2. Less joint strength (Stability) during weight bearing phase of walking.
When an obese dog is walking or trotting, there is greater force bearing down on the leg touching the ground, and this forces a greater angle (flexion) or bend in the joints, making the joints less stable. Think of it this way…….as a human, we stand on just two legs, which is obviously different to dogs, but imagine standing with a 15kg bag of rice over your shoulders and you are asked to walk. With the heavier load, your knees are likely to bend more as you walk, as they take the force of the greater weight. Unfortunately, for the dog, it’s the elbow and the hip which suffer with less stability and strength in BOTH the swing (moving leg) phase and the stance (weight bearing) phase of walking motion. The elbow and hip are the two joints which are commonly affected with ‘dysplasia’ (abnormal joint structure) in the dog and later go on to develop osteoarthritis (degenerative joint disease).
3. Increased (compressive) force to the joint causes joint structure damage faster.
You probably already guessed it…….Heavier weight results in more force pushing down to the ground through the dog’s leg. There is up to 25% more force passing through the joint in an obese dog than in a lean dog. And greater force through the joints into the ground means greater compressive forces within the joints and more stress on the joint surface and structures which includes the cartilage and bone. This overworking of the joint with abnormal forces in turn will affect the rate of osteoarthritis development and progression.
The increase in body weight increases the compressive forces that pass through the joints to the ground. Blue= lean dog, Red= obese dog
4. Unnatural spine movement also occurs with excess body weight because some of the extra weight hangs downward off the supporting spine, around the belly. Between each of the vertebrae bones which make up the spine, and protect the spinal cord, there are many little tiny joints called facet joints. These little facet joints can also suffer from osteoarthritis causing back pain- the more weight, the more pain.