Journal of Spinal Disorders & Techniques vol:67 issue:3 pages:679-687
In a radiographic study, postoperative segmental alignment was compared between two cohorts of 20
consecutive patients operated with a Bryan Cervical Disc Prosthesis. In group II, patients with severe
preoperative kyphosis were excluded for disc replacement surgery and the surgical technique was
slightly altered in order to avoid asymmetric overdrilling of the posterior part of the cranial endplate of
the caudal vertebral body.
The aim was to investigate whether this change in patient inclusion criteria and this modification of the
surgical technique had an influence on postoperative segmental alignment, and whether postoperative
kyphosis is related to the mechanical properties and/or the design of the prosthesis.
Summary of Background data
Several research groups reported segmental kyphosis after treatment of degenerative disc disease with
the Bryan Cervical Disc Prosthesis.
Based on lateral radiographs, the disc insertion angle (as a postoperative estimate for the
intraoperative angle of approach), and the angle of the functional spinal unit and disc angle (both as
measures for segmental alignment) were calculated.
In group I, 80% of the patients had a kyphotic FSU angle and 40% had a kyphotic disc angle
preoperatively. At follow-up, 65% of the patients had a kyphotic FSU angle while 55% had a kyphotic
disc angle. In group II, 40% of the patients had a kyphotic FSU angle and 5% had a kyphotic disc angle
preoperatively. At follow-up, 40% of the patients had a kyphotic FSU angle while 5% had a kyphotic
Due to the change in patient inclusion criteria, there was a significant difference in preoperative FSU
angle between group I and group II; however no significant difference in preoperative disc angle was
found. Due to the change in surgical technique, the disc insertion angle was significant different
between both groups. A difference in postoperative FSU angle, however nonsignificant, between both
groups was observed. There was a significant difference in postoperative disc angle between both
groups; group I showed significantly more kyphosis of the shells than group II.
This study shows that segmental malalignment with the Bryan Disc can be reduced and is therefore not
device related. Proper patient selection and a modified surgical technique can prevent this adverse