Breed conformation has never before been scrutinised with such
intensity as in the light of recent events and while this may at
first appear to be an intrusion in to the hallowed ground of breed
standards, the welfare of the dog must be paramount. Selective
breeding for the different traits that make up individual breeds has
also allowed less desirable traits to inadvertently occur. In the
orthopaedic world the big three problems are hip dysplasia, elbow
dysplasia and cruciate ligament rupture or disease, and undoubtedly
these are basically conformational problems although defining the
exact causes is difficult.
A
more recent conundrum is the significance of the sloping topline in
the German Shepherd Dog breed with regards to gait and lameness and
before any discussion, it is well to remember the lines of the
philosopher Hippocrates in 360 BC when he said “There are in fact
two things:- science and opinion. The former begets knowledge, the
latter ignorance.” Evidence-based science is, where possible, on
what judgements should be made.
A
sloping topline is a term that needs defining to prevent any
misunderstanding and in this context it is a sloping back line from
the shoulders or withers down to the pin bones of the pelvis. This
is evident with the dog at the walk or in the natural stance.
Dogs with low croups have limited extension in their hock joints.
Most breeds of dog have hock joints with approaching 180 degrees of
extension whereby the foot can be brought into line with the tibia
or lower limb. Many German Shepherds can only achieve something like
150 degrees of extension and it is mechanically impossible to
increase the extension angle (figure 1). This results in increased
hock flexion which in turn also increases the flexion of both the
stifle and hip joints causing the pelvis to be closer to the ground.
To understand this better try standing on tip toes in a crouched
posture. When moving from a crouch to an upright position, the
ankles, knees and hips all extend together, and then flex together
when crouching.
The
next piece of evidence is that German Shepherds are more prone to
hip arthritis than other breeds. The PennHIP method of assessing hip
dysplasia is based on measuring the looseness or laxity of the hips
and the degree of laxity is objectively measured and is called the
distraction index. The distraction index reflects the likelihood of
the dog developing osteoarthritis of the hips later in life. In the
graph below (figure 2) the sigmoid curve of the German shepherds
shows a higher tendency to develop osteoarthritis by two years of
age than the curves of the other three breeds.
It
is postulated that this is due to the altered biomechanics of the
hip joints from weight-bearing with more hip flexion.
With this logic a sloping topline causes an increased risk of
developing hip osteoarthritis and it is therefore undesirable.
Osteoarthritis will not occur however in dogs that are free from hip
dysplasia that have tight hips and this means a distraction index of
ideally less than 0.3. Unfortunately using low BVA/KC hip scores
will not guarantee staying free of osteoarthritis. A paper soon to
be published shows that greater than 50% of dogs scored as excellent
under the OFA hip scheme in the USA (this is similar to the BVA/KC
scheme) went on to develop osteoarthritis.
The
other question asked about the sloping topline is its influence on
the biomechanics of the spine as German shepherds are prone to
degenerative intervertebral disc disease that can cause hind limb
weakness and a wobbly gait. The answer to that question is unknown
and would be opinion only. CDRM or degenerative myelopathy is a
totally different disease and is not influenced by conformation.
On
a more positive note German Shepherds have a low incidence of
cranial cruciate rupture and disease when compared with other common
breeds of similar size. It is postulated that this is due to the
increased flexion of the stifle that alters the functional tibial
plateau angle (this is all technical jargon and is outside the scope
of this article).
Therefore if the sloping topline is bred out maybe cruciate
problems with resultant stifle osteoarthritis will be substituted
for hip osteoarthritis!
Figure 1. This shows the
maximum extension of the hock of a German Shepherd Dog.
Figure 2. This graph shows the probability of a dog of one of
the specified breeds developing osteoarthritis of the hips by two
years of age. The German Shepherd Dog has a greater tenancy than the
other breeds.
Note that DJD is short for degenerative joint disease and is
the same as osteoarthritis.
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