Ideal dimensions of a cervical disc arthroplasty implant: Can one width fit all?

To determine the normal inter-uncinate distance (IUD) across subaxial disc spaces and compare that to the width dimensions of currently marketed cervical disc arthroplasty (CDA) devices.

Cervical spine CT scans from a convenience sample of 50 healthy patients (29 males, 21 females), aged 23-28 years, for negative trauma evaluations were utilized. The normative reference values on the SEP of subaxial vertebrae (C4-C7) were obtained by measuring the IUD across two different reference points: uncinate base (A1, A2, A3) and between the uncinate process tips (B1, B2, B3) on coronal reconstructions at three disc-space depths (anterior-1/3rd, ½-point, posterior-1/3rd).

The mean-IUD at posterior-1/3rd-base (A3) was the limiting width at all levels, which only increased from 11.3 ± 2 mm at C4-13.4 ± 2.9 mm at C7. A1 and A2 were both greater than 14 mm in the majority at all levels; C4-50%, C5-56%, C6-72%, C7-90%; whereas A1 and A2 were rarely > 17 mm (most contacted CDA-width): C4-2%, C5-4%, C6-16%, 44%-C7. There was no statistically significant difference in mean-A3 at any of the levels (all p > 0.05), based on sex or BMI category.

IUD increases from cephalad to caudad and reduces from anterior to posterior at each level. For the vast majority (regardless of gender/BMI), the IUD is at least 14 mm, especially in the most commonly CDA-treated disc spaces (C5-6, C6-7), suggesting that 14 mm could serve as "one-width" for all CDAs, especially if the primary goal of the surgical technique is to significantly reduce the need for bony resection/burring to create a proper width-fit of the implant.