Which parameters are relevant in sagittal balance analysis of the cervical spine? A literature review

Cervical spine is part of the spine with the most mobility in the sagittal plane. It is important for surgeons to have reliable, simple and reproducible parameters to analyse the cervical. This study is a systematic review and a critique of current parameters to help improve the study of cervical spinal balance. We conducted a systematic search of PUBMED/MEDLINE for literature published since January 2014. Only studies written in English and containing abstracts were considered for inclusion. The search performed was: A << C7 slopeA >> OR A << T1 slopeA >> OR A << C2C7 offsetA >> OR A << C2C7 lordosisA >> OR A << cervical SVA (sagittal vertical axis)A >> OR A << TIA (thoracic inlet angle)A >> (Lee et al., J Spinal Disord Tech 25(2):E41-E47, 2012) OR A << SCA (spino-cranial angle)A >>. Exclusion criteria were purely post-operative and cadaveric analysis, studies performed with CT scan or MRI, studies on adolescent idiopathic scoliosis, traumatology studies and no standing analysis of the cervical spine. Relevance was confirmed by investigators if cervical parameters was a major criteria of the study. 138 articles were found by the electronic search. After complete evaluation 20 articles were selected. The large majority of papers used the same parameters C2_C7 lordosis, C2-C7 SVA, T1 slope or C7 slope and T1 slope/cervical lordosis mismatch. Janusz reported a new parameter using a retrospective cohort of patient with cervical radiculopathy: the TIA (thoracic inlet angle). Le Huec reported an other new parameter based on a prospective study of asymptomatic volunteer: the spino-cranial angle (SCA). This parameter is highly correlated with the C7 slope and the cervical lordosis. Other studies reported parameters that are more global balance analysis including the cervical spine than cervical spine balance itself. The most important parameters to analyse the cervical sagittal balance according to the literature available today for good clinical outcomes are the following: C7 or T1 slope, average value 20A degrees, must not be higher than 40A degrees. cSVA must not be less than 40A degrees C (mean value 20 mm). SCA (spine cranial angle) must stay in a norm (83A degrees A +/- 9A degrees). Future studies should focus on those three parameters to analyse and compare pre and post op data and to correlate the results with the quality of life improvement.