Intro to canine and feline anatomy and physiology

Head and Shoulders, Knees and Toes.

Hi everybody! Today we are going to spend a bit of time learning more about the anatomy (parts) and physiology (function) of cats and dogs. In essence, the anatomy of our furry friends is very similar to our own anatomy. But there are several very important differences that can contribute to the development of injuries and arthritis.

We’ll cover some vocabulary and there will be plenty of pictures, and we’ll end with a sneak peek at next week’s topic.

Which way is up? – Anatomical Directions

For the most part, using specific words to describe anatomical directions is important for medical records but doesn’t seem to matter as much when talking about your pet. However, it can be helpful to standardize how we talk about exercises.

• Proximal: closer to the torso
  • Ex: The shoulder is proximal to the elbow.
• Distal: farther from the torso
  • Ex: The toes are distal to the knee
    
• Cranial: towards the head
  • Ex: The shoulders are cranial to the hips.
• Caudal: towards the tail
  • Ex: The pelvis is caudal to the ribcage.

Why can’t it just be called an ankle? – Anatomical Terms

Most of the body parts of cats and dogs have the same names as in humans  (yes, the back legs have knees and the front legs are really “arms”), but some have different names despite serving the same purpose. We’ll focus on a small number of terms that you might hear from me or your other veterinarian(s) – otherwise the list could go on forever.

SPINE

• Cervical spine: the neck.
• Thoracic spine: the portion of spine with ribs attached.
  • TL Junction: where the thoracic and lumbar vertebrae connect.
• Lumbar spine: the “lower back,” connecting the ribs to the pelvis.
  • LS Junction: where the lumbar vertebrae connects to the sacrum.
• Sacrum: the short segment of the spine which connects to the pelvis.

FRONT LEG – also referred to as a forelimb. It has the same anatomy as your arm.

• Shoulder: the most proximal joint of the forelimb.
  • Dogs and cats don’t have functioning collarbones. Their forelimbs are only attached to their torso by muscle.
• Elbow: this hinge-like joint lines up with the ribcage.
  • When your pet lies down in “sphinx pose” the elbows become very prominent.
• Carpus: the WRIST.
  • If you make “t-rex arms” you can appreciate the way your pet’s carpus moves.
• Digits: the TOES.
  • Your pet walks with a digitigrade stance. This means they walk on their “toes” but their “palm” does not contact the ground.

BACK LEG – also referred to as a hindlimb. It has the same anatomy as your leg.

• Hip: the most proximal joint of the hindlimb.
  • The hindlimb is attached to the body by bony connection to the pelvis and spine.
• Stifle: the KNEE. 
  • This joint points forwards when your pet is walking, just like your own knee. 
• Tarsus or hock: the ANKLE.
  • The bony part of your pets hind leg that points backwards is the HEEL.
• Digits: the TOES.
  • Similar to the front foot, your pet walks on its “tiptoes.”

What next, Dr. Frankenstein? – Putting it all together to understand physiology 

Let’s see how these things can come together to lead to some of the common conditions we encounter in dogs and cats. We’ll cover these in more depth in future lessons, but at least we can start thinking about these conditions now.

Back Trouble

• Think about the way that gravity works on your spine: in general your spine is a vertical column with your head on top and your pelvis on the bottom.
  • Now think about your pet’s spine: a horizontal column supported in the back by the pelvis, with muscular support at the shoulder and a head hanging off the front. So, clearly the stresses are quite different.
  • Next, add in genetics and breeding: some breeds are genetically predisposed to abnormal vertebrae or abnormal intervertebral discs. These can include Dachshunds, French Bulldogs, Doberman Pinschers, Great Danes, and many other breeds. 

• We’ll cover this topic in much greater depth later. Here’s the quick version:
  • The discs between vertebrae can bulge into the spinal canal and cause pain and disruption of nerve signals.

Bum knees

• Why do so many dogs have knee issues? There are many components but to simplify, we’ll think about two main categories and the related anatomy:

• CCL
  • Your knee is a fairly flat hinge with your body on top. The ACL (“cruciate”) keeps things centered and stable.
  • Your dog’s knee – especially medium to large-breed dogs – often has a slope to it. When they bear weight, the thigh bone wants to slide backwards and the shinbone wants to slide forwards. The CCL (“cruciate”) tries to keep everything centered but the stress is too much. A rupture can result. Ouch!
    
• MPL
  • In small-breed dogs, genetics and environmental factors can lead to abnormalities of the shape of the front of the thigh bone. This can let the patella (“kneecap”) slide out of place. When this happens, the hinge function of the knee is altered – until the patella slides back into place. 

Loose hips

• Hip dysplasia: dysplasia means abnormal development.

• Hip dysplasia quite literally means that as an animal is growing, the hips are not developing normally. This condition is often genetic, although environmental and traumatic factors can be considered as well. 
• Abnormal development of the acetabulum (“hip socket”) or head of the femur result in a poorly aligned ball-and-socket joint. Instability causes pain, damage to the cartilage of the joint, altered gait, and ultimately arthritis.

Iffy elbows

• Another genetic condition! Although trauma can contribute, many dogs with elbow dysplasia have a genetic predisposition which causes their ulna, radius, and/or humerus to grow abnormally. This leads to poor alignment of the hinge joint of the elbow, which causes pain, damage to the cartilage of the joint, altered gait, and ultimately arthritis.

Ouch, osteoarthritis

• We can all think of someone with arthritis. Creaky joints, achy bones, hard time getting up and down. But what is really going on?
  • Arthritis means inflammation of the joints. There are two main ways this can happen:
    • Normal forces through abnormal joints:
      • This happens with hip dysplasia, knee issues, elbow issues, fractures, etc
    • Abnormal forces through normal joints:
      • This sort of thing happens with repetitive stress injuries. 
        
  • Okay, so now that we know the process, let’s think about the effects:
    • Regardless of the process, inflammation occurs. Inflammation hurts. Chronic inflammation in the joints leads to changes in the appearance of cartilage, bone, and connective tissue. This is why you can imagine the knobby fingers of someone with severe arthritis in their hands. 

These conditions are some of the most common that we see causing discomfort and decreasing quality of life in aging pets. Acupuncture, physical rehabilitation, laser therapy, and PEMF therapy can all play a role in keeping your pets comfortable and helping them Age Gracefully. 

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Thanks so much for sticking through to the end of this lesson! Come back next week to learn about Signs of Pain in cats and dogs!

Is it a struggle to get your dog into (or out of) the car? Do you find your cat unable to reach its favorite windowsill? Is your pet sleeping a lot and avoiding play?

If you answered yes to any of these questions, “Signs of Pain” should be a very useful read. See you next week!