QUANTIFICATION OF NORMAL MAGNETIC RESONANCE INTERVERTEBRAL SPACE RELATIONSHIPS IN THE SUBAXIAL CERVICAL SPINE: INTRODUCING THE A FACTOR

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Aim. This is a study of normal magnetic resonance anatomy of the subaxial cervical spine and aims at creating database values of each normal intervertebral space. When surgically restoring a degenerated disc, it is difficult to estimate the exact amount of perioperative distraction needed. This study proposes that restoration of a collapsed disc could be based on individual measurements of its adjacent, healthier disc with the aid of baseline values. Material and Methods. We retrospectively reviewed cervical MRIs of 29 asymptomatic subjects (11 men, 18 women, mean age 28,2 years, range 19-40). All intervertebral discs in every subject were grade I or II according to Pfirrmann classification. We measured anterior, middle and posterior disc and vertebral height and disc diameter, and consequently calculated mean disc height, disc convexity index and disc height index (DHI). Inter- and intra-observer agreement has been previously proven to be excellent. Each intervertebral disc height was expressed as a fixed percentage of its adjacent one, the a factor. The height of a collapsed C4-5 could be calculated by the simple equation C4-5=C3-4/a3-4. Results and Discussion. Mean disc height-and DHI was significantly different at every spinal level and increasing from C3-4 to C6-7, anddecreasing from C6-7 to C7-T1 (p<0.01). Similarly, disc diameter increased from C3-4 to C6-7 and then a slight decrease was observed (p<0.05) from C6-7 to C7-T1. Disc was less convex from C3-4 to C5-6, while disc convexity index increased from C6-7 to C7-T1 (p<0.05). We quantified normal relationships of adjacent intervertebral spaces with the use of established radiological indices. Conclusions. We documented the α factor for anterior, posterior and mean height on normal subjects as baseline values for future reference.