[Posted in 4 parts, combined here into one. BIG]
This snip was anonymously forwarded to me with a request for "elaboration
and explanation of pathology". Was it from the FHL?
>...
>I took him in for a radiograph and found out he has a fused extra sacral
>vertebrae.He does have problems getting around but not all the time. Is
>there something else that I should be concerned about? My vet doesn't
>seem to think so but my instincts tell me different. any info would be
>wonderful! K.M.
I don't get many questions that specifically relate to what I am trained to
do, so if I ramble, please forgive me. I love being a zooarchaeologist and
working with animal skeletons. That passion generally manifests itself in
excessive verbiage. I apologize beforehand.
Unless a vet has noticed a specific pathological problem with the bone
(malformation, some sort of extra growth or tumor, obvious nerve problems,
etc.), the presence of an extra vertebra is nothing to be concerned about.
Within the restraints of the prior caveat, chances are that if a locomotor
problem is due to the extra fused vertebra, any difficulty would have been
apparent from early in development rather than suddenly now causing
problems. With the exception of sacral vertebrae, no other fused vertebrae
are normally found in the ferret. While the presence of fused (non-sacral)
vertebrae is a pathological condition, it doesn't necessarily follow that
it means the ferret is in pain, is suffering from nerve problems, or even
notices a restraint of mobility. I see fused vertebrae in ferrets and
other animals all the time and quite often no one has the slightest clue
that they were even there.
Ferrets, either through the process of domestication or because vertebrae
are variable in most mustelids anyway, theoretically have a set number of
vertebrae, However, in the real world they are quite variable in number.
The shorthand for the vertebral formula of ferrets and polecats is listed
in several zooarchaeological handbooks as: C7 : T15[14-16] : L6[5-8] :
S3[3-5] : Cd 18[15-20], and my personal study of several hundred ferret
and polecat skeletons do not contradict this finding. Codes are: "C"
Cervical, "T" = Thoracic, "L" = Lumbar, "S" Sacral, "Cd" = Caudal. When
you see a "7", it means there are seven vertebrae that do not vary in
number (except in pathological specimens). When you see "15[14-16]", it
means most individuals have 15 vertebrae, but some can have as few as 14 or
as many as 16, and the extra vertebrae are NOT considered pathological. So
a ferret with only 5 cervical vertebrae (normal = 7) would be considered
pathological, but if they had 16 thoracic (normal = 15, but range from
14-16), it would be considered anatomically curious, but normal. "L1"
means the first lumbar vertebra, counting from the head towards the tail;
"T3" would be the 3rd thoracic vertebra. Vertebral formulae are based on
the study of a large number of individuals, and are not only used in
species identification, but are also important in determining evolutionary
relationships.
All mammals start out with roughly the same number of undifferentiated
vertebrae; at least as an embryo. The first 2 or 3 fuse together to help
form the rear and bottom of the skull. The next 7 form the neck bones,
or cervical vertebrae. In some mammals, including marine mammals,
armadillos, sloths, and anteaters, the cervical vertebrae may be greatly
reduced, fused together, or both, but they are actually all there at
some point in time. On occasion, the 7th (or last) cervical vertebra may
have one or two tiny ribs, called cervical ribs. They often look like
separate portions of the transverse process, but can take on the
appearance of a first rib. While they may slightly reduce mobility, they
are generally considered harmless and more of an anatomical curiosity
than anything else.
Thoracic vertebrae are defined by the presence of ribs and by forming
the thoracic cavity, which contains the heart and lungs. As already
mentioned, not all vertebrae with ribs are thoracic; it is not uncommon
for cervical ribs to be present between C7 and T1, as well as lumbar ribs
at L1 or even L2. These vertebrae are not redefined as thoracic because
they do not form part of the thoracic cavity and because the presence of
the ribs is atypical. Most mammals have between 12 and 15 thoracic
vertebrae, although species with less or more can be found. Extra or
missing thoracic vertebrae are generally anatomical curiosities only; not
a problem.
Lumbar vertebrae support the lower back, and in quadrupeds are massive in
comparison to the other vertebrae. The size allows for large muscle
groups which flex the back to aid in running, as well as to support the
contents of the abdominal cavity. Lumbar vertebrae are simply defined as
residing between the sacrum and the thoracic vertebrae. Lumbars are one
of the most variable of the vertebral groups in number, ranging from as
few as 5 to as many as 8 in ferrets and polecats. Generally, when you
notice the number of lumbar vertebrae are few, it means the number of
sacral and/or thoracic vertebrae are many. In other words, many times
when a ferret has only 5 lumbar vertebrae, they will have an extra
thoracic or sacral, making up the difference. This isn't always the case,
but I have commonly noticed it in my skeletal studies of ferrets and
polecats. Sometimes a lumbar vertebra will be partially fused to the
sacrum, generally on one side only. This sacralization of the lumbar is
not uncommon in domesticated ferrets, but I have never seen it in polecats
or black-footed ferrets. It doesn't appear to cause any problems, and is
considered an anatomical curiosity, rather than a pathological condition.
Sacral vertebrae fuse to form the sacrum, which provides support for the
pelvis. Together, the sacrum and pelvis create a sort of box which
supports the weight of the body over the lower limbs. While the sacral
vertebrae are fused together, the sacrum doesn't actually fuse to the
pelvic bones (except in a few species), but are instead held in place by
a combination of extremely strong ligaments and rough joint surfaces.
Ferrets generally have 3 sacral vertebrae fused into a single bone, but
finding 4 fused together is not unusual. I have seen two instances where
the sacrum is composed of a total of 5 fused sacral vertebrae. As already
mentioned, sometimes a lumbar vertebra will partially fuse to the sacrum,
as will one or more of the caudal vertebrae. When four sacral vertebrae
are present, it is almost always a case of sacralization of the last lumbar
vertebra. Again, this occurs frequently enough to be considered anatomical
curiosities rather than an actual pathology.
Caudal vertebrae are the bones which make up the roof of the pelvic canal
and the tail (coccygeal is reserved for humans; the coccyx is composed of
3 or 4 fused coccygeal vertebrae). These vertebrae are highly variable in
number and when most references say the ferret has 18 of them, it is an
average based on a large population sample. The caudal vertebrae are
identified by the lack of the large hole found in the other vertebrae which
surrounds and protects the spinal cord. The first few caudal vertebrae
have some tiny bones called hemal arches (chevrons) which help protect the
blood vessels and nerves which run under the tail. Fused caudal vertebrae
are quite common and are generally a pathological condition secondary to
injury or infection. As long as the ferret has recovered from the insult
(commonly a fracture or crushing type of injury), and there is no
infection, the fused bones present no problem. As you go down the tail
towards the tip, the caudal vertebrae get thinner and smaller; the last
caudal vertebra is usually no larger than the point of a pencil or smaller.
I have found the last 2 or 3 caudal vertebrae to be fused in many
instances.
Sometimes the cranial and caudal maxillary processes on the lumbar
vertebrae will grow together so tightly that they seriously restrict
side-to-side and/or up-and-down movements (in a cleaned skeleton, the bones
remain hooked together and cannot be separated without fracturing). The
processes are not fused and arthritis is not necessarily present; rather,
the edges of the bone tend to curl over each other, restricting movement.
I do not know if this is painful to the ferret, but doubt if it is. What
probably *IS* painful are arthritic lipping and spurs on the various
articular surfaces, which are quite common in nearly every older ferret
skeleton I've studied. Frequently, one or more of the transverse or
spinal processes are inflated, probably as a result of crushing, fracture
or infection. Older ferrets seem to commonly suffer from at least a
minor degree of spondlyosis, especially in the lumbar and lower thoracic
vertebrae and between the sacrum and last lumbar vertebra, but I have
only seen a single instance where it has resulted in serious ankylosis.
The most common pathologies I have noted are osteoporosis, infections, old
fractures and cancerous bone growths. I don't know how common bone cancer
is in ferrets, but I have seen three instances where cancers have invaded
vertebrae in the skeletons I have studied. Minor vertebral fractures are
more common than you might think, especially of the spinal or transverse
processes. I suspect many of these occur as a result of being stepped on,
or damaged when kits. In a single instance, I have seen a healed fracture
of a T5 centrum, but do not know if the ferret had spinal cord damage or
not. Bone infections are also more common than you might suspect, but in
the vertebrae are usually limited to the various processes.
By far, the most common bone pathology I've seen in ferrets is
osteoporosis. It is so common, it took me quite a while to realize I was
actually looking at a pathology. It wasn't until I had studied a couple
hundred feral ferret, polecat and black-footed ferret skeletons that I
realized pet ferrets had abnormally low bone density. In some skeletons,
pet ferret skeletons have a density 40% that of a feral ferret or polecat.
Some loss of density can be attributed to cancers (when present), which
suck up calcium from the tissues. Some can be caused by neutering, which
causes a sort of "artificial menopause" in both male and female ferrets.
Some osteoporosis could be caused by diets deficient in calcium phosphates
(or having them in the incorrect ratio), steroid use, or even from
long-term inactivity due to being caged, or inactivity due to chronic
illness. One thing I have noticed is that ferrets with long term adrenal
disease seem to have lost a great deal of bone density, even to the point
where the centrums of vertebrae have collapsed.
There are other, less common bone pathologies which can be found in the
vertebrae, but I will not discuss them now because of their infrequent
nature. If anyone has specific questions or desires book references which
might be of interest, let me know.
Bob C
[Posted in FML issue 3476]
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