Influence of cervical spine position on the radiographic parameters of the thoracic inlet alignment

Cervical sagittal balance is a complex phenomenon, influenced by many factors, which cannot be described by cervical lordosis alone. Attention has been focused on the relationship between T1 slope, thoracic inlet angle, and cervical sagittal balance. However, the effect of cervical position on these parameters has not been evaluated yet. The aim of this study was to assess the influence of cervical flexion and extension on radiographic thoracic inlet parameters. 60 patients with one level radiculopathy symptoms underwent radiological examination. Mean age was 53 (40-72) years; there were 24 males and 34 females. Lateral standing X-rays of cervical spine were taken on the same day in neutral position, full flexion and full extension. Patients with previous cervical operations or congenital malformations were excluded. Thoracic inlet angle (TIA), neck tilt (NT) and thoracic (T1) slope were measured. Agreement between measurements was assessed and quantified by intra-class correlation coefficient (ICC) and median error for a single measurement (SEM). The ICC value greater than 0.75 reflected sufficient agreement. The mean values of the parameters were: (1) for the neutral position: TIA 71.7A degrees A A +/- A 9.5A degrees; T1 slope 26.7A degrees A A +/- A 6.3A degrees; and NT 44.9A degrees A A +/- A 7.2A degrees, (2) In extension: TIA 71.8A degrees A A +/- A 9.4A degrees; T1 slope 24.9A degrees A A +/- A 7.6A degrees; and NT 46.9A degrees A A +/- A 7.2A degrees and (3) In flexion 78.3A degrees A A +/- A 10.3A degrees; T1 slope 33.6A degrees A A +/- A 7.8A degrees; and NT 44.7A degrees A A +/- A 7.4A degrees. An excellent agreement was revealed for all NT measurements (ICC 0.76) and for TIA measured in flexion and neutral position (ICC 0.79). There was insufficient overall and in-pairs agreement for T1 slope measurements. Neck tilt measurements were not influenced by position of the cervical spine. T1 slope was significantly influenced by flexion and extension of the neck. This puts the concept that TIA is a morphologic parameter into question. This information should be taken into consideration when analyzing lateral radiographs of the cervical spine for clinical decision-making.