Bones and Joints
The skeleton is the frame that supports and protects the muscles and other soft tissues. It also stores minerals the body needs, such as calcium. The leg and pelvis bones contain bone marrow, which produces the red and white blood cells the body needs to function. Bone is a living, renewable component of the body that contains blood vessels and nerves. It's covered with a thin sheath of sensitive tissue, the periosteum, which plays a role in bone growth, repair, and protection.
The joints are the areas where two bones meet. Your dog's major joints are the knees, hips, and elbows. The joints are cushioned by cartilage, a specialized type of connective tissue.
The skeletal system has two major parts. The appendicular skeleton is made up of the leg and pelvis bones (known as the long bones), and the axial skeleton consists of the skull, vertebrae, ribs, and sternum. The long bones have growth plates that produce cartilage, which is converted to bone as the dog grows. At puberty, this bone growth slows, and the growth plates close when the dog reaches physical maturity, allowing no further growth.
A dog's body has 319 bones. That's about 100 more bones than humans have. Whether they're big or small, all dogs have about the same number of bones, although the size and shape of the bones do vary.
The skeleton is the framework that supports the body. More than 300 bones make up the canine skeleton.
Puppy Skeletal Development
Depending on the breed, a puppy's bones continue to grow and develop until he's anywhere from a year to two years old. He'll grow rapidly until he's about six months old and then more slowly with occasional growth spurts, until he reaches physical maturity. Small and medium-size dogs mature at about seven months to one year of age, while large and giant-breed dogs might not be fully grown until they're eighteen months to two years old. You'll notice that your dog goes through a gangly stage — often referred to as the ugly period — usually between six months and two years of age. He might look higher in the rear than in the front, for instance, but eventually everything will all come together. He might be three or four years old before he has the complete body and muscling of a mature dog.
Dogs are prone to a number of diseases that affect the skeletal system, resulting in lameness or bone deformities. These diseases can be congenital, hereditary, infectious, or inflammatory, metabolic, traumatic, or neoplastic. A congenital disease is one a dog is born with. Hereditary conditions are passed on from one or both of the parents. Infectious or inflammatory diseases can be caused by injury, degeneration from age, or bacterial contamination of a joint through a wound. Metabolic diseases result from too much or too little of a particular hormone or other substance in the body. Traumatic injuries include getting hit by a car and breaking a leg. Neoplastic diseases are caused by cancer.
The most common skeletal disorders are hip dysplasia, intervertebral disc disease, patellar luxation (all hereditary), and arthritis (inflammatory). Hip dysplasia occurs when the head of the hip bone doesn't fit properly into the hip socket. The resulting looseness of the joint causes inflammation, pain, and lameness. Intervertebral disc disease, known as IVDD, is a ruptured disc (the cushion of cartilage between each vertebrae) that puts pressure on the spinal cord or a nerve root. Some skeletal disorders, such as patellar luxation (dislocation of the knee), are easily diagnosed simply by observation of the dog's hoppity gait and range of motion. Others require X rays or other diagnostic tests. Sometimes they can be corrected surgically, but often rest and pain relief are the only treatments available, especially for such conditions as arthritis.
You can help reduce the risk of your dog developing a skeletal disorder by purchasing your puppy from a reputable breeder who makes sure all breeding stock tests clear of skeletal problems. Also, not over feeding your puppy or adult dog, and preventing your puppy from doing a lot of jumping or running on hard surfaces before his growth plates close help reduce the risk of developing a skeletal disorder.