Optimal chin-brow vertical angle for sagittal visual fields in ankylosing spondylitis kyphosis

Chin-brow vertical angle (CBVA) is very important in correction of thoracolumbar kyphotic deformity in ankylosing spondylitis (AS), especially for the patients with cervical ankylosis. In previous study, Suk et al. stated that the patients with CBVA between −10° and 10° had better horizontal gaze. Unfortunately, in our clinical practice, we found the patients with CBVA between −10° and 10° after surgery usually complained of difficulty in cooking, cleaning, desk working and the like, although they had excellent horizontal gaze. In other words, for the patients with cervical ankylosis, good horizontal gaze existed together with poor downward gaze. Then, which condition do the patients prefer? Is there a compromise solution that makes a better quality life possible for the patients? In this research, we studied AS patients with cervical ankylosis, aiming to investigate the optimal CBVA for deformity correction.

25 AS thoracolumbar kyphotic patients with cervical ankylosis were studied, whose function and expectation of visual field related to life quality were assessed by questionnaire before and after surgery. Pre- and post-operative CBVA were obtained on lateral photos of the patients with free-standing posture, and 50 cases of CBVA were included, which were divided into six groups according to the angle irrespective of surgery (Group A, CBVA <0°; Group B, 0° ≤ CBVA < 10°; Group C, 10° ≤ CBVA < 20°; Group D, 20° ≤ CBVA < 30°; Group E, 30° ≤ CBVA < 40°; Group F, CBVA ≥ 40°). Kruskal–Wallis test was used to assess all the groups in terms of various items in the questionnaire, while Mann–Whitney test was used to assess every two groups.

In overall evaluation, Group C (10°–20°) obtained the optimal expectation (p < 0.05); Group B, C and D (0°–30°) obtained better function (p < 0.05), and there was no significant difference between the 3 groups. In appearance, Group A, B and C (<20°) were better than the other groups both in function and expectation (p < 0.05), without dramatic difference among the three groups. In outdoor activities, Group A, B, C and D (<30°) were better in most of the items (p < 0.05). In indoor activities, Group C and D (10-30°) were much better (p < 0.05).

AS thoracolumbar kyphotic patients with cervical ankylosis had the best satisfaction when 10° ≤ CBVA < 20°.