Message Number: YG5381 | New FHL Archives Search
From: RRC
Date: 2001-07-11 13:06:00 UTC
Subject: Bob C: Ferret Vertabrae

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