Restoration of the degenerated cervical intervertebral space: how much should we distract? A magnetic resonance imaging study

The aim of the study was to quantify normal cervical disc space measurements and to generate a normal values' database. Furthermore, during operative restoration of a degenerated intervertebral disc, it is difficult to calculate the amount of distraction required to restore the collapsed space to its normal height. A secondary purpose is personalizing the anatomical correction. Therefore, we expressed disc height based on measurements of its neighboring disc as an equation, by using simple linear regression. We reviewed MRI studies from asymptomatic healthy subjects (16 men-24 women, mean age 27.25 years). We measured midsagittal anterior, middle and posterior vertebral body and disc height, and disc diameter from C3 to T1 vertebra. We calculated mean disc height, disc height index (DHI) and disc convexity index per spinal level. C6-7 mean and anterior disc height were significantly greater than all respective measurements, except C5-6 (p<0.01). Middle C6-7-disc height was significantly greater compared to respective measurements in every other level (p<0.01). C5-6, C6-7 and C7-T1 mean disc height is significantly greater in men. Middle disc height is the greatest among disc heights in every spinal level. DHI does not differ between sexes, it increases from C3-4 to C5-6 with a slight decrease in C6-7, while its value significantly decreases in C7-T1 (p<0.0001). These measurements could be used for anatomical, individualized restoration of the degenerated intervertebral disc; thus, avoiding overdistraction. Our data could improve preoperative templating or implant design.