Musculoskeletal System - Healthy Dog Experts

The dog's skeleton is made up of 319 bones - about 100 more than humans have. Although the number of bones is roughly the same in all breeds, there is considerble variation in the size and shape of individual bones, as the result of selective breeding. The place where two bones meet is called a joint or articulation. In some joints there is a cushioning pad of cartilage interposed between the bones. This pad is called a meniscus. A damaged meniscus can deteriorate and inflame the joint. Abnormal wear and tear on joint surfaces and joint cartilages leads to arthritis. In many cases the adnormal wear and tear is the result of poor joint conformation associated with inherited orthopedic abnormalities such as hip dysplasia. Joint position is maintained by the ligaments, the tendons, and a tough fibrous capsule surrounding the joint. Together, these structures provide stability and hold the joint together. Joint looseness (called laxity) is caused by stretching of these support structures. Laxity enables the ends of the bones to slip partly out of position. When the joint capsule ruptures, the bones slip completely out of position. This is called dislocation. The skeletal anatomy of humans and dogs has much in common, including similar terminology. However, there are significant differences in the angles, lengths, and position of the bones. The dog's hock, for example, is actually the heel bone in humans. While people walk on the soles of their feet, dogs walk on their toes. Humans carry all their weight on their hips. Dogs carry 75 percent of their weight on their shoulders and front legs. Veterinarians, dog breeders and dog show judges use specific terms to describe a dog's overall composition and structure. Conformation is how the various angles, shapes and parts of the dog's body conform to the breed standard. Standards for purebred dogs describe the ideal conformation for each breed. These standards are based, to a certain extent, upon aesthetic considerations, but they also take into account the breed's original purpose as a working dog. Most breed standards provide some information on the desired angle or slope of the bones of the shoulders, pelvis and limbs. These angles are determined using imaginary lines drawn horizontally and vertically through the plane of the standing dog. Another term used to judge the physical attributes of a dog is soundness. When applied to the musculoskeletal system, it means that all the bones and joints are in correct alignment and are functioning as intended. In particular, in a dog with good skeletal conformation the alignment of the legs allows equal distribution of weight, equal bone pressure and equal strain on the supporting ligaments when the dog is standing naturally or moving at a trot.

Determining the Cause

Consider the history and circumstances surrounding the appearance of lameness. Did the lameness appear spontaneously or was there an injury? Which leg is involved? A dog often holds up the paw or places less weight on a painful leg, especially one that has been recently injured. A dog usually takes shorter steps on a painful or weak leg. You may notice that his head bobs or drops as his weight comes down on the painful leg. With chronic lameness, the dog may simply take very short strides with no obvious limp. This is also true if more than one leg is injured or hurts. The dog's head bobs up on the painful side and down on the side with the sound leg. Having identified which leg is involved, try to identify the specific site and possible cause. First examine the foot and look between the toes. Many cases of lameness are due to foot injuries such as sprains, pad lacerations, broken nails and penetrating puncture wounds caused by thorns and splinters. Carefully feel the leg from the toes up. Locate areas of tenderness by applying gentle pressure. You may also feel areas of swelling. Next, flex and extend all joints from the toes to the shoulder looking for resistance (lack of easy movement). Resistance is a sign of joint pain, which will be evident when the dog attempts to pull the leg free. if you aren't sure if something you feel is normal, check the dog's other leg. You have one for a comparison for both front and rear leg problems. Having located the site of pain, the next step is to try to determine the cause of the pain. Consider the following:

Infected areas are red, warm, and tender and are often associated with skin lacerations or bite wounds. There may be purulent drainage from the wound. The limp grows steadily worse. An abscess may be developing. The dog may have a fever. Dogs often lick at abscessed or wounded areas.

Sprains and strains occur suddenly and are often accompanied by swelling and bruising. Usually the dog is able to bear some weight on the leg. The lameness may persist for days or weeks.

Fractures and dislocations cause severe pain and the dog is unable to bear weight on the leg. There is some degree of deformity. The tissues are swollen and discolored from bleeding.

Inherited orthopedic diseases generally come on gradually. Young to middle-aged dogs are commonly affected. There may be few local findings to explain the lameness. Swelling, if present, is often slight. The lameness persists and grows worse with time.

Degenerative joint disease, also called arthritis or osteoarthritis, is the most common cause of lameness in older dogs. The lameness is worse when the dog wakes up and improves as he moves about.

Spinal cord injuries and peripheral nerve injuries produce weakness or paralysis without pain in one or more limbs.

Bone tumors are evidenced by a firm mass or swelling with or without signs of inflammation. Pressure over a bone tumor causes varying degrees of pain. Consider this diagnosis in a mature dog with an unexplained limp. Bone tumors are more common in large-breed dogs.

Diagnostic Tests

X-rays of the bones and joints are used to diagnose fractures and dislocations. They are also helpful in distinguishing bone growths from soft tissue swellings. Note that many cases of lameness occur without positive findings on conventional X-rays. A bone scan (also called nuclear scintiography) is an imaging technique that uses radioactive isotopes injected into the body and X-ray equipment to form a picture of the bone and surrounding tissue. These scans are especially useful in diagnosing bone cancers and determining the extent of their spread. Because of the cost and the restrictions on using radioactive isotopes, bone scans are performed only at medical centers and schools of veterinary medicine. A CT scan or MRI may be of benefit in special circumstances, particularly with tendon, ligament and muscle damage, but their availability and cost of these studies limit their usefulness. Synovial fluid is a viscous joint lubricant that contains hyaluronic acid. The fluid can be removed using a steril needle and syringe. Analyzing this fluid helps determine the cause of joint swelling. Normal synovial fluid is clear and pale yellow. Blood in the fluid indicates recent joint injury. Pus indicates joint infection (septic arthritis).

Bacterial contamination and subsequent infection is a hazard whenever bone is exposed. It occurs most often with open fractures. Other causes are gunshot wounds and animal bites that become infected and progress to adjacent bone. In rare cases osteomyelitis is caused by blood-borne bacteria or fungi. This occurs in dogs receiving chemotherapy and those suffering from illnesses that impair immunity. Signs of acute osteomyelitis are excessive pain, lameness, fever and swelling. In dogs with chronic osteomyelitis there is an intermittent purulent discharge through the sinus tracts connecting the bone to the skin. The diagnosis is confirmed by X-rays and a culture of the bone.

A sprain is an injury caused by sudden stretching or tearing of the ligaments in and around the joint, or the joint capsule itself. Signs are pain over the joint, swelling of the tissues and temporary lameness.

Tendons can be stretched, partly torn, or ruptured. Strained tendons follow sudden wrenching or twisting injuries. The tendons of the forepaws (front and back) are strained most often. The signs of a tendon injury are lameness, pain on bearing weight and painful swelling over the course of the tendon. Rupture of the Achilles tendon at the hock joint can be caused by sudden and extreme flexion of the hock. This injury tends to occur in Greyhounds, sporting and performance breeds. The Achilles tendon is the one most often severed in dog fights and car accidents. Rupture of the Achilles tendon causes a dropped hock. Inflammation of a tendon is called tendonitis. This injury follows strenuous field or road work and overuse of the limb.

Muscle strains are caused by stretching or tearing the muscle fibers or by overuse of a muscle following strenuous field or road work. Signs are lameness, swelling of the muscle, tenderness over the injured part and bruising. Bruising may be difficult to see beneath the fur.

A strong force is necessary to rupture a joint and displace the bones. Such injuries are usually caused by auto accidents and falls from a height. Signs of a dislocated joint are sudden pain and an inability to use the limb. The elbow or knee may be bent, with the leg pointing either toward or away from the body. The affected leg may be either shorter or longer than the opposite leg. It is important to realize that the soft tissues, such as ligaments, tendons and muscles are often torn or damaged as well. Simply replacing the bone may not be enough, because the support tissues that hold the joint together also need to heal. Subluxations (also called luxations) are dislocations in which the bones are only partly out of joint. Some subluxations are congenital, but most are caused by trauma. The limb does not shorten and joint deformity is minimal. Dislocations and subluxations affect the hips, stifles, shoulders, elbows and the small joints that make up the hocks and wrists. Subluxations of these smaller joints can be caused by a sudden force, such as jumping from a height.

The stifle joint is stabilized by a number of ligaments. The two large ligaments that cross in the middle of the joint are the cranial and caudal cruciates. The ligaments that stabilize the sides of the joints are the medial and lateral collaterals. The meniscus is a cushion of cartilage between the femur and the tibia and fibula. Rurute of the cranial cruciate is a common and serious injury of the stifle. It occurs in all breeds and all ages, but is more likely to occur in younger, active dogs. There may be a congenital or developmental predisposition in some dogs. If one tears, unless it is repaired, the ligament in the other knee eventually tears. The sudden onset of rear leg lameness suggests a rupture. The lameness may disappear with rest, then recur with exercise. In some cases the presenting sign is persistent lameness in one or both hind legs. The diagnosis is confirmed by palpating the stifle joint. In many cases the medial collateral ligament is also damaged. Rupture of the medial or lateral collateral ligament usually is caused by a severe blow to the side of the joint or a twisting motion, especially at speed. The affected ligament may be stretched, partially torn or completely severed. Diagnosis is made by manipulating the joint and looking for a degree of looseness. Severe blows to the stifle may also cause joint fractures. Dogs may need to be anesthetized for a thorough evaluation of the stifle. Injuries to the meniscus are associated with injuries to the cruciates. If a cruciate injury goes untreated, secondary damage to the meniscus occurs in the weeks and months to follow. The end result is degenerative arthritis and permanent lameness. Isolated meniscus injuries are rare in dogs.

Inherited bone and joint diseases have a genetic basis, despite the fact that only a certain number of offspring will be affected. If after a careful examination, one of these conditions is diagnosed in your dog, do not breed the animal.

Hip Dysplasia is the most common cause of rear leg lameness in dogs. The highest incidence occurs in large-breed dogs, including Saint Bernards, Newfoundlands, Rottweilers, Chesapeake Bay Retrievers, Golden Retrievers, German Shepherd Dogs, Labrador Retrievers and many others. Smaller breeds are also affected, but are less likely to show symptoms. Hip dysplasia is a polygenic trait. That is, more than one gene controls the inheritance. Environmental factors such as diet are also involved. The hip is a ball and socket joint; the ball is the head of the femur and the socket is the acetabulum of the pelvis. In a dysplastic hip, the head of the femur fits loosely in a poor developed, shallow acetabulum. Joint instability occurs as muscle development lags behind the rate of skeletal growth. As the stress of weight bearing exceeds the strength limits of the supporting connective tissue and muscle, the joint becomes loose and unstable. This allows for free play of the femoral head in the acetabulum, which promotes abnormal wear and tear. Feeding a very high calorie diet to growing dogs can exacerbate a predisposition to hip dysplasia, because the rapid weight gain places increased stress on the hips. Being overweight supports the genetic potential for hip dysplasia, as well as other skeletal diseases. A diet with an imbalance of calcium and phosphorus is bad for bone development. Another factor can bring on the symptoms of hip dysplasia is inappropriate exercise during the period of active bone growth. Young dogs should be discouraged from jumping up and down from heights in situations where they land on their back legs (such as jumping to catch a ball) and from standing on their back legs (which dogs do when they stand up against a fence or a window to get a better view). They should also avoid running on pavement. Dogs with hip dysplasia are born with hips that appear normal but progressively undergo structural changes. The age of onset is 4 to 12 months. Affected puppies may show pain in the hip, walk with a limp or a swaying gait, bunny hop when running and experience difficulty in the hind quarters when getting up. Pressing can cause the pelvis to drop. With the puppy on his back, the rear legs may not extend into the frog-leg position without causing pain. An X-ray of the hips and pelvis is the only reliable way of determining whether a dog has hip dysplasia. Good X-rays reuire the dog to be completely still to avoid giving the dog sedatives or anesthesia. The standard view is with the dog lying on his back with his rear legs parallel and extended. The knees (stifles) are rotated internally. Care is taken to be sure the pelvis is not tilted. Hip dysplasia is graded according to the severity of X-ray findings. In ideal hips, the femoral head fits tightly into a well formed hip socket with a minimum of space between the head of the femur and the acetabulum.The hip ball is almost completely covered by the socket. Normal hips are rated Excellent, Good or Fair on how closely they match the ideal. Dysplatic hips are rated Mild, Moderate or Severe. If the findings are not clear, the hips are rated borderline. In a dog with mild hip dysplasia, the X-rays will show mild subluxation (increased space in the joint) with the hip ball partway out of the socket. There are no changes associated with degenerative arthritis. In a dog with moderate hip dysplasia, the hip ball is barely seated into a shallow acetabulum. Arthritic changes begin to appear. These include wear and flatening of the femoral head, a rough appearance to the joint surfaces and the begining of bone spurs. In a dog with severe hip dysplasia, the head of the femur is completely out of the joint and arthritic changes are marked. Once arthritis is noted, the condition is irreversible. But even with arthritis some dogs are not lame. The onset of lameness is unpredictable, and some dogs may go the rest of their lives with dysplastic hips but no lameness. Others develop lameness as puppies.

Legg-Perthes disease is caused by a vascular necrosis of the femoral head. Avascular necrosis means death of bone in the head of the femur resulting from an interuption in the blood supply. It is not clear what causes this, but genetic factors may be involved. This disease occurs most often in toy breed puppies between 4 and 11 months of age. Large breeds are occasionally affected. Avascular necrosis occurs in both hips in about 15 percent of cases. Occasionally, it is a result of a traumatically dislocated hip caused by trauma such as an auto accident or a fall from a height. Weight bearing causes the dead bone beneath the cartilage of the femoral head to collapse. This fractures the cartilage and causes a gradual destruction of the hip joint. Signs are severe lameness and sometimes the inability to bear weight on the leg. Muscle wasting is pronounced and the joint loses some range of motion. The affected leg may be shorter. than the opposite normal leg. A standard X-ray of the hips and pelvis establishes the diagnosis.

The patella, or kneecap, is a small bone that protects the front of the stifle joint on the rear leg. The patella is anchored in place by ligaments and slides in a groove in the femur called the trochlea. If the groove is too shallow, the patella will slip out when the knee bends. When the patella slips out to the inside of the knee joint, it's called medial luxation. When it slips out to the outside, it's called lateral luxation. Luxating patella is usually an inherited developmental defect. Rarely, it is acquired through trauma. Medial luxation is more common. It occurs in toy, miniature and large breeds and is apparent in some puppies when they begin to walk. In others, it appears later. The patella may slip in and out of place, the affected leg is usually carried with the stifle joint bent and the foot turned inward. The condition is bilateral in about 25% of cases. Lateral luxation occurs in large and giant breeds at 5 to 6 months of age. A knock-kneed stance is the most noticeable sign. The foot often twists outward as weight is placed on the limb. Both knees are almost always involved. In the early stages, luxating patella may not be painful. But pain can increase as the grooves are polished smoother by the slipping action of the kneecap and as arthritis develops in the joint. The diagnosis of luxation is made by attempting to push the patella out of the trochlear groove. The degree of luxation is graded 1 to 4, depending on how easy it is to dislocate the patella and whether the patella returns spontaneously to the trochlear groove. This manipulation should only be done by a trained professional (doggy doctor) experienced in this technique.

Elbow Dyplasia

Elbow dysplasia is a common cause of front-leg lameness in large breed dogs. Breeds predisposed to elbow dysplasia include the Golden Retriever, Labrador Retriever, English Setter, English Springer Spaniel, Rottweiler, German Shepherd, Bernese Mountain Dog, Chow Chow, Chinese Shar-Pei, Newfoundland and others. The elblow joint is composed of the humerus, which articulates with the radius and ulna, and those two bones. The anconeal process unites with the ulna at about six months of age. It forms a curved depression in the ulna. The coronoid process forms part of the lower curved bone of the ulna. Dogs with elbow dysplasia have one or more of the following inherited developmental defects, which may occur singly or in a combination; ununited anconeal process, fragmented medial coronoid process, osteochondritis dissecans of the medial condyle of the head of the humerus and incongruity of growth rate between the radius and ulna resulting in a curvature of the radius. The first three defects are related to osteochondrosis. The fourth is related to an enlargement of the epiphyseal growth plate at the head of the radius. Signs of elbow dysplasia usually appear in puppies at 4 to 10 months of age, but some dogs may not show signs until adulthood, when degenerative joint disease starts. The signs consist of varying degrees of front-leg lameness that worsens with exercise. Characteristically, the elbow is held outward from the chest and may appear swollen. The diagnosis is made using detailed X-rays of the elbow joint, taken in extreme flexion. Radiologists are particularly interested in the appearance of the anconeal process of the ulna. In a dog with elbow dysplasia, the anconeal process has a rough, irregular appearance due to arthritic changes. Another sign of dysplasia is widening of the joint space associated with a loose, unstable joint. X-rays may be difficult to interpret before a pup is seven months of age. A CT scan may be required to demonstrate a fragmented coronoid process.

Bone lengthening is a continuous process in which rapidly growing cartilage at the ends of bones becomes calcified and is gradually incorporated into the bone. Osteochondrosis is a disease caused by a defect in the calcification process of this growing cartilage. In a dog with osteochondrosis, the cartilage is calcified in an irregular way instead of a uniform fashion. This creates areas of uncalcified, defective cartilage breaks into loose fragments called joint mice. This process, which is accompanied by joint pain and swelling, is called osteochondritis dissecans. Osteochondrosis most often involves the head of the humerus in the shoulder joint. It also occurs in the elbow, where it is responsible for many of the defects of elbow dysplasia. Osteochondrosis occurs less commonly in the stifle and hock joints. In the stifle, osteochondrosis involves the femur at its articulation with the tibia and the talus (the first bone of the hock). Osteochondrosis is a common disease of rapidly growing large-breed puppies. The first signs show up at between 4 and 8 months of age. The symptoms may resemble those of panosteitis, another disease that causes lameness in growing puppies. The typical presentation is gradual lameness that seems to stem from the shoulder, elbow, stifle or hock in a young dog of one of the large breeds. Lameness often gets worse with exercise. Symptoms may appear following a traumatic episode such as jumping down stairs. Pain is present on flexing and extending the joint. X-rays may show fragmentation of joint cartilage or a loose piece of cartilage in the joint. The diagnosis may not be made definitively until the dog is 18 months of age.

Panosteitis (Wandering Lameness)

Panosteitis is a disease of large, rapidly growing puppies between 5 and 12 months of age. The disease has been described in German Shepherd Dogs, Doberman Pinschers, Great Danes, Irish Setters, Saint Bernards, Airedale Terriers, Basset Hounds Miniature Schnauzers and other breeds. The cause is unknown, but inherited polygenic trait is suspected. Males are affected four times more often than females. Suspect this disease if your puppy exhibits intermittent lameness in one or more legs that is unrelated to trauma. A characteristic sign is the tendency for pain and lameness to shift from one limb to another over the course of several weeks or months. Thats why this disease is sometimes called wandering leg lameness. Pressure over a shaft of an affected bone elicits pain. X-rays show a characteristic picture of increased density in the affected long bone. Panosteitis must be distinguished from other causes of lameness in growing puppies, including osteochondrosis, elbow dysplasia and hip dysplasia.

Arthritis is a degenerative condition that affects one or more joints. Most cases occur in dogs with an inherited orthopedic disease such as osteochondrosis or hip dysplasia, or those with a joint injury. Some cases of arthritis are related to an immune-mediated joint disease or joint infection.

Osteoarthritis is a common disease that affects one out of five dogs during their lifetime. The problem is not confined to older dogs. Hip dysplasia, ruptured cruciate ligaments, patella luxation, joint trauma and other joint conditions can cause degenerative arthritis, even in young dogs. Large breed dogs are affected more often than small dogs. Heavy dogs are more likely to experience symptoms because of the extra strain placed on ligaments and joints. Dogs with degenerative arthritis experience varying degrees of lameness, stiffness and joint pain, which is more apparent in the morning and after getting up from a nap. They often exhibit irritability and behavioral changes associated with increasing disability. Cold and damp surroundings increase pain and stiffness. Degenerative arthritis is progressive and in time makes the dogs life miserable. The diagnosis is made by joint X-rays that show bone spurs at points where the ligaments and the joint capsule attach to the bone. There may be varying degrees of joint space narrowing and increased density of bone around the joint.

This is an unusual group of diseases in which antibodies are directed against the dog's own connective tissue, resulting in either an erosive or nonerosive arthritis. In erosive arthritis, cartilage and joint surfaces are destroyed. In nonerosive arthritis, there is inflammation but no tissue destruction.

Rheumatoid arthritis is an erosive arthritis that occurs primarily in toy breeds and other small breeds, such as Shetland Sheepdogs, at approximately at four years of age. It is characterized by morning stiffness shifting lameness and swelling of the smaller joints, particularly the wrists and hocks. Fever, loss of appetite and lymphadenopathy are accompanying features.

Nonerosive arthritis tends to occur in mid-sized and large-breed dogs at about 5 to 6 years of age. The cause is unknown. Signs are intermittent fever, loss of appetite, joint swelling and a lameness that often shifts from limb to limb. A form of nonerosive arthritis occurs with with systemic lupus erythematosus. The diagnosis of immune-mediated arthritis is made by joint X-rays and specific laboratory tests. Synovial fluid analysis helps distinguish immune-mediated arthritis from infectious arthritis and osteoarthritis.

Infectious diseases can produce arthritis. Rickettial arthritis is seen with Rocky Mountain spotted fever and canine ehrlichiosis and spirochetal arthritis with lyme disease. (All of these are tick borne diseases.) Fungal arthritis is a rare complication of a systemic fungal infection. Septic arthritis is caused by bacteria that gain access to joints with open wounds, soft-tissue infections around joints and via the blood stream. Injecting steroids into a joint carries a small risk of introducing bacteria.

Metabolic Bone Diseases

Hyperparathyroidism

The parathyroids are four small glands in the neck

located near the thyroid gland. The parathyroid

secrete the hormone PTH, which is essential to bone

metabolism and blood calcium regulation.

This disease is rare in dogs. It is caused by tumors of the parathyroid glands that cause them to secrete excessive amounts of PTH. Middle-aged and older dogs are affected. The average age of onset is 10. Keeshonds seem to have a breed predisposition to this problem. Signs are nonspecific and include loss of appetite, lethargy, excessive thirst and frequent urination. Constipation, weakness, vomiting, muscle twitching and a stiff gait have all been reported. The disease may not be suspected until a chemistry panel reveals a high serum calcium. A primary parathyroid hyperplasia syndrome, in which all four parathyroid glands are enlarged has been identified in German Shepherd Dog puppies. This is an inherited autosomal recessive trait. Anal sac adenocarcinomas have the unique property of producing PTH, and thus are a rare cause of pseudohyperparathyroidism. The diagnosis of primary hyperparathyroidism can be confined by measuring PTH. The serum PTH is above normal in dogs with this disease.

This is the end result of long-standing kidney disease that causes the body to retain phosphorus. The high serum phosphorus and low serum calcium stimulates the parathyroids to produce PTH. Symptoms similar to those of primary hyperparathyroidism are usually overshadowed by the kidney problem.

This disease (now rare) is caused by an excess of phosphorus or deficiency of calcium in the diet. Vitamin D is required for calcium to be absorbed from the small intestine. Thus a deficiency of vitamin D produces a deficiency of calcium. This can cause parathyroid glands to produce more PTH. One cause of nutritional secondary hyperparathyroidism is feeding a diet that consists primarily of organ meats, such as hearts, livers or kidneys. Such diets are to high in phosphorus and to low in calcium and all vegetable diets, corn bread diets and diets containing leftover table scraps. This disease does not occur in dogs who eat a nutritionally balanced diet. In puppies and young dogs, signs suggest skeletal problems and include lameness, bone pain, stunted growth and spontaneous fractures. In adult dogs, nutritional secondary hyperparathyroidism produces periodontal disease. Thinning of the jaws exposed the roots of teeth. The teeth then loosen and fall out.

Hypertrophic osteodystrophy is a developmental disease that affects large and giant breed dogs 2 to 8 months of age. This cause is unknown. Hypertrophic osteodystrophy targets the long bones close to the growth plates at the wrists and hocks. These areas become painful and give rise to lameness. The lameness ranges from mild to incapacitating. It often affects both front or both rear limbs. The bones are extremely warm, swollen and painful to the touch. Affected dogs are reluctant to move. Some dogs develop high fever, depression, loss of appetite and weight loss. Bone X-rays show enlargement of the affected growth plate. These findings distinguish hypertrophic osteodystrophy from panosteitis and other causes of lameness in growing pups.