The prevalence of narrowing of the dorsal nerve root
foramen.
Abstract
The equine thoracolumbar spine is an area where several types of osseous pathologies are
found. It is still a challenging job to find the exact location of the pain and the possible
underlying pathologies. Focusing on the intervertebral foramina and its osteophyt forming,
which could interfere with the dorsal nerve branches. Can the closure of the dorsal nerve
root foramen be correlated with back pain?
Twenty horses (mean ±SD age: 13.8±8.6; 10 geldings, 10 mares) were presented to the clinic
for euthanasia. They were scored on back pain through a standard protocol. After
euthanasia the spine from Th16 – S4 ware obtained and prepared for scoring the grade of
the intervertebral foramina. The correlation with back pain when more than 30% of the
spine was affected (grade 3 or 4) was calculated using logistic regression.
There is a greater chance (3.33 times higher) for horses with both thoracic and lumbar
affected vertebrae to get back pain. Due to the small group of horses no significance was
displayed.
It would be interesting to see if specific pathology in the spine is correlated with age and if,
as in humans, the musculus multifidus undergoes atrophy if the patient has back pain.
Introduction
The equine thoracolumbar spine is known to be an area where several types of osseous
pathologies are found.2,3,6 Back pain clinically detected in a horse, is often difficult to localize.
Finding the precise anatomical site and the type of lesion is difficult due to the relative
inaccessibility of the vertebrae for diagnostic imaging. Therefore, the subject of back pain in
the horse is an area where much research is still needed to clarify the clinical signs, the
underlying pathologies and the appropriateness of different diagnostic techniques. As
Jeffcott stated in the early nineties4,5 the diagnosis of back pain in horses is a long and
difficult process. It involves exclusion of other diagnoses with a systematic protocol at rest,
during exercise and after exercise. Furthermore, correct understanding of the anatomy of
the horse and of the function of the spine is very important.7
After the discovery of different pathologies in the thoracolumbar area, therapy methods and
diagnostic tools have evolved. Already in the early eighties Jeffcott stated that back
pathologies can occur.3 Also in de late nineties Haussler noted many changes in the
thoracolumbar spine of Thoroughbreds,6 and states in a review that there is limited
knowledge of the functions, problems and sources of pain in the spine and pelvis of horses.8
During this research we tried to reveal the possible bony changes in the lumbar area of the
horse. We mainly concentrated on the lumbar area because that is the place where the
highest range of motion takes place.1 A literature research revealed one article2 with
information about the lateral foramina in the equine thoracolumbar vertebral column. This
article briefly describes different degrees of the lateral foramen based on a classification
scale developed for the bovine lateral foramina. Jeffcott states that the intervertebral
foramina vary in size and commonly show local osteophytes that cause narrowing of the
foramen.7 This is not known to cause local damage to the spinal nerves or to give rise to any
associated clinical signs.7
The question addressed in this study is whether there is a correlation between clinical back
problems (back muscle pain) and the pathologic findings at necropsy examination of the
formation of lateral foramina, with special reference to the possibility of neuritis.
Materials and Methods
In this study we used 20 horses (mean ±SD age: 13.8±8.6; 10 geldings, 10 mares) that had
been presented for euthanasia for reasons other than primary back pain (old age, lameness,
reproductive problems). The breeds represented were Thoroughbreds (55%), Quarter horses
(25%) and others (20 %), which included Warm blood, Morgan, Tennessee Walking horse
and Morgan x Belgian. Three horses were euthanized immediately and not evaluated
clinically. The other 17 horses were evaluated using a standard protocol (appendix 1) to
determine the presence and grade of lameness and whether back pain was present.
After euthanasia, the horse’s spine and pelvis were removed from T16 to S4. The
musculature was dissected away and the intervertebral joints were disarticulated. The
vertebrae and the pelvis were processed in a boiler for 12 hours and in a chemical solution
for 2 days. After the processing, the bones were used to grade the appearance of the
intervertebral foramina at each intervertebral level from T16/T17 to L6/S1 using the method
of Gloobe:2
0 = no changes
1 = dorsal and ventral spurs projecting into the caudal vertebral notch
2 = dorsal and ventral spurs almost touching
3 = dorsal and ventral spurs fused dividing the foramen laterally
4 = lateral foramen further divided into dorsal and ventral parts.
If a location was graded as a 3 or 4 this could indicate interference with the spinal segmental
nerve. This means that the vertebrae with a grade 3 or 4 were marked as severe and we
would like to find out if these could be correlated with back pain. For each spine the
percentage of severe lesions were calculated. If a spine had 30% or more of its spine with
vertebrae with a grade 3 or 4 this was said to be affected. Also these horses were, before
euthanasia, scored for back pain, yes or no.
The correlation was tested using a logistic regression model with the odds ratio and a
confidence interval to state the significance.
Background lumbar nerves
The nerves leaving the vertebral column trough the intertransverse foramen divide into a
dorsal and ventral branch.11,12,13 The dorsal branches are of interest because they, described
in humans, innervate the facet joints.12 Within the transverse ligaments12 at the level of the
transverse process13 the dorsal branch divides into medial and lateral branches. The medial
branch stays close to bone and divides again before exiting the intertransverse space. One
branch runs caudodorsally across the lamina of the vertebrae, around the facet joint and
continues in the groove between the articular process and the spinous process. The other
branch goes to the caudal vertebrae and its facet joint (see figure 1).13 In humans they have
described that the medial nerves also run into the multifidus muscle.12
There is an article that describes referred pain in the lower back. They state that inguinal
and/or anterior thigh pain with lower lumbar facet joint lesions may be explained as referred
pain.14
Figure 1. Anatomical overview dorsal root and dorsal vertebral medial branch.
Results
From the 17 horses that were evaluated clinically, 8 had signs of back pain and 9 had no
signs of back pain.
The majority of the horses the foraminal changes (14/20) involved the thoracic region. If we
take 30% of the spine affected (a grade 3 or 4) as severe. Than two horses had fewer than
30% of affected vertebrae and only four horses had affected lumbar vertebrae with a
percentage higher than 30%. In the total affected spine, four horses had less than 30% of the
vertebrae affected. (see table 1)
Tabel 1. Percentage of affected vertebrae with grade 3 or 4, for each horse. Including the
back pain grade.
Horse
Affected
Th (%)
Affected
L (%)
1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
0
0
25
0
0
0
50
33
0
86
14
50
38
71
43
100
67
75
75
33
0
0
0
0
0
0
0
0
0
0
0
0
0
33
0
50
0
33
0
50
(+ = back pain)
Affected
Total
(%)
0
0
14
0
0
0
40
14
0
55
10
33
28
60
30
83
40
64
50
40
Back
pain
+
+
+
+
+
+
+
+
Tabel 2. Grade of lesions per vertebrae.
Spinal level
Lesion Grade
0
1
2
3
4
TOTAL
T16-T17
Left
Right
2/19
3/19
9/19
6/19
2/19
1/19
6/19
9/19
0/19
0/19
19/19
19/19
T17-T18
Left
Right
10/19
10/19
1/19
1/19
2/19
5/19
5/19
3/19
1/19
0/19
19/19
19/19
T18-L1
Left
Right
16/20
13/20
3/20
5/20
0/20
1/20
0/20
0/20
1/20
1/20
20/20
20/20
L1-L2
Left
Right
18/20
13/18
2/20
4/18
0/20
1/18
0/20
0/18
0/20
0/18
20/20
18/18
L2-L3
Left
Right
19/20
13/18
1/20
5/18
0/20
0/18
0/20
0/18
0/20
0/18
20/20
18/18
L3-L4
Left
Right
14/19
11/17
2/19
3/17
0/19
1/17
2/19
1/17
1/19
1/17
19/19
17/17
L4-L5
Left
Right
4/9
3/9
1/9
2/9
3/9
2/9
0/9
0/9
1/9
2/9
9/9
9/9
L5-L6
Left
Right
1/1
0/1
0/1
0/1
0/1
1/1
TOTAL
Left
Right
83/126
67/121
19/126
26/121
7/126
11/121
13/126
13/121
4/126
4/121
126/126
121/121
Can narrowing of the foramen be correlated with back pain?
This was tested using logistic regression with the odds ratio and confidence interval to state
the significance. Just lumbar vertebrae or just thoracic vertebrae being affected doesn’t
seem to contribute to the occurrence of back pain. So the focus was on the total spine being
more than 30% affected, does this contribute to the occurrence of back pain?
When calculating the odds with affected both thoracic and lumbar (affect(LT(2))) you do get
a higher OR (EXP(B)=3.33) compared with affectLT=0 (see table 3). There is no significance:
wide confidence interval (0.2 – 54.5). When only one location is affected (affectLT=1) this
doesn’t give a higher risk for a horse getting back pain (Exp(B)=OR=1).
Table 3. Logistic regression model
B
Step 1a
Step 2a
AffectLT
AffectLT(1)
AffectLT(2)
Constant
Constant
S.E.
0.000
1.204
-0.693
-0.188
1.500
1.426
1.225
0.486
Wald
1.403
0.000
0.713
0.320
0.059
df
Sig.
2
1
1
1
1
Exp(B)
0.496
1.000
0.398
0.571
0.808
1.000
3.333
0.500
0.889
95.0% C.I. for
EXP(B)
Lower
Upper
0.053
0.204
a = Variable(s) entered on step 1: affectLT.
Conclusion
The odds or risk of a horse getting back pain is 3.33 times higher when both thoracic and
lumbar vertebrae have spur forming in the intervertebral foraminae compared with horses
in which there are only thoracic or lumbar lesions. This being not significant because of the
relative small group of horses, but it could be biologically/clinically important. It does give a
direction.
Discussion
The horses used covered a great age range. It would be interesting to see if back pain is age
related and if the thoracolumbar lesions are age related. The horses had been used for
different goals, but all of them weren’t in training. The degree of back pain could have
differed if they were in training.
In human literature there is evidence that lower back pain is correlated with atrophy of the
multifidus muscle. It would be interesting to correlate the pathologic findings in these horses
with the size of the multifidus muscle at the different facet joint levels.
In the human medical literature there is documentation of neurogenic and or referred pain.
Also with back pain, musculoskeletal pain, increased muscle tone and stiffness are symptoms
often seen. Still relationships between found lesions/pathology and pain are not clear. Also
there is an individual reaction/pain threshold to be taken in mind.6,15,16
The last years there has become a greater awareness of the roll the central nervous system
plays in the control of the muscle system. The central nervous system must function well to
make sure the muscles perform as desired, for coordination and levels of activity to control
external and internal forces and to withstand disturbances in the movement, function and
coordination.17,18
18.915
54.532
Literature
1. Townsend HG, Leach DH, Fretz PB. Kinematics of the equine thoracolumbar spine.
Equine Vet J. 1983, 15 (2), 117-22.
2. Gloobe H. Lateral foramina in the equine thoracolumbar vertebral column: An
anatomical study. Equine Vet J. 1984, 16 (5), 469-470.
3. Jeffcott LB. Disorders of the thoracolumbar spine of the horse – a survey of 443 cases.
Equine Vet J. 1980, 12 (4), 197-210.
4. Jeffcott LB. Rückenprobleme des Athleten “Pferd” 1. Ein Bericht über das Erkennen
und die Möglichkeiten der Diagnose. Pferdeheilkunde 9, 1993, 3, 143-150.
5. Jeffcott LB. Rückenprobleme beim Athleten Pferd 2. Mögliche Differentialdiagnosen
und Therapiemethoden. Pferdeheilkunde 9, 1993, 4, 223-236.
6. Haussler K, et all. Pathologic changes in the lumbosacral vertebrae and pelvis in
Thoroughbred racehorses. AJVR, 1999, 60 (2), 143-153.
7. Jeffcott LB, Dalin G. Natural rigidity of the horse’s backbone. Equine Vet J. 1980, 12
(3), 101-108.
8. Haussler K. The lower back and pelvis of performance horses receive a closer look.
Journal of Equine Veterinary Science, 1996, 16 (7), 279-281
9. Clayton et al. Dynamic Mobilization Exercises Increase Cross Sectional Area of
Multifidus. Equine Vet J. 2011, 43 (5), 522-9.
10. Kalichman et al. Changes in paraspinal muscles and their association with low back
pain and spinal degeneration: CT study. Eur Spine J 2010, 19, 1136–1144.
11. Sisson and Grossman’s. The anatomy of the domestic animals, volume 1, pg 633 +
677-679
12. N. Bogduk, M.D. Long, D.M. Long. The anatomy of the so-called "articular nerves" and
their relationship to facet denervation in the treatment of low-back. J Neurosurg.
1979, 51 (2), 172-7.
13. J.M. van de Weerd, F. Desbrosse, P. Clegg. Innervation and nerve injections of the
lumbar spine of the horse: a cadaveric study. Equine Vet J. 2007, 39 (1), 59-63.
14. K.M.D. Suseki, Y.M.D. Takahashi, K.M.D. Takahashi. Innervation of the Lumbar Facet
Joints: Origins and Functions. Spine, 22(5), 1997, 477-485.
15. Meehan, L., Dyson, S. and Murray, R. Radiographic and scintigraphic evaluation of
spondylosis in the equine thoracolumbar spine: a retrospective study. Equine Vet. J.
41, 2009, 800-807.
16. De Heus, P., Van Oossanen, G., Van Dierendonck, M.C. and Back, W. A pressure
algometer is a useful tool to objectively monitor the effect of diagnostic palpation by a
physiotherapist in warmblood horses. J. Equine Vet. Sci., 30, 2010, 310-321.
17. Kaigle, A.M., Sten, M.S., Holm, H. and Hansson, T.H. Experimental Instability in the
lumbar spine. Spine, 20(4), 1995, 421-430.
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spine during flexion-extension. J Spinal Disord., 11(2), 1999, 163-74.
Appendix 1
PHYSICAL EXAMINATION
Body Condition Score
Muscle Fitness score
Breathing
Heart rate
Temperature
Skin and coat
Mucous membranes
Lymph nodes
Examination of the equine back, including neurological and locomotion examination
Conformation (symmetry of pelvis, bones and muscles, also from above, lordosis/kyphosis/scoliosis):
Posture:
Hoof conformation:
Muscle
development
Neck
Atrophy
Normal
Hypertrophy
* compare left to right (and vv)
GAIT ANALYSIS
Walk in straight line:
Walk straight line and pull the tail:
Trot in straight line:
Walk an 8:
Turning short:
Walk a serpentine:
Walk backwards:
Walk and trot on hard circle left:
Walk and trot on hard circle right:
Thoraco Cranial
Thoraco Lumbar
Lumbo Sacral
Walk, trot and canter on soft circle left
Walk, trot and canter on soft circle right
NEUROLOGIC EXAMINATION
1. Houdingsreacties
Optische stelreflex
+
-
Labyrintaire + Proprioceptieve stelreflex
+
-
Dubbeltreden
+
-
Kruisreflex
+
-
Huppelreactie
+
-
Plaatsingsreactie
+
-
Oprichtreactie
+
-
Dreig reflex
+
-
Blink reflex
Pupillary light
reflex
+
-
+
-
+
-
Correctie reflexen
2. Cerebral reflexes
Strabismus
3. Spinal reflexes
Tail, skin, scrotum, withers
4. Vegetative reflexes
urinate/defecate
PASSIVE MOVEMENTS
Flexion
Extension
Lateroflexion/Rotation
Csp
Tsp
Lsp
Lsacral
* compare left to right (and vv)
FLEXION/PROVOCATION TESTS
* scaling from - (no difference/lameness) up to +++ (severe lameness)
Left front limb
Fetlock
Carpus
Elbow
Right front limb
Fetlock
Carpus
Elbow
Left hind limb
Fetlock
Tarsus
Hip/Knee
Right hind limb
Fetlock
Tarsus
Hip/Knee
Gaenlens Test (pelvic limbs + Lsacral + SIJ)
DSIC
HEAD, NECK AND BACK PALPATION
* scaling 0 (no reaction) to 5 (severe reaction)
Head
Superficial
Middle
Deep
Neck
Upper cervical (protocol Minnesota)
Superficial
Middle
Deep
Caudal cervical (protocol Minnesota)
Superficial
Middle
Deep
Withers
Superficial
Middle
Deep
Back (including epaxial and hypaxial regions)
Scapulothoracic
Superficial
Middle
Deep
Thoracic
Superficial
Middle
Deep
Lumbar
Superficial
Middle
Deep
Hindquarter
Superficial
Middle
Left
Right
Deep
Limbs
RF
Superficial
Middle
Deep
LF
Superficial
Middle
Deep
RH
Superficial
Middle
Deep
LH
Superficial
Middle
Deep
Grading overall tissue sensitivity:
COUPLED INTERVERTEBRAL MOTION
Left
Thoracic
Lumbar
Lumbosacral
Pelvis Lateroflexion/Rotion
Rib Costotransverse Joint/Costovertebral
BACKPAIN
YES
NO
Grading
1 (mild)
2 (moderate)
3 (severe)
0 (no)
Right