Long-term follow-up of movement of the cervical spine after anterior cervical discectomy (ACD) or anterior cervical discectomy with arthroplasty (ACDA)

Cervical degenerative disc disease (CDDD) results from degeneration of cervical
intervertebral disc(s) and/or the adjoining vertebral bodies. This causes
clinical symptoms of cervical myelopathy, radiculopathy or myeloradiculopathy.
Surgical treatment can be an option if non-surgical treatment options provide
insufficient relief. The standard surgical technique for treating single or
multilevel CDDD is anterior cervical discectomy, either without (ACD) or with
fusion (ACDF). Both ACD and ACDF have good short-term clinical results in
90-100% of patients. Both techniques also have a high rate of fusion,
respectively 70-80% and 95-100% 1. After 7-20 years, patient satisfaction
slowly drops to 68-96% 2. The reason for this decline is thought to be due to
the development of adjacent segment disease (ASDis). This is defined as the
development of new complaints of radiculopathy or myelopathy due to
degeneration one level above or below the previously operated segment. This
occurs in approximately 25% of patients during 10 years follow-up and more than
2/3 of these patients need additional surgery 3. The underlying mechanism is
thought to be compensation of loss of motion in the fused segment, resulting in
overstraining of the adjacent segments 4. Anterior cervical discectomy with
arthroplasty (ACDA) is developed in an effort to reduce the incidence of ASD by
preserving physiological motion in the operated segment.

Although the term *physiological motion* is commonly used, a proper definition
has been lacking for a long time. Segmental range of motion (sROM, e.g. the
amount of sagittal rotation in a segment between maximal flexion and maximal
extension position of the entire cervical spine) is most commonly used to study
motion. SROMs, however, suffer from large intra- and interindividual
variability 5,6. Therefore, in the lower cervical spine, Boselie et al have
recently described a consistent sequence of segmental contribution in sagittal
rotation during flexion and extension in 20 healthy participants 7,8. This was
based on historic reports by van Mameren et al 5,6. The mean age of the healthy
participants was 23 years (SD 2.65, range 18-55 years). They showed that the
sequence of segmental contributions in the lower cervical spine during the
second half of extension of the entire cervical spine and head was uniform in
80-90% of the healthy participants. The sequence of segmental contributions was
C4-C5 followed by C5-C6, and then C6-C7. Also, they described a group of ten
single level cervical degenerative disc disease (CDDD) patients in which this
sequence was present in only one patient (10%) 7. This is the first method
described which can reliably differentiate between normal or abnormal movement
of the cervical spine in an individual subject.

Moreover, Boselie et al performed a randomized controlled trial (RCT) to
compare the presence of this physiological motion pattern and clinical outcomes
for ACDA (n=12) and ACD (n=12) patients. Before the randomization 3 patients
were operated in a pilot group (all with ACDA), so in total 27 patients with
CDDD and radiculopathy were operated. In both groups 10 patients were available
for follow-up at one year and fusion rate was 0% in the ACDA group and 70% in
the ACD group. The majority of patients in the ACDA group (80%) showed a normal
sequence of segmental contribution of motion. There were no differences in
patient reported outcome measures, however the study population was small.
These data have been submitted but not been published yet since follow-up
duration is considered to short for most journals. The primary goal at the
moment was to analyze sequence of segmental contribution of motion for which a
follow-up duration of one year seemed appropriate. It was also common for this
type of study at the moment the study was started. However, the expected
advantage of the ACDA lies in the long-term since it should lead to less ASD by
preserving physiological motion in the operated segment. Therefore, longer
follow-up is needed to be able to determine if this physiological pattern
remains present in the majority of the ACDA group in the long term.

Several RCT*s have been published in the past 10 years to assess the effects of
ACDA versus ACD or ACDF in the treatment of cervical radiculopathy/myelopathy
due to single level CDDD. A Cochrane review of 9 studies with a total of 2400
included patients were analyzed, the results for the ACDA group were better
than the ACDF group for all comparisons after 1-2 years. However, the actual
differences in effect were small and not clinically relevant for any of the
primary outcomes 9. More recently, long-term results of the previously
mentioned RCT*s are being published. The ACDA group shows better results on
neck complaints and a lower amount of re-operations at adjacent levels 10.

In the RCT performed by Boselie et al, the first patient was operated in
December 2007 and the last one patient in September 2014. At this moment the
follow-up duration is therefore 6 to almost 13 years. Our method for analyzing
the sequence of segmental contribution of motion and to differentiate between
normal or abnormal movement 8 has not been used before in long-term follow up
of CDDD patients who underwent surgery. Therefore, we want to analyse the
movement of the cervical spine in these 27 patients again in the long-term (at
an average follow up of 9 years). We hope to be able to define a different
movement pattern in patients undergoing ACD or ACDF. We expect to see an
increase in motion on the levels adjacent to the operated segment. This might
support our hypothesis of the development of ASD after fusion surgery.

The primary objective of this study is to investigate the sequence of segmental
contributions in the cervical spine in the long-term follow-up of surgery for
CDDD. Specifically, the motion of the cervical spine after ACD and ACDA will be
analyzed compared to the short-term follow-up at one year after surgery.
The secondary objectives will be to correlate these motion patterns to the
long-term clinical outcome of the long-term follow-up of these patients.
Clinical outcomes will be assessed according to the visual analogue score (VAS)
score for neck and arm pain, the neck disability index (NDI), SF-36 and Odom
Outcome Score.
Moreover, patients will be asked to indicate whether they have been diagnosed
with new episodes of CDDD and if/how these were treated.
All patients will undergo a clinical neurological exam to assess clinical
outcomes.
Moreover, the degree of degeneration will be determined on lateral X-rays of
the cervical spine and scored according to the Kellgren classification.

This is a fundamental research project in which a cohort of previously operated
patients will be included. All of these patients were previously operated in
the setting of a randomized controlled trial. Initial flexion and extension
cinematographic recordings of the cervical spine have been made before surgery,
and at three months and one-year post-operatively. We will now make similar
cinematographic recordings to assess the long-term changes in cervical
segmental range of motion in this group of patients having undergone ACD or
ACDF.
Participants have previously indicated that they are open to be contacted for
follow-up studies. They will be asked to participate in this study through a
phone call, after which an information letter will be sent to them. Informed
consent will be signed after a reflection period of at least 7 days, if they
are willing to participate.

Flexion- and extension cinematographic recordings are made using the Philips
Allura Xper FD20 X-ray system. Radiation dose per cinematographic recording,
determined by radiation experts, will be around 0.084 mSv. A lateral X-ray of
the cervical spine will be made to asses fusion on the operated segment and
degeneration at adjacent levels (according to the Kellgren*s classification),
resulting in a radiation dose of 0.0096 mSv. Average radiation dose per
participant will therefore be 0.0938 mSv.
This amount of radiation can be categorized in category IIa using the
Neurocritial Care Society (NCS) guidelines about risk of radiation dosage
(0.1-1mSv) [Dosimetry NCOr). This category includes moderate risk which can be
justified if there is a potential health benefit for future patients.