Dogs’ toenails are made of modified epidermal (skin) cells. These cells form the toenail structure which includes a sole, two walls and a thicker ridge on top that gives the nail the pointed appearance. Nails grow from the third or distal phalanx bone of the dogs’ toes.

Dog’s nails grow very rapidly, approximately 1.9 mm per week and need to be worn down naturally or trimmed to avoid the dangers of overgrown nails. (Evans and de Lahunta 2013, Kainer & McCracken 2003)

What are the dangers of overgrown toenails?

Ingrown nails

Left untrimmed dog’s nails will continue to grow in a circular fashion, until the nail grows into the base of the nail or the pad of the foot. This can occur with dew claws and toenails. If you are not comfortable with trimming nails once they have reached this point, it is probably a good idea to visit your vet, particularly if the nail has penetrated the skin.

Effects on dog’s movement

As you can see from the image of the dog’s paw for this blog, the phalanx bones of the dog’s digits (toes) are normally quite angulated (when the nails are not overgrown) and provide points of attachment for the lower limb muscles. The paw structure including the skeleton, muscles, tendons and ligaments enables the dog to weight bear through the pads of their feet.

When the dog moves, it exerts forces on the ground to bear their weight and to propel them forward. These forces are referred to as ground forces and they are greater in the forelimbs than the hind limb. When moving, forces are transmitted almost evenly over the paw. The dog’s weight shifts marginally from the back of the paw to the front and from the inner edge to the outside. (Fischer & Lilje 2014)

In movement the role of dogs’ paws are critical as “shock absorbers” and to complement the movement of the limbs. Paws counter gravity and stabilize the joints on touchdown. They also help compensate for uneven ground. The flexor and extensor muscles support the limbs through the stance phase of the gait and prepare the limb for protraction or retraction. (Fischer & Lilje 2014)

Further, the dog’s ability to accelerate or slow their movement depends on the relationship of the limbs to the body’s central of mass. When standing a dog’s centre of mass is typically over its sternum. (Fischer & Lilje 2014)

When the toenails are overgrown (i.e. they are touching the ground), the effects on the dog’s ability to move properly can be profound. Some of the effects are discussed below.

1. When the nail touches the ground, it decreases the angulation of the phalanx bones. The paw appears splayed or “flattened”. This action stretches and strains the ligaments holding the bones in place and the tendons attaching the muscles. While tendons have high tensile strength, they have limited elasticity so long term strain can easily result in injury.

2. Muscles work in groups, so if some muscles in the lower limbs are not working properly this disproportionately loads other muscles in the shoulder and hip joints, leaving them prone to overuse and injury.

3. As the toenail contacting the ground changes “alignment” of the paw, the ability of the paws to act as shock absorbers and stabilise the dog in movement is compromised. The effect being that the dog may be tentative on uneven ground, resists running or trotting or incurs a jarring injury as their paw is not weight bearing properly on touchdown.

4. When the angulation of the bones in the paw changes, the dogs’ centre of mass moves toward the tail. Changing the centre of mass affects the dogs’ gait which loads muscles in abnormal ways, making them prone to overuse and injury.

How do you know when to trim your dog’s nails?

If the toenail is contacting the ground when the dog is in a stand this is usually a good indicator that nails need to be trimmed. If you, like me have tiles or hard floors, I know that if I can “hear” my dogs as they walk around, then it is toenail trimming time.

Full Stride provides massage treatment to restore pain-free mobility in dogs with strained or injured muscles. Please feel free to contact me at jlconlon@fullstride.com.au to discuss how I may assist you and your dog.

You can also stay up to date by following Full Stride on Facebook – https://www.facebook.com/FullStrideCanineMassageTherapy/

Until next time, enjoy your dogs.

Sources:

Evans, Howard and de Lahunta, Alexander (2013), Miller’s anatomy of the dog 4th edition, Elsevier Saunders, St Louis, Missouri, USA

Fischer, M.S & Lilje, K. E, 2014 Dogs in motion, 2nd edition, VDH Service GmbH, Dortmund, Germany

Kainer, Robert A & McCracken, Thomas O 2003, Dog Anatomy: A Coloring Atlas, Telon New Media, Wyoming USA.