Thoracic inlet angle
The TIA is formed where the T1 vertical line of the upper endplate (from the center of the T-1 upper endplate) meets with the line formed between the upper end of the manubrium and the center of the T-1 upper endplate. Several published papers confirmed that T1 slope and the other cervical parameters are highly correlated with cervical sagittal balance 1) 2)
Schematic drawing of the measured angles of the cervicothoracic spine segments. a: Neck tilt; b: T1 slope; c: Thoracic inlet angle; d: C2 C7 angle.
1)
Vital JM, Senegas J. Anatomical bases of the study of the constraints to which the cervical spine is subject in the sagittal plane. A study of the center of gravity of the head. Surg Radiol Anat. 1986;8(3):169–73.
2)
Wang ZL, Xiao JL, Mou JH, et al. Analysis of cervical sagittal balance parameters in MRIs of patients with disc-degenerative disease. Med Sci Monit. 2015;21:3083–88.