Cervical Kinematics After Fusion and Bryan Disc
Rick C. Sasso, MD and Natalie M. Best, BS
Introduction: Disc arthroplasty has been shown to provide short-
term clinical results that are comparable with those attained
with traditional anterior cervical discectomy and fusion. One
proposed benefit of arthroplasty is the ability to prevent or delay
adjacent level operations by retaining motion at the target level
and eliminating abnormal adjacent activity. This paper com-
pares motion parameters for single-level anterior cervical
discectomy and fusion and disc replacement patients at the
index level and adjacent segments.
Methods: Radiographic data from patients enrolled in a
prospective, randomized clinical trial were selected for kinematic
assessment of cervical motion. All patients received either a
single-level fusion with allograft and anterior cervical plate
(Atlantis anterior cervical plate, n=13) or a single-level
artificial cervical disc (Bryan Cervical Disc prosthesis, n=9)
at either C5/C6 or C6/C7. Flexion, extension, and neutral lateral
radiographs were obtained preoperatively, immediately post-
operatively, and at regular intervals up to 24-month time points.
Cervical vertebral bodies were tracked on the digital radio-
graphs using quantitative motion analysis software (QMA,
Medical Metrics) to calculate the functional spinal unit motion
parameters including range of motion (ROM), translation, and
center of rotation. If visible, the functional spinal unit
parameters were obtained at the operative level, and also the
level above and the level below.
Results: As expected, significantly (P<0.006 at 3, 6, 12, and
24mo) more flexion/extension motion was retained in the disc
replacement group than the plated group at the index level. The
disc replacement group retained an average of 6.7 degrees at 24
months. In contrast, the average ROM in the fusion group was
2.0 degrees at the 3-month follow-up and gradually decreased to
0.6 degrees at 24 months. The flexion/extension ROM both
above and below the operative level was not statistically
different for the disc-replaced and fusion patients, however,
mobility increased for both groups over time. The anterior/
posterior translation that occurs with flexion/extension motion
remained unchanged for the disc replacement group at the level
above the target disc preoperatively and postoperatively. In
contrast, the translation increased for the level above the fusion.
At the 6-month follow-up, the increase in translation was
significantly greater for patients that were fused (P<0.02) than
for patients that received a disc replacement. This change was
not significant at 12 months.
Discussion: Previous studies have shown the Bryan disc to
maintain mobility at the level of the prosthesis. The long-term
clinical benefit of maintenance of motion is postulated to be the
ability to delay or avoid adjacent level operations. This study
reveals that there is no difference in flexion/extension ROM at
the level above and below either a fusion or Bryan arthroplasty.
There is, however, an increase in anterior/posterior translation
at the cephalad adjacent level in patients with arthrodesis while
the Bryan arthroplasty retains normal translation for the same
amount of flexion/extension at the adjacent level.
Conclusions: The Bryan disc may delay adjacent level degenera-
tion by preserving preoperative kinematics at adjacent levels.
Key Words: cervical spine, kinematics, arthroplasty, artificial
disc, Bryan artificial disc replacement, fusion
(J Spinal Disord Tech 2007;00:000–000)
and myelopathy.1Because of limitations specific to this
procedure, investigators have developed alternatives to
fusion that attempt to address the kinematic and
biomechanical issues inherent in fusing a cervical motion
Adjacent segment degeneration requiring reopera-
tion has been documented at a rate of 2.9% of patients
per annum by Hilibrand et al.2Other reports have helped
to shed light on the recurrence of neurologic symptoms
and degenerative changes adjacent to fused cervical
levels.2–5In patients undergoing cervical fusion, 25% will
have new onset of symptoms within 10 years of that
fusion.2Segments adjacent to a fusion are subjected to an
increased range of motion (ROM) and increased intra-
Intervertebral disc replacement is designed to
preserve motion, avoid the limitations of fusion, and
allow patients to quickly return to routine activities. It
avoids the morbidity of bone graft harvest,10,11pseudar-
throsis, complications of anterior cervical plating, and the
side effects of cervical immobilization.
nterior cervical discectomy and fusion (ACDF) is a
proven intervention for patients with radiculopathy
CE: jeyasriED: geethaOp: vpBSD:200297
Copyrightr2007 by Lippincott Williams & Wilkins
Received for publication June 16, 2006; accepted February 12, 2007.
From the Indiana Spine Group and Indiana University School of
Medicine, Indianapolis, IN.
Reprints: Rick C. Sasso MD, Clinical Orthopaedic Surgery, Indiana
University School of Medicine, Indiana Spine Group, 8402 Harcourt
Rd., Suite 400, Indianapolis, IN 46260 (e-mail: rsasso@indianaspi-
J Spinal Disord Tech?Volume 00, Number 00, ’’ 2007