7A) and changes (Δ) in the sagittal parameters between the 2 radiographs were then calculated.

RESULTS

The ΔC2s and ΔCVA showed a very strong correlation with the ΔC2-C7 SVA (r = |0.70-0.93|). An independent t test showed a statistically significant difference for multiple sagittal parameters (i.e., ΔMA, ΔOs, ΔC2s, ΔC7s, and ΔCVA) between the large and small ΔC2-C7 SVA groups. In contrast, the change in the C2-C7A was without statistical significance. A stepwise multivariate regression analysis revealed a high adjusted R2 value (0.841) between the ΔC2-C7 SVA and 2 parameters (standardized coefficient: ΔCVA, -0.563; ΔC2s, -0.398).

CONCLUSIONS

During cervical fusion surgery, the CVA was the most predictable parameter reflecting the C2-C7 SVA in various analyses. The upper cervical parameters (Os and C2s) provided more explanatory power regarding the C2-C7 SVA changes than did the lower cervical parameter (C7s) or the presence of cervical lordosis (C2-C7A).

Association between the Horizontal Gaze Ability and Physical Characteristics of Patients with Dropped Head Syndrome

Background and Objectives: Patients with dropped head syndrome exhibit weakness of the cervical paraspinal muscles. However, the relationship between horizontal gaze disorder and physical function remains unclear. This study aimed to examine and clarify this relationship. Materials and Methods: Ninety-six patients with dropped head syndrome were included. We measured the McGregor’s Slope and investigated physical characteristics, including cervical muscle strength, back muscle strength, and walking ability. Factor analysis was used to classify the characteristics of physical function, and a linear multiple regression analysis was used to evaluate independent variables explaining the variance in the McGregor’s Slope. The physical functions of DHS patients were classified into three categories by factor analysis: limb and trunk muscle strength, walking ability, and neck muscle strength. Results: The average value of the McGregor’s Slope was 22.2 ± 24.0 degrees. As a result of multiple regression analysis, walking speed (β = −0.46) and apex (β = −0.30) were extracted as significant factors influencing the McGregor’s Slope. Conclusions: Horizontal gaze disorders are not associated with cervical muscle strength but with the walking ability and the alignment type of dropped head syndrome.