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Effects of Advanced Age on the Morphometry and Degenerative State of the Cervical Spine in a Rat Model.

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THE ANATOMICAL RECORD 294:1326–1336 (2011)
Effects of Advanced Age on the
Morphometry and Degenerative State of
the Cervical Spine in A Rat Model
ANDREW C. LAING,1* RILEY COX,2 WOLFRAM TETZLAFF,3,4
4,5
AND THOMAS OXLAND
1
Injury Biomechanics and Aging Laboratory, Department of Kinesiology,
University of Waterloo, Waterloo, Ontario, Canada
2
School of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby,
British Columbia, Canada
3
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
4
International Collaboration on Repair Discoveries (ICORD), Vancouver,
British Columbia, Canada
5
Orthopaedics and Injury Biomechanics Group, Departments of Orthopaedics and Mechanical
Engineering, University of British Columbia, Vancouver, British Columbia, Canada
ABSTRACT
Aging causes changes in the geometry of the human cervical spine that
may influence the tissue response to applied loads. Rat models are often used
to study spinal cord injuries (SCI) and have the potential to enhance our
understanding of the effect of age on SCI. The goal of this study was to characterize the morphometry and degenerative state of the cervical spine in
Fisher 344 rats, and to determine the influence of age on these variables. Fifteen rats were split into three age groups: young adult (3 months of age),
aged (12–18 months) and geriatric (30 months). Following tissue harvest we
used a lCT scanner to image the cervical and upper thoracic spine from each
specimen. Analysis software was used to measure variables including canal
pinch diameter (the most rostral point on the dorsal aspect of a vertebral
body to the most caudal aspect of the lamina on the immediately rostral vertebra), vertebral canal depth, width, and area, vertebral body height, depth,
width, and area, and intervertebral disc thickness. Orthopaedic surgeons
used midsagittal images to rate the degenerative state of the intervertebral
discs. For all measures except disc thickness there was a significant increase
(mean (SD) ¼ 15.0 (9.7)%) for the aged compared to young specimens (P <
0.05). There were significant differences between the aged and geriatric
specimens for only vertebral body depth (P ¼ 0.016) and area (P ¼ 0.020).
Intervertebral disc degeneration was significantly greater on the ventral aspect of the spinal column (P < 0.001), with a trend toward increased degeneration in the geriatric specimens (P ¼ 0.069). The results suggest that agerelated morphometric differences may need to be accounted for in experiC 2011
mental aging models of SCI in rats. Anat Rec, 294:1326–1336, 2011. V
Wiley-Liss, Inc.
Key words: spine; age; rat; morphometry; degeneration; cervical
Grant sponsor: The Natural Sciences and Engineering
Research Council of Canada (NSERC); Grant sponsor:
Christopher and Dana Reeve Foundation; Grant number: LB10801-2.
*Correspondence to: Andrew C. Laing, Department of Kinesiology, University of Waterloo, 200 University Ave West, WaterC 2011 WILEY-LISS, INC.
V
loo, Ontario, Canada N2L 3G1. Fax: 519-746-6776.
E-mail: [email protected]
Received 7 July 2010; Accepted 26 March 2011
DOI 10.1002/ar.21436
Published online 28 June 2011 in Wiley Online Library
(wileyonlinelibrary.com).
EFFECTS OF AGE ON SPINE MORPHOMETRY IN RATS
INTRODUCTION
There are approximately 12,000 new cases of spinal
cord injury (SCI) in North America each year (O’Connor,
2006; NSCISC, 2010). Because of the chronic nature of
many of these injuries, the lifetime medical costs typically range between $500,000 and $5,000,000 per case,
whereas the total economic cost (including medical care
and lost wages) is estimated in the tens of billions of dollars per year in North America alone (Priebe et al.,
2007). Even more important are the effects of SCI on
personal suffering and decreased quality of life.
Because of the aging of the population in most developed nations, the incidence of SCI in elderly persons is
growing faster than in any other age group (similar to
the trends for other fall-related injuries such as hip fractures) (Nobunaga et al., 1999; Kannus et al., 2000;
O’Connor, 2006; Kannus et al., 2007). For example in
the province of Ontario in Canada, those 65 years of age
and older have a higher rate of SCI than the 20–39 year
group, leading to a bimodal age profile for SCI (Pickett
et al., 2003; Pickett et al., 2006). The prevalence of
comorbidities before SCI is significantly higher for elderly versus young persons, and secondary complications
after SCI are more frequent among individuals with preexisting medical conditions (Krassioukov et al., 2003).
In light of the epidemiologic evidence which demonstrates the high incidence of SCI in elderly persons
(Nobunaga et al., 1999; Kannus et al., 2000; Pickett
et al., 2003; O’Connor, 2006; Pickett et al., 2006; Kannus
et al., 2007), one significant limitation of our understanding of these injuries is that the vast majority of experimental studies have been conducted with young
animal specimens. To date, only five studies have investigated the potential influence of advanced age on SCI
by investigating rats greater than 12 months of age
(rats have a lifespan of over 2 years). Genovese et al.
(2006) found that following spinal cord clip compression,
18-month old rats suffered more severe trauma than 3month old rats characterized by increased edema and
neutrophil infiltration (based on myeloperoxidase staining), increased immunoreactivity for nitrotyrosine,
decreased motor test scores Basso, Beattie, Bresnahan
(BBB) Locomotor Rating Scale, and a higher mortality
rate. Following spinal hemisection, Gwak et al. (2004)
reported that 12-month old rats demonstrated greater
locomotor deficits (BBB, paw withdrawal latency) than
40 and 60-day old rats. Chaovipoch et al. (2006) inferred
a protracted time course of cell death following complete
crush atT8–9 in 12-month compared to 2-month old rats,
based on the number of TUNEL positive (apoptotic) cells
in the gray matter. Finally, Siegenthaler et al. (2008a;
2008b) reported that following thoracic spinal cord contusion injuries, 12 (aged) and 30-month old (geriatric)
rats showed less spontaneous recovery of walking,
slower bladder function recovery, greater demyelination
and less remyelination than 3-month old rats. Each of
these studies demonstrated a significant influence of
age. However, to provide more insights into the factors
underlying these differences we require enhanced knowledge of the age-related changes in uninjured rats.
Although age-related changes in vertebral column
morphology may have little influence on spinal cord tissue damage during injury mechanisms such as clip compression, hemisection, or crush, they could potentially
1327
play a substantial role during more clinically relevant
injury mechanisms including contusion (simulating a
burst fracture) (Scheff et al., 2003) or fracture-dislocation (caused by relative shearing of two adjacent vertebral bodies) (Choo et al., 2007; 2008). For example, if the
vertebral canal is significantly larger in older rats, a
given vertebral dislocation displacement would cause
less relative shearing of the spinal cord than in young
animals. Consequently, to confidently apportion the
cause of age-related tissue damage following SCI to
structural versus physiological pathway differences,
characterization of these factors in healthy animals
across a range of ages is required.
As the vast majority of SCI in older adults occur in
the cervical as opposed to thoracic region (Nobunaga
et al., 1999; Pickett et al., 2006), there is a clear need
for experimental animal models that investigate agerelated differences in cervical SCI. However, very little
is known about how advanced age influences the morphometry of the rat cervical spine. Flynn and Bolton
(2007) produced some of the only quantitative data on
cervical vertebral canal dimensions in rats. Similar to
the trend in Caucasian humans (Tatarek, 2005), they
reported that the anterior–posterior (AP) depth of the
canal tended to decrease from C2 (avg (SD) ¼ 3.62 (0.31)
mm) to T1 (avg (SD) ¼ 2.59 (0.13) mm). In contrast,
mediolateral dimensions were smallest at the C2 level
(avg (SD) ¼ 4.13 (0.27) mm) and progressively increased
at more caudal segments (C7 avg (SD) ¼ 5.17 (0.19)
mm). Unfortunately, their experimental protocol did not
allow for the calculation of several important variables
that influence spinal cord injury and cervical myelopathy. Specifically, by separating each vertebra and removing all soft tissues during dissection, variables measured
across vertebral segments [e.g., canal pinch diameter
(CPD) (Ivancic et al., 2006)] and markers of spine degeneration (including osteophyte development and changes
to the intervertebral disc) could not be quantified. An
important unanswered question is whether such morphometric measures would differ as a function of age in
adult rats.
The objectives of this study were twofold. Our first
aim was to use a custom-developed micro-computed tomography collection and analysis procedure to determine
the influence of age on the morphometry of the cervical
vertebral column in rats. The second aim was to determine whether the degree of cervical intervertebral disc
degeneration inferred from radiographs, as assessed by
orthopaedic surgeons, was influenced by rat age. These
data will aid in determining whether rats are a suitable
model to assess age-related changes in the cervical
spine, and will assist in interpreting the results from
studies that use a rat model to assess the influence of
age on the response of the spinal cord to mechanical
assault.
MATERIALS AND METHODS
Tissue Specimens
Tissue harvest involved anaesthetization with isoflurane followed by transcardial perfusion with warm saline
and then ice-cold 4% paraformaldehyde with 0.25% glutaraldehyde, at which point the cervical/upper thoracic
spinal columns were removed from 15 male Fisher 344
rats. We selected this strain of rat for our aging studies
1328
LAING ET AL.
as they weigh less than Sprague-Dawley rats, and have
successfully been used as an aging animal model in
nerve regeneration studies (Apel et al., 2009; Apel et al.,
2010). Five animals were 85 days of age at the time of
tissue harvest (classified as the ‘‘young’’ or 3-month old
age group), three were 12-month old and one was 18month old (together forming the ‘‘aged’’ group) and six
were 30-month old (termed the ‘‘geriatric’’ group). Age
group classifications were made on the basis of longevity
studies that report 50 and 90% mortality ages of 23 and
28 months, respectively, for male Fisher 344 rats dying
of natural causes (Thurman et al., 1994), and correspond
to age-group names used in previous rat models of age
and SCI (Siegenthaler et al., 2008a). The average (SD)
mass of the animals at the time of tissue harvest was
261 (24) g for the Young group, 475 (63) g for the Aged
group, and 566 (65) for the Geriatric group. The soft tissues surrounding the vertebral column (including muscle and fascia) were removed by gross dissection. The
articulations between adjacent vertebrae were conserved
with the spinal cord inside, and the specimens were
trimmed to include only the first cervical (C1) to the second thoracic (T2) vertebrae. We used nylon fishing line
and plastic zip ties to securely mount the dorsal side of
each vertebral column along the longitudinal aspect of a
polyvinyl chloride baseplate (15 40 2 mm). Pilot
results (collected using the imaging and measurement
procedures outlined below) from a specimen mounted in
neutral and 20 extended postures demonstrated minimal influence of extension on our spine geometry measures (e.g., vertebral canal depth was within 2.0% at C3,
2.2% at C4, 0.8% at C5, 0.9% at C6, and 1.8% at C7;
CPD was within 2.3% at C2/C3, 2.2% at C3/C4, 1.4% at
C4/C5, 0.1% at C5/C6 and C6/C7, 1.9% at C7/T1). Therefore, specimens were mounted in a neutral configuration
that removed any natural curvature of the spine. Specimens were inserted into low density polyethylene sample
vials (Nalgene 18-mL sample vials with snap caps,
Fisher Scientific, Nepean, Canada) and stored in a 10%
buffered formalin solution. This study received approval
from the Animal Care Committee at the University of
British Columbia (certificate #A08-0594).
Imaging Procedures
A microCT scanner (lCT35, SCANCO Medical AG,
Switzerland) was used for imaging purposes. Each specimen was scanned in a formalin solution using an in
vitro scanning protocol (70 kVp, 114lA, and 100 ms integration time) resulting in an isotropic 30 lm voxel size.
A 30-mm section of the vertebral column was scanned
resulting in 1,000 axial (transverse plane) images (Fig.
1). The samples were scanned with the long axis of the
vertebral column aligned along the vertical axis of the
micro-CT image coordinate system. This minimized any
beam-hardening effects by minimizing the bone tissue
volume that the x-ray beam passed through. In addition,
the image reconstruction algorithm within the analysis
software (Scanco Evaluation Program v 6.0, SCANCO
Medical AG, Switzerland) provided correction for beamhardening artefact. Following scanning, the software’s
evaluation script ‘‘reformat to axial cuts’’ was used to
transform the data into sagittal plane images of the
specimen (Fig. 2).
Image Analysis
All geometric variables were measured using the
Scanco image analysis software noted above. Our specimens were always positioned in the lCT such that the
sagittal plane on axial images was horizontal (Fig. 1). To
determine the image that represented the sagittal midline, one axial slice at each of C2, C4, and C6 was evaluated. Specifically, the row of pixels that best
approximated the sagittal midline of the vertebra was
recorded for the representative C2, C4, and C6 image
slices. We averaged these three values to determine the
corresponding sagittal image slice that best approximated the midline for the overall vertebral column.
From this midsagittal image, several measurements
were made for each vertebra from C2 to T1 (Fig. 2).
First, ventral vertebral body height (VBHV; distance
from the rostral to the caudal point on the ventral
side of the vertebral body) and dorsal vertebral body
height (VBHD; distance from the rostral to the caudal
point on the dorsal side of the vertebral body) were
measured. The dorsal midpoint of the vertebral body
(calculated from VBHD) was used in measuring vertebral canal depth (VCD; distance to the lamina along a
line perpendicular to the dorsal surface of the vertebral body) and vertebral body depth (VBD; distance to
the ventral aspect of the vertebral body along a line
perpendicular to the dorsal surface of the vertebral
body). CPD was calculated as the most rostral point
on the dorsal aspect of a vertebral body to the most
caudal aspect of the lamina on the immediately rostral
vertebra. Intervertebral disc thickness (IDT) was
measured as the distance of a line, originating at the
ventral-dorsal midpoint on the rostral aspect of a vertebral body and perpendicular to the rostral surface,
to the caudal aspect of the immediately rostral
vertebral body (Fig. 2). Finally, vertebral canal area
(VCAsag) was measured by tracing the outline of the
vertebral canal from the rostral aspect of C3 to the
caudal aspect of C7.
We calculated additional geometric parameters from
the axial images (Fig. 1). The dorsal midpoint of the vertebral body (defined above) informed the selection of specific
axial images from the entire image stack. Vertebral canal
width (VCW) at levels C3 to T1 was measured as the widest transverse distance across the vertebral canal. Axial
vetebral canal area (VCAax) at levels C3 to T1, and vertebral body area (VBA) from C2 to T1, were measured by
manually tracing a line around each structure.
Image analysis was performed by a single assessor
across all specimens. To test inter-rater reliability, a second assessor independently measured each geometric
variable for 9 of the 15 specimens. Analysis software
(SPSS Version 17.0, SPSS, Chicago) was used to calculate intraclass correlation coefficients (ICC) using an
alpha, two-way random effects model evaluating for
absolute agreement. The ICC values for each variable
(e.g., vertebral canal depth) were averaged across vertebral levels. The percent differences (and ICC values)
between the measures from the two observers averaged
2.7% (0.760) for VBHV, 1.5% (0.895) for VBHD, 1.2%
(0.853) for VCD, 2.5% (0.969) for VBD, 1.2% (0.896) for
CPD, 6.6% (0.856) for IDT, 1.4% (0.959) for VCAsag, 1.4%
(0.845) for VCW, 1.9% (0.901) for VCAax, and 6.7%
(0.829) for VBA.
EFFECTS OF AGE ON SPINE MORPHOMETRY IN RATS
1329
Fig. 1. Axial microCT images of a young specimen labelled from C2 to T1. Measurement approach for
VBA, VCW, and VCAax provided in the C3, C6, and T1 images, respectively.
Clinical Assessment of Degeneration
Three orthopaedic spine surgeons independently rated
the degree of intervertebral disc degeneration in each
specimen. Each surgeon was board certified and engaged
in a Spine Fellowship run by the Vancouver Spine Program at the University of British Columbia and Vancouver General Hospital. The surgeons were initially
provided with a sample midsagittal image that illustrated the bony anatomy of the cervical spine in a
healthy rat. They were then provided with the midsagittal lCT image of each specimen. Based on Kettler and
Wilke’s (2006) review of existing grading systems and
demonstration of inter-rater reliability (Cote et al.,
1997), the surgeons used Kellgren et al.’s (1963) 5-point
scale (Table 1) to rate the overall degree of intervertebral disc degeneration (degen) on the anterior (ventral)
and posterior (dorsal) aspects of the C2 to T1 vertebral
column. The ICCs across raters were 0.741 for ventral
degen and 0.443 for dorsal degen, which correspond to
substantial and moderate inter-rater reliability, respectively (Landis and Koch, 1977). The three ratings for
each specimen and aspect (ventral or dorsal) combination were averaged to provide a single ventral and a sin-
gle dorsal numeric outcome on a continuous scale for
each specimen.
Statistical Analysis
All statistical analyses were performed with a software package using an a of 0.05 (SPSS Version 17.0,
SPSS, Chicago). We used linear mixed models using a
restricted maximum likelihood estimation approach to
test the effect of age group (young, aged, and geriatric)
and cervical level (C2, C3, etc.) on each of the multisegment dependent variables, and of age group and vertebral body aspect (ventral or dorsal) on ratings of
intervertebral disc degeneration. This analysis approach
had the advantage over a mixed model analysis of variance that specimens with missing data cells (which
occurred for one specimen at the C2 level) were not listwise excluded. The models were run with both homogeneous and heterogeneous autoregressive covariance
structures—the ones that provided the lowest Akaike’s
Information Criteria (an index of model fit in which
goodness-of-fit improves as values decrease) are
reported. A one factor (between group) analysis of
1330
LAING ET AL.
Fig. 2. Midsagittal microCT image of a young specimen from the second cervical (C2) to second thoracic (T2) vertebra. Measurement approach for ventral and dorsal vertebral body height (VBHV and VBHD)
illustrated at the C4 level, CPD at the C4/5 level, and vertebral body depth (VBD) and vertebral canal
depth (VCD) at the C6 level. Inset focusing on C5/C6 demonstrates method for measuring IDT.
TABLE 1. Kellgren et al. (1963) scale for grading intervertebral disc degeneration in the cervical spine
Grade
Criteria
0
1
2
3
4
Absence of degeneration in the disc
Minimal osteophytosis
Minimal osteophytosis; possible narrowing of the disc space; some sclerosis of vertebral plates
Moderate narrowing of the disc space; definite sclerosis of the vertebral plates; osteophytosis
Severe narrowing of the disc space; sclerosis of the vertebral plates; multiple large osteophytes
variance was used to assess the effect of age on VCAsag.
When the interaction effects were ordinal (i.e., the magnitude of the differences between age groups differed
across some vertebral levels but in all cases the rank
order of young, aged, geriatric remained constant), we
interpreted them in concert with main effects (Howell,
2002). As our primary interest was in age-related effects,
we used independent t-test pairwise comparisons (with
Bonferroni corrections) to identify significant differences
between groups when the results indicated significant
main effects for age. For cases of significant main effects
of vertebral level, we described the general trends
observed. The statistical powers associated with post hoc
tests for each variable across age groups were calculated
with the G*Power 3.1 software application (Faul et al.,
2007). Finally, to provide some insight into the influence
of animal mass vs. age [which are known to be positively
associated (Thurman et al., 1994)] on vertebral canal
1331
EFFECTS OF AGE ON SPINE MORPHOMETRY IN RATS
geometry, we used Pearson correlation analysis to assess
the association between mass and age, and between
mass and VCD, VCW, and VCAax, at the C5 level, and
CPD at the C4/C5 level. Furthermore, we performed
stepwise multiple regression analyses to determine the
additional variance (beyond age) that mass explained for
the C5 vertebral canal measures.
RESULTS
Tables 2–5 summarize the results for all variables
across age groups and vertebral levels, whereas Table 6
indicates the test statistic (F) and probability (P) values
from the statistical analyses. For geometric variables,
we observed significant main effects of age on all outcomes except IDT, in addition to significant main effects
of vertebral level. There were significant interaction
effects (age X vertebral level) for all geometric variables
except VCAax. However, as the majority of the interac-
tions were ordinal in nature we interpreted both main
and interaction effects (Howell, 2002).
In general, the magnitude of the geometric measures
increased with advancing age (Tables 2–5). Post hoc tests
(Table 6) indicated that there were significant differences
between the young and aged specimens, and young and
geriatric specimens, on all geometric variables except IDT.
Specifically, compared to the young specimens, the values
(excluding IDT) were on average 15.0% (SD ¼ 9.7%) larger
for the aged group (ranging from a 9.1% increase for VCW
to a 31.3% increase for VCAsag), and 21.5% (SD ¼ 13.4%)
larger for the geriatric specimens (ranging from an 11.4%
increase for VCW to a 37.5% increase for VCAsag). In contrast, the aged and geriatric groups were significantly different from each other for only VBD and VBA with the
geriatric specimens an average (SD) of 15.4 (10.7)% and
14.0 (7.6)% larger, respectively.
There was less consistency in the changes in geometric measures across vertebral levels. For vertebral canal
TABLE 2. Average (SD) values for canal pinch diameter (CPD) and intervertebral disc thickness (IDT)
across age groups and vertebral levels. % difference values are relative to the Young group with 1 values
representing an increase
Cervical vertebral level
CPD (mm)
Young
Aged
% difference
Geriatric
% difference
IDT (mm)a
Young
Aged
Geriatric
C2/C3
C3/C4
C4/C5
C5/C6
C6/C7
C7/T1
Avg
3.85 (0.03)
4.53 (0.09)
17.7
4.62 (0.21)
20.0
3.26 (0.11)
3.85 (0.17)
18.1
3.95 (0.12)
21.2
3.03 (0.13)
3.56 (0.15)
17.5
3.78 (0.14)
24.8
2.97 (0.05)
3.35 (0.09)
12.8
3.50 (0.14)
17.8
3.13 (0.07)
3.33 (0.08)
6.4
3.50 (0.14)
11.8
3.25 (0.07)
3.56 (0.10)
9.5
3.56 (0.11)
9.5
–
–
13.7
–
17.5
0.54 (0.07)
0.44 (0.07)
0.46 (0.05)
0.54 (0.03)
0.47 (0.03)
0.56 (0.16)
0.51 (0.08)
0.42 (0.04)
0.44 (0.06)
0.51 (0.08)
0.44 (0.06)
0.49 (0.05)
0.46 (0.07)
0.41 (0.05)
0.45 (0.03)
0.33 (0.05)
0.33 (0.04)
0.41 (0.04)
–
–
–
a
% difference not included as no significant effect of age observed.
TABLE 3. Average (SD) values for vertebral canal geometry variables across age groups and vertebral
levels. % difference values are relative to the Young group with 1 values representing an increase
Cervical vertebral level
C2
C3
VCD (mm)
Young
3.84 (0.08) 3.44 (0.03)
Aged
4.49 (0.12) 3.94 (0.14)
% difference
16.9
14.5
Geriatric
4.55 (0.30) 3.98 (0.10)
% difference
18.5
15.7
VCW (mm)
Young
–
4.25 (0.16)
Aged
–
4.43 (0.15)
% difference
–
4.2
Geriatric
–
4.52 (0.10)
% difference
–
6.4
VCAax (cm2)
Young
–
0.119 (0.005)
Aged
–
0.145 (0.010)
% difference
–
21.8
Geriatric
–
0.152 (0.006)
% difference
–
27.7
C4
C5
C6
C7
T1
Avg
3.10 (0.05)
3.50 (0.13)
12.9
3.69 (0.09)
19.0
2.99 (0.03)
3.42 (0.14)
14.4
3.65 (0.19)
22.1
2.93 (0.06)
3.29 (0.12)
12.3
3.45 (0.13)
17.7
2.90 (0.05)
3.23 (0.09)
11.4
3.27 (0.08)
12.8
2.87 (0.04)
3.17 (0.10)
10.5
3.14 (0.09)
9.4
–
–
13.3
–
16.5
4.75 (0.10)
5.00 (0.12)
5.3
5.08 (0.11)
6.9
4.74 (0.09)
5.18 (0.19)
9.3
5.26 (0.06)
11.0
5.01 (0.13)
5.48 (0.14)
9.4
5.57 (0.08)
11.2
5.06 (0.14)
5.70 (0.24)
12.6
5.80 (0.15)
14.6
5.03 (0.15)
5.62 (0.21)
11.7
5.73 (0.07)
13.9
–
–
9.1
–
11.4
0.126 (0.004) 0.126 (0.002) 0.131 (0.004) 0.130 (00.005) 0.121 (0.005)
–
0.148 (0.009) 0.152 (0.010) 0.156 (0.010) 0.156 (0.007)
0.144 (0.011)
–
17.5
20.6
19.1
20.0
19.0
19.7
0.157 (0.005) 0.162 (0.005) 0.164 (0.004) 0.161 (0.008)
0.151 (0.002)
–
24.6
28.6
25.2
23.8
24.8
25.8
VCD, vertebral canal depth; VCW, vertebral canal width; VCAax, axial vertebral canal area.
1332
LAING ET AL.
TABLE 4. Average (SD) values for vertebral body geometry variables across age groups and vertebral
levels. % difference values are relative to the Young group with 1 values representing an increase
Cervical vertebral level
C2
VBHV (mm)
Young
Aged
% difference
Geriatric
% difference
VBHD (mm)
Young
Aged
% difference
Geriatric
% difference
VBA (cm2)
Young
Aged
% difference
Geriatric
% difference
VBD (mm)
Young
Aged
% difference
Geriatric
% difference
C3
C4
C5
C6
C7
T1
Avg
3.01 (0.13)
4.04 (0.46)
34.2
4.21 (0.81)
39.9
3.04 (0.15)
3.19 (0.10)
4.9
3.04 (0.54)
0.0
2.71 (0.11)
2.97 (0.12)
9.6
2.88 (0.24)
6.3
2.52 (0.08)
2.84 (0.15)
12.7
2.94 (0.15)
16.7
2.53 (0.09)
2.83 (0.16)
11.9
2.81 (0.05)
11.1
2.57 (0.11)
2.85 (0.15)
10.9
2.86 (0.09)
11.3
2.75 (0.05)
3.20 (0.13)
16.4
3.20 (0.12)
16.4
–
–
14.4
–
14.5
2.95 (0.14)
3.48 (0.30)
18.0
3.58 (0.83)
21.4
3.06 (0.10)
3.72 (0.08)
21.6
3.76 (0.12)
22.9
2.85 (0.11)
3.27 (0.14)
14.7
3.41 (0.06)
19.6
2.65 (0.15)
3.10 (0.12)
17.0
3.17 (0.07)
19.6
2.71 (0.14)
3.16 (0.15)
16.6
3.27 (0.10)
20.7
2.65 (0.07)
3.02 (0.14)
14.0
3.06 (0.08)
15.5
2.71 (0.10)
3.24 (0.09)
19.6
3.27 (0.12)
20.7
–
–
17.3
–
20.0
0.035 (0.005) 0.033 (0.003) 0.037 (0.003) 0.035 (0.002) 0.038 (0.003) 0.038 (0.003) 0.039 (0.004)
–
0.028 (0.001) 0.036 (0.002) 0.042 (0.003) 0.043 (0.001) 0.043 (0.004) 0.050 (0.006) 0.049 (0.004)
–
20.0
9.1
13.5
22.9
13.2
31.6
25.6
13.7
0.030 (0.001) 0.042 (0.007) 0.051 (0.005) 0.043 (0.005) 0.050 (0.005) 0.059 (0.009) 0.058 (0.005)
–
14.3
27.3
37.8
22.9
31.6
55.3
48.7
29.9
1.61 (0.16)
1.28 (0.36)
20.5
1.66 (0.19)
3.1
1.46 (0.06)
1.63 (0.21)
11.6
1.95 (0.20)
33.6
1.61 (0.07)
1.97 (0.09)
22.4
2.07 (0.16)
28.6
1.58 (0.05)
1.96 (0.03)
24.1
1.93 (0.30)
22.2
1.46 (0.08)
1.78 (0.03)
21.9
2.03 (0.15)
39.0
1.40 (0.06)
1.77 (0.21)
26.4
2.19 (0.16)
56.4
1.47 (0.14)
1.88 (0.40)
27.9
2.20 (0.14)
49.7
–
–
16.3
–
33.2
VBHV, ventral vertebral body height; VBHD, dorsal vertebral body height; VBA, vertebral body area; VBD, vertebral body
depth.
TABLE 5. Average (SD) values for mid-sagittal
vertebral canal area (VCAsag; from the rostral aspect
of C3 to the caudal aspect of C7) and intervertebral
disc degeneration (degen). % difference values are
relative to the Young group with positive values
representing an increase
degen
2
Young
Aged
% Difference
Geriatric
% Difference
VCAsag (cm )
ventral
dorsal
0.48 (0.01)
0.63 (0.04)
31.3
0.66 (0.02)
37.5
1.33 (0.62)
1.33 (0.81)
0
2.61 (1.02)
96.2
0.80 (0.51)
0.67 (0.47)
16.3
1.39 (0.84)
73.8
measures (Fig. 3), CPD decreased from C2/C3 (average
(SD) ¼ 4.34 (0.38) mm) to C5/C6 (3.28 (0.26) mm) before
plateauing caudally. VCD consistently decreased from
C2 (4.28 (0.39) mm) to T1 (3.06 (0.16) mm), whereas
VCW increased from C3 (4.41 (0.17) mm) to T1 (5.47
(0.35) mm). VCAax was largest at C6 (0.151 (0.016) cm2),
decreasing to similar values at both C3 (0.139 (0.016)
cm2) and T1 (0.139 (0.015) cm2).
Regarding vertebral body measures across levels of
the vertebral column, VBHV decreased from C3 (average
(SD) ¼ 3.08 (0.34) mm) to C6 (2.72 (0.17) mm) before
increasing (to 3.05 (0.24) mm) at T1 – a similar trend
was observed for VBHD. VBD was smallest at C2 (1.53
(0.28) mm), with local peaks at C4 (1.89 (0.24) mm) and
T1 (1.87 (0.39) mm). VBA generally increased from C2
0.031 (0.004) cm2) to T1 (0.049 (0.009) cm2).
We observed significant interaction effects for all geometric variables except VCAax, most of which were ordinal
in nature (Tables 2–6; Fig. 3). Age-related differences were
greatest at the rostral segments for VCD, CPD, and VBHV.
In contrast, age-related differences tended to be more
prevalent at caudal regions for VBD, VCW, and VBA.
There was a nonsignificant trend between degen and
age (P ¼ 0.069; Tables 5 and 6), with a tendency toward
greater radiographic evidence of degeneration in the
geriatric specimens [average (SD) ¼ 2.00 (1.10)] compared to the young [1.07 (0.60)] and aged [1.00 (0.71)]
groups. Degen was significantly more pronounced (P <
0.001) on the ventral [1.84 (1.02)] compared to dorsal
[1.00 (0.70)] aspect of the vertebral bodies. No significant
interaction effects were observed (P ¼ 0.171).
The statistical power (Table 6) of our analyses was
lowest when assessing potential differences across the
aged and geriatric groups. Averaging across vertebral
levels or dorsal/ventral aspects, the mean probability of
correctly rejecting the null hypothesis (i.e., no difference
across age groups) was above 80% for seven of the
eleven dependent variables for the young versus aged
comparisons, and eight of the eleven variables for the
young versus geriatric comparisons. In contrast, the
highest power reached for the aged versus geriatric comparisons was 0.509.
Animal age was significantly and positively associated
with mass (r ¼ 0.905, P < 0.001). The results of overall
analyses (including all specimens) demonstrated that
mass was significantly associated with C4/C5 CPD (P <
0.001), C5 VCD (P < 0.001), C5 VCW (P < 0.001), and
1333
EFFECTS OF AGE ON SPINE MORPHOMETRY IN RATS
TABLE 6. Summary across all dependent variables of test statistic (F) and probability (P) values
associated with main and interaction effects, and probability (P) and powerb values for posthoc tests
comparing across age groups
P
CPD
IDT
VBHV
VBHD
VCD
VCW
VBA
VBD
VCAax
VCAsag
degen
Pairwise comparisons (P)a
F
Power
Age
Vert
level
Age X
level
Age
Vert
level
Age X
level
Youngaged
Younggeriatric
Agedgeriatric
Youngaged
Younggeriatric
Agedgeriatric
<0.001
0.09
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
0.069
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
N/A
<0.001
0.01
0.038
0.03
0.012
0.006
0.005
0.002
<0.001
0.752
N/A
0.171
88
2.8
14.2
27.8
72.9
41.8
26.7
23.4
59.4
57.3
3.4
151.6
15.7
27.4
66.8
82.2
148.1
15.9
10.9
22.4
N/A
26.7
3.9
2.4
2.4
2.8
3.1
2.9
3.9
4.5
0.7
N/A
2.1
<0.001
0.117
0.002
<0.001
<0.001
<0.001
0.009
0.028
<0.001
<0.001
1
<0.001
1.000
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
0.149
0.07
0.226
1.000
0.928
0.187
0.505
0.020
0.016
0.105
0.373
0.145
0.984
0.353
0.827
0.978
1.000
0.873
0.755
0.765
0.996
1.000
0.057
1.000
0.293
0.751
0.922
1.000
0.983
0.881
0.830
1.000
1.000
0.421
0.286
0.273
0.079
0.191
0.267
0.184
0.509
0.504
0.443
0.255
0.369
CPD, canal pinch diameter; IDT, Intervertebral disc thickness; VBHV, ventral vertebral body height; VBHD, dorsal vertebral body height; VCD, vertebral canal depth; VCW, vertebral canal width; VBA, vertebral body area; VBD, vertebral body
depth; VCAax, axial vertebral canal area, VCAsag, mid-sagittal vertebral canal area; degen, intervertebral disc
degeneration.
a
Bonferonni adjustments incorporated.
b
Power calculated with Gpower 3.1 (Faul et al., 2007) using a t-test family, ’Means: difference between two independent
means’ option, two tailed test, and a ¼ 0.05. The mean value across vertebral levels or ventral-dorsal aspects is presented.
TABLE 7. Pearson correlation coefficients (r)
and significance (p) values for correlation analyses
assessing the relationship between animal mass and
vertebral canal geometry measures at the fifth
cervical vertebrae (C5)
Specimens
Young
Aged
Geriatric
All ages
r
p
r
p
r
p
r
p
CPD @
C4/C5
VCD @
C5
VCW @
C5
VCAax
@ C5
0.536
0.351
0.075
0.925
0.088
0.869
0.868
<0.001
0.654
0.232
0.396
0.604
0.289
0.578
0.81
<0.001
0.719
0.171
0.256
0.744
0.076
0.887
0.881
<0.001
0.557
0.329
0.809
0.191
0.323
0.532
0.731
0.002
CPD, canal pinch diameter; VCD, vertebral canal depth;
VCW, vertebral canal width; VCAax, axial vertebral canal
area.
mal mass provided no substantial improvements over
age in the percentage of variance explained in our spinal
canal geometry measures. Specifically, when mass was
added as a predictive factor to the reference model that
included animal age, the adjusted r2 values decreased
slightly for C4/C5 CPD (r2 ¼ 0.809 vs. r2 ¼ 0.817) and
C5 VCD (r2 ¼ 0.785 vs. r2 ¼ 0.799) and increased
slightly for C5 VCW (r2 ¼ 0.757 vs. r2 ¼ 0.717) and C5
VBAax (r2 ¼ 0.836 vs. r2 ¼ 0.827).
Fig. 3. Average (SD) values of: A: CPD; B: vertebral canal depth
(VCD); and C: VCW across age groups and vertebral levels.
C5 VCAax (P ¼ 0.002) (Table 7). However, there were no
significant associations between mass and these variables when evaluating each age cohort separately (Table
7). In addition, regression analyses indicated that ani-
DISCUSSION
The goal of this study was to perform a detailed characterization of the morphology and degenerative state
of the cervical spine in Fisher 344 rats, and to determine the influence of age on these variables. These
data are essential for interpreting the results of animal
models of SCI that assess the influence of age on tissue
damage severity. Regarding our first aim, we observed
1334
LAING ET AL.
that 9 of 10 geometric variables measured from the cervical spinal columns of Fisher 344 rats were significantly larger for the 12–18-month old (by 15.0% on
average) and 30-month old (by 21.5% on average) specimens compared to young adult (3 months) specimens.
However, significant age-related increases were generally not observed between rats in the aged (12–18
months) and geriatric (30 months) groups. Related to
our second aim, radiographic signs of intervertebral
disc degeneration were more evident on the ventral
compared to the dorsal aspect, with a nonsignificant
trend of more advanced degeneration in the geriatric
specimens.
In addition to our novel findings of age-related
changes, the cervical canal dimensions from our young
specimens correspond to previous results from rats. Our
values from Fisher 344 rats are similar to those measured by Flynn & Bolton from Sprague-Dawley rats
(2007) with vertebral canal depth being largest at C2
and progressively decreasing caudally to T1 [by 25.2% in
this study and 28.5% in Flynn and Bolton (2007)]. Our
VCW values are also similar, increasing 17% caudally
from C3 to C7. Our results do not correspond as well to
those measured from sheep (Wilke et al., 1997) in which
vertebral canal depth has been reported to increase (by
17%) from C3 to C7. It is unclear whether these relate
to functional differences between species, or are the
result of different measurement protocols [microCT in
the current study vs. a handheld micrometer in Wilke
et al. (1997)].
The intervertebral disc degeneration findings have important implications for rat models of aging and SCI.
Intervertebral disc degeneration is common, occurring in
up to 50% of humans above the age of 40 years of age,
and in 85% of persons over the age of 60 (Lehto et al.,
1994; Matsumoto et al., 1998). It also has implications
for SCI, with cervical disc generation often associated
with anterior compression of the spinal cord, and with
accelerated progression in elderly persons (Okada et al.,
2009). Slight to moderate disc degeneration can result in
intervertebral instability (Dai, 1998; Miyazaki et al.,
2008), which may potentially increase the risk of vertebral dislocations and neurological injuries associated
with spinal cord shearing. In contrast, severe intervertebral disc degeneration is associated with increased intervertebral stability (Dai, 1998; Miyazaki et al., 2008) in
part the result of osteophytosis at the discovertebral
junction. Although they may assist in stabilizing the
joint, osteophytic materials on posterior discovertebral
junctions can result in cervical spondylosis and local
pressure points that contribute to an increased risk of
spinal cord compression injuries (Shedid and Benzel,
2007). In this study, based on radiographic signs we
observed no change in the degenerative state of the discs
between young and aged specimens, and only a trend toward increased degeneration in the geriatric group. This
corresponds to Zhang et al. (2009) who, through histological analysis of midsagittal tissue sections, observed no
differences in intervertebral disc degenerative in the
lumbar spine between 6- and 22-month old SpragueDawley rats. Less expected was our observation that evidence of degeneration was significantly greater on the
ventral aspect of the discs and vertebral bodies compared with the dorsal aspect. Few osteophytes were
observed within the vertebral canal. Consequently, while
intervertebral disc degeneration in a rat model may alter the mechanical properties of the cervical spinal column (e.g., stability, stiffness), the lack of bone spurs and
discontinuities within the vertebral canal suggest little
risk of age-related differences in local pressure points on
the spinal cord during transverse or shear loading.
Similar to previous findings (Thurman et al. 1994), we
observed a significant association between increasing
animal age and body mass. However, animal mass provided minimal improvements over animal age in predicting vertebral canal geometry at the fifth cervical
vertebrae. Furthermore, animal mass was not predictive
of our vertebral canal measures when individual age
cohorts were evaluated separately (Table 7). These
results could suggest that age-related increases in mass
may be more related to changes in skeletal geometry,
whereas variability in mass at a given age may be indicative of differences in adiposity. However, the small sample size in these subset analyses is a major limitation.
Consequently, additional studies are required to provide
a more detailed characterization of the influence of mass
on vertebral column morphometry in rodent models of
SCI.
Our results generally correspond to the trends in vertebral canal dimensions across levels of the cervical
spine measured from humans. Similar to humans, vertebral canal depth in our specimens was largest at C2 and
progressively decreased caudally to T1 (Panjabi et al.,
1991; Tatarek, 2005). We observed VCW to progressively
increase caudally from C2 before plateauing in the C7 to
T1 region. This corresponds to increases in human values from C3 to C6, but does not reflect the decreases
reported between C2-C3, and C6-C7 (Panjabi et al.,
1991; Tatarek, 2005). Our trends for VCAax are similar
to that of Panjabi et al. (1991), with values decreasing
from C2 to C3, then increasing to C6 and C7, before
decreasing again at C7 or T1. However, unlike common
observances in older humans (Okada et al., 2009), we
observed no evidence of cervical spinal stenosis or cervical myelopathy in our aged or geriatric rats. This difference could be a result of the relatively small sample in
our geriatric group as, similar to humans, they may only
afflict a small proportion of the population. Alternatively,
such between-species differences may in fact exist as a
result of differential loading patterns on the cervical spinal column between bipedal and quadripedal mammals
(e.g., greater shear forces in the latter). Further studies
are required to investigate such questions from both evolutionary and biomechanical perspectives.
These data have implications for studies that use rat
models to assess age-related changes in the distribution
and severity of spinal cord injuries. First, there were no
differences between the aged and geriatric groups for
nine of our eleven dependent variables. This suggests
that, from a morphological perspective, 12–18-month old
rats have similar spinal geometric characteristics compared to rats twice their age, and could be considered for
use in spinal column aging studies. Second, these data
indicate that there are differences on the order of 15%
between geometric measures of young and aged Fisher
344 male rats. Consequently, to produce similar mechanical loads to the spinal cord of young and aged rats during induced SCI, different injury system parameters
may need to be employed. For example, as the vertebral
canal depth was 13.3% (on average) larger in aged rats,
EFFECTS OF AGE ON SPINE MORPHOMETRY IN RATS
using a similar contusion depth across age groups may
result in less mechanical strain of the spinal cord (and
less severe tissue damage) in the aged specimens. These
are important issues to be considered when developing
experimental protocols for studies assessing the influence of aging on SCI—further studies are required to
provide additional insight in this area.
Vertebral fracture-dislocation has been cited as the
most common mechanism of cervical SCI in humans
(Sekhon and Fehlings, 2001), is associated with ‘‘complete’’ SCI in humans (Pickett et al., 2006), and in rats
causes more severe histological indices of damage compared to contusion and flexion-distraction injury mechanisms (Choo et al., 2007; 2008; 2009). Despite this,
fracture-dislocation is relatively understudied injury
mechanism in experimental SCI research. The geometric
variable most relevant to AP cervical dislocation is CPD,
and changes in this variable have been assessed during
simulated frontal and rear impacts (Ito et al., 2004;
Ivancic et al., 2006). Using 3-month old Sprague-Dawley
rats, Choo et al. (2009) classified a 2.6-mm dislocation as
moderate-to-severe with a mortality rate of 10%. The
current results from Fisher 344 rats indicate that a 2.6mm C4/C5 dislocation would be 85.8% of CPD for 3month olds (the age most commonly used for experimental SCI studies), but only 73.0% and 68.8% of CPD for
12–18- and 30-month olds, respectively. This further
indicates the potential need to account for age-related
changes in spine geometry in studies that investigate
whether advanced age influences SCI outcomes following
fracture-dislocation injury mechanisms. The imaging
and analysis procedures used in this study demonstrated
high inter-rater reliability with measurements across
raters averaging within 1.2% for both vertebral canal
depth (ICC ¼ 0.853) and CPD (ICC ¼ 0.896). Therefore,
this experimental approach appears sufficiently accurate
to assist in the development of age-specific/equivalent
models of cervical SCI in rats.
There were several limitations associated with this
study. First, we only included male specimens in our
study. However, we feel justified in this as Flynn and
Bolton (2007) reported no sex-related differences in cervical VCW or depth in Sprague-Dawley rats (even
though the males’ masses were on average 31% larger).
Second, despite our best efforts, we were unable to
remove all of the vertebral column extension in our
specimens. The importance of this issue is highlighted
by findings that spine flexion/extension induced by
dynamic front and rear impacts can result in a narrowing of CPD in the cervical spine (Ito et al., 2004; Ivancic
et al., 2006). However, we feel this will have a limited
influence on our findings as we used a standard mounting technique across all specimens, and pilot results
from a single specimen (see ‘‘Tissue specimens’’ section)
indicated that vertebral column extension during our
static fixation had minimal influence on our microCT geometry measures. Third, using the current protocol, we
were unable to measure the geometry of the spinal cord
relative to the vertebral canal. Determination of whether
spinal cord morphometry scales with vertebral canal
dimensions will form an important research question toward the development of consistent SCI models across
age groups. Finally, our study only assessed the degree
of intervertebral disc degeneration based on radiographic images. Although we feel justified in our conclu-
1335
sions based on evidence of significant associations
between radiographic and histological indices of disc
degeneration (Benneker et al., 2005) and the demonstrated reliability of the modified Kellgren scale (Cote
et al., 1997), histological examination of the discs would
provide additional insights into potential age-related
changes in these structures (Zhang et al., 2009).
This study investigated the influence of advanced age
on cervical spine morphometry in Fisher 344 rats. It provides the first reported measures of CPD, VCA, VBA,
and intervertebral disc degeneration for this animal
model, and confirms previous findings related to vertebral canal depth and width (Flynn and Bolton, 2007).
The results indicate that spinal column measures are
15% larger in 12–18-month old compared with 3-month
old rats, with few additional changes observed in 30month old specimens. These data provide important information for the development of valid animal models of
aging and SCI.
ACKNOWLEDGEMENTS
The authors would like to thank Dr. Peter J. Apel for
providing the aged and geriatric tissue samples used in
this study. The authors would also like to acknowledge
the contributions of the orthopaedic surgeons (Dr. Stephen Kingwell, Dr. Christian Dipaola, Dr. Brian Lenehan) who performed the assessments of intervertebral
disc degeneration.
LITERATURE CITED
Apel PJ, Alton T, Northam C, Ma J, Callahan M, Sonntag WE, Li
Z. 2009. How age impairs the response of the neuromuscular
junction to nerve transection and repair: an experimental study
in rats. J Orthop Res 27:385–393.
Apel PJ, Ma J, Callahan M, Northam CN, Alton TB, Sonntag WE,
Li Z. 2010. Effect of locally delivered IGF-1 on nerve regeneration
during aging: an experimental study in rats. Muscle Nerve
41:335–341.
Benneker LM, Heini PF, Anderson SE, Alini M, Ito K. 2005. Correlation of radiographic and MRI parameters to morphological and
biochemical assessment of intervertebral disc degeneration. Eur
Spine J 14:27–35.
Chaovipoch P, Jelks KA, Gerhold LM, West EJ, Chongthammakun
S, Floyd CL. 2006. 17beta-estradiol is protective in spinal cord
injury in post- and pre-menopausal rats. J Neurotrauma 23:830–
852.
Choo AM, Liu J, Dvorak M, Tetzlaff W, Oxland TR. 2008. Secondary
pathology following contusion, dislocation, and distraction spinal
cord injuries. Exp Neurol 212:490–506.
Choo AM, Liu J, Lam CK, Dvorak M, Tetzlaff W, Oxland TR. 2007.
Contusion, dislocation, and distraction: primary hemorrhage and
membrane permeability in distinct mechanisms of spinal cord
injury. J Neurosurg Spine 6:255–266.
Choo AM, Liu J, Liu Z, Dvorak M, Tetzlaff W, Oxland TR. 2009.
Modeling spinal cord contusion, dislocation, and distraction: characterization of vertebral clamps, injury severities, and node of
Ranvier deformations. J Neurosci Methods 181:6–17.
Cote P, Cassidy JD, Yong-Hing K, Sibley J, Loewy J. 1997. Apophysial joint degeneration, disc degeneration, and sagittal curve of
the cervical spine. Can they be measured reliably on radiographs?
Spine (Phila Pa 1976) 22:859–864.
Dai L. 1998. Disc degeneration and cervical instability. Correlation
of magnetic resonance imaging with radiography. Spine (Phila Pa
1976) 23:1734–1738.
Faul F, Erdfelder E, Lang AG, Buchner A. 2007. G*Power 3: a
flexible statistical power analysis program for the social,
1336
LAING ET AL.
behavioral, and biomedical sciences. Behav Res Methods 39:
175–191.
Flynn JR, Bolton PS. 2007. Measurement of the vertebral canal
dimensions of the neck of the rat with a comparison to the
human. Anat Rec (Hoboken) 290:893–899.
Genovese T, Mazzon E, Di Paola R, Crisafulli C, Muia C, Bramanti P, Cuzzocrea S. 2006. Increased oxidative-related mechanisms in the spinal cord injury in old rats. Neurosci Lett 393:
141–146.
Gwak YS, Hains BC, Johnson KM, Hulsebosch CE. 2004. Effect of
age at time of spinal cord injury on behavioral outcomes in rat. J
Neurotrauma 21:983–993.
Howell DC. 2002. Statistical methods for psychology. 5th ed. CA:
Duxbury, Pacific Grove, ISBN 053437770X.
Ito S, Panjabi MM, Ivancic PC, Pearson AM. 2004. Spinal canal
narrowing during simulated whiplash. Spine (Phila Pa 1976)
29:1330–1339.
Ivancic PC, Panjabi MM, Tominaga Y, Pearson AM, Elena Gimenez
S, Maak TG. 2006. Spinal canal narrowing during simulated frontal impact. Eur Spine J 15:891–901.
Kannus P, Niemi S, Palvanen M, Parkkari J. 2000. Continuously
increasing number and incidence of fall-induced, fracture-associated, spinal cord injuries in elderly persons. Arch Intern Med
160:2145–2149.
Kannus P, Palvanen M, Niemi S, Parkkari J. 2007. Alarming rise in
the number and incidence of fall-induced cervical spine injuries
among older adults. J Gerontol A Biol Sci Med Sci 62:180–183.
Kellgren J, Jeffrey M, Ball J. 1963. Atlas of stand radiographs. Vol.
II. The epidemilogy of chronic rheumatism. Oxford: Blackwell Scientific. p 14–19.
Kettler A, Wilke HJ. 2006. Review of existing grading systems for
cervical or lumbar disc and facet joint degeneration. Eur Spine J
15:705–718.
Krassioukov AV, Furlan JC, Fehlings MG. 2003. Medical co-morbidities, secondary complications, and mortality in elderly with acute
spinal cord injury. J Neurotrauma 20:391–399.
Landis JR, Koch GG. 1977. The measurement of observer agreement for categorical data. Biometrics 33:159–174.
Lehto IJ, Tertti MO, Komu ME, Paajanen HE, Tuominen J, Kormano MJ. 1994. Age-related MRI changes at 0.1 T in cervical
discs in asymptomatic subjects. Neuroradiology 36:49–53.
Matsumoto M, Fujimura Y, Suzuki N, Nishi Y, Nakamura M, Yabe
Y, Shiga H. 1998. MRI of cervical intervertebral discs in asymptomatic subjects. J Bone Joint Surg Br 80:19–24.
Miyazaki M, Hong SW, Yoon SH, Zou J, Tow B, Alanay A, Abitbol
JJ, Wang JC. 2008. Kinematic analysis of the relationship
between the grade of disc degeneration and motion unit of the
cervical spine. Spine (Phila Pa 1976) 33:187–193.
Nobunaga AI, Go BK, Karunas RB. 1999. Recent demographic and
injury trends in people served by the Model Spinal Cord Injury
Care Systems. Arch Phys Med Rehabil 80:1372–1382.
NSCISC. 2010. National spinal cord injury statistical center: facts
and figures at a glance. Available at www.nscisc.uab.edu.
(accessed online on July 6, 2010).
O’Connor PJ. 2006. Trends in spinal cord injury. Accid Anal Prev
38:71–77.
Okada E, Matsumoto M, Ichihara D, Chiba K, Toyama Y, Fujiwara
H, Momoshima S, Nishiwaki Y, Hashimoto T, Ogawa J, Watanabe
M, Takahata T. 2009. Aging of the cervical spine in healthy volunteers: a 10-year longitudinal magnetic resonance imaging study.
Spine (Phila Pa 1976) 34:706–712.
Panjabi MM, Duranceau J, Goel V, Oxland T, Takata K. 1991. Cervical human vertebrae. Quantitative three-dimensional anatomy of
the middle and lower regions. Spine (Phila Pa 1976) 16:861–869.
Pickett GE, Campos-Benitez M, Keller JL, Duggal N. 2006. Epidemiology of traumatic spinal cord injury in Canada. Spine 31:799–805.
Pickett W, Simpson K, Walker J, Brison RJ. 2003. Traumatic spinal
cord injury in Ontario, Canada. J Trauma 55:1070–1076.
Priebe MM, Chiodo AE, Scelza WM, Kirshblum SC, Wuermser LA,
Ho CH. 2007. Spinal cord injury medicine. 6. Economic and societal issues in spinal cord injury. Arch Phys Med Rehabil 88:S84–
S88.
Scheff SW, Rabchevsky AG, Fugaccia I, Main JA, Lumpp JE, Jr.
2003. Experimental modeling of spinal cord injury: characterization of a force-defined injury device. J Neurotrauma 20:179–193.
Sekhon LH, Fehlings MG. 2001. Epidemiology, demographics, and
pathophysiology of acute spinal cord injury. Spine 26:S2–12.
Shedid D, Benzel EC. 2007. Cervical spondylosis anatomy: pathophysiology and biomechanics. Neurosurgery 60:S7–S13.
Siegenthaler MM, Ammon DL, Keirstead HS. 2008a. Myelin pathogenesis and functional deficits following SCI are age-associated.
Exp Neurol 213:363–371.
Siegenthaler MM, Berchtold NC, Cotman CW, Keirstead HS. 2008b.
Voluntary running attenuates age-related deficits following SCI.
Exp Neurol 210:207–216.
Tatarek NE. 2005. Variation in the human cervical neural canal.
Spine J 5:623–631.
Thurman JD, Bucci TJ, Hart RW, Turturro A. 1994. Survival, body
weight, and spontaneous neoplasms in ad Libitum-fed and foodrestricted Fischer-344 rats. Toxicol Pathol 22:1–9.
Wilke HJ, Kettler A, Wenger KH, Claes LE. 1997. Anatomy of the
sheep spine and its comparison to the human spine. Anat Rec
247:542–555.
Zhang YG, Sun ZM, Liu JT, Wang SJ, Ren FL, Guo X. 2009. Features of intervertebral disc degeneration in rat’s aging process. J
Zhejiang Univ Sci B 10:522–527.
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spina, effect, morphometric, advanced, mode, degeneration, state, rat, age, cervical
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