By Helen M. Hislop, PHD
Another of the many disorders shared by man and dog is a condition which affects the hip joint, causing a limp, pain and deformity of the joint. It is called Legg-Calve-Perthes disease, though commonly the middle name is omitted.
As with many disease this condition is known by the names of the physicians who first described it (Legg in England, Calve in France and Perthes in Germany). A more descriptive names is avascular necrosis of the head of the femur. It also may be called toxa plana, osteochronditis deformans juvenilis; or aseptic necrosis of the femoral head.
HOW DOES BONE GROW?
The normal adult hip joint (in man or dog) is formed from two fully ossified bones, the thigh bone (femur) which has a dome-line head that fits snugly into a rounded hollow receptacle (the acetabulum) in the pelvic bone. (Fig 1). But bone are not fully occified at birth or for some time thereafter. This you well-know because the sutures in the skull remain open until full head size is reached so that the brain can attain its mature size ... and only then do these cranial sutures (or fontanels) close or ossify. Long bones start as cartilage and gradually ossify beginning in prenatal life. For example, the long femur begins to ossify in the puppy at about the 35th day of fetal life but this ossification occurs only in the shaft (diaphysis) (Fig 2) of the bone while the ends of the bone (epiphyses) do not ossify (i.e. close) until some time in late puberty. The acetabulum (hip socket) on the other hand does not ossify at all prior to birth but begins that process when the pup is about 3 weeks into post-natal life. If for any reason the epiphyses (growth plates) close early, growth will be stunted. Very early closure of the long bones of the limbs results in dwarfism and is the cause of the short legs in the Welsh Corgi. Another bit of anatomy it is important to understand is the circulation to the capital femoral epiphysis. Two very small arteries branching off the extracapsular arterial ring (Fig 3) are the only blood supply to this important bone-growth center. Most of the recent research has focused on studies to occlude or disrupt this vascular supply. Indeed when this has been done, there arises a syndrome very like Legg-Perthes. (4.6)
WHAT IS LEGG-PERTHES DISEASE?
The growth center concerned with Legg-Perthes (L-P) is called the capital femoral epiphysis (Fig 2) When this growth plate is fully ossified (about 6-8 months of age in terriers; much later in large breeds) it forms the spherical head of the femur (Fig 1) and blends with the neck and shaft of the bone.
There are a number of disorders which affect primary and secondary ossification centers which, as a group, are called the osteochondrosis. Legg-Perthes falls into this classification. Legg-Perthes is one of the most common hip diseases in children. It certainly is common in dogs but no total incidence figures are available. Despite its relatively frequent occurrence, it remains on of the most confusing and poorly understood disorders.
What happens is that sometime prior to ossifications, the capital femoral epiphysis begins to degenerate for reasons that are not entirely clear. The mechanism is believed to be the same in both children and puppies, causing pain and a limp. The best evidence suggests that the arterial circulation to the femoral head is lost or compromised leading to necrosis (tissue death).
IS LEGG-PERTHES INHERITED?
The possible genetic nature of this hip disease remains obscure and most probably there are multiple factors that lead to the clinical onset. It is well established that families of children with Legg-Perthes exhibit an increased incidence of this disorder that may be as low as 2% or as high as 20% (2) Nonetheless, there is no consistent pattern of inheritance in the human just as no pattern has been found in dogs. The conclusion is that the inheritance pattern is multifactorial with a major determinant occurring before epiphysis closure. What makes the human studies confusing is a lack of reporting the degree of relationship (eg. a 1st degree is parent/siblings while a 2nd degree relation is cousins, etc). With pedigrees so carefully maintained in the dog this problem could be overcome if breeders would tackle a carefully designed study.
One study in 1978 of 310 children with Legg-Perthes did show that pregnancies were normal but birth weights were low and abnormal birth presentations were more frequent than the norm. (1) Parents of the L-P children were older and the child was rarely the first. In humans, males are more commonly affected than females (5:1) and associated abnormalities include undescended testicles, renal problems and inguinal hernials. Affected children generally are shorter than their age-counterparts and bone age may be as much as 3 years behind chronological age (3).
In the dog, miniature conformation (as in the miniature poodle) may contribute to L-P since such breeding includes sexual precocity which gives rise to early cessation of bone growth (4). The literature is meager in breed reports or other genetic studies that might shed light on inheritance in the dog. Legg-Perthes is, however, virtually unknown in the mongrel (6) It is cited as not uncommon in the West Highland White and in the Wire Haired Fox Terrier and as rare in the Jack Russell Terrier (6). It is found in the Miniature and Toy Poodle, the Miniature Pincher, the Brussels Griffon, the Miniature Schnauzer, in Dachshunds, Chihuahuas, Pekes and Poms…but it must be emphasized that incidence data are not reported for these breeds. Whittick also lists "terriers" but does not break out separate breeds (5). Whittick further claims no sex difference in the dog but did not cite the source of his data (5)
The influence of environment on the incidence of L-P is obscure. Children from lower socioeconomic groups have a much higher incidence which could suggest nutritional factors or other unidentified environmental influences.
TRAUMA AS A PREDISPOSING CAUSE
Trauma is the most often cited environmental factor as a precursor to L-P. In many well-documented cases the onset of limp has not been associated with observed trauma (such as seeing the puppy fall off the bed). In other cases the owner can recall a specific traumatic event to explain onset of a limp. Retrospective history is not very reliable because puppies are subject to many minor traumas of which some are followed by L-P, others are not. In Wynne-Davies' study of human L-P disease, only 17% of his 310 cases had a history of trauma (1). It is worthy of note that among such cases, trauma was unreported in children who developed the disease before the age of 3 years leading to a suspicion that it may have occurred but was not admitted. It is quite possible that puppy owners also are reluctant to admit to injuries in tiny puppies which might be charged to some level of carelessness. Preconceptions and misconceptions should not be allowed to influence learned fact…there are many of the former and all too few of the latter in this problem.
WHAT CHANGES OCCUR IN THE HIP IN LEGG-PERTHES?
Most investigators agree that the first change to occur in the hip joint is an ischemic episode…some event that shuts off the blood supply to the capital femoral epiphysis (Fig 4) If the blood supply is occluded the bone growth ceases, temporarily. At the same time the cartilage about this joint continues to grow because it is nourished by synovial (joint) fluid. This disparity between bone and cartilage growth creates a wider joint space and a smaller ossification center ... signs which can be detected on an x-ray plate.
After occlusion of the vessel(s) new capillaries will open to restore circulation but the bone growth will be uneven and the removal of the "dead" bone exceeds laying down of new bone. As a result, the area on the superior portion of the head becomes weak biomechanically. To this point in time, the disorder is subclinical..that is, the puppy (child) has no symptoms. The biomechanically weak femoral head may go on to heal and normal growth resumes. In this fortunate circumstance, the puppy will remain asymptomatic and have good to normal range of motion of the hip joint. Radiographic studies often reveal this early form of Legg-Perthes consequent to joint examination for other causes.
The symptomatic form of Legg-Perthes occurs when the weakened bone in the head of the femur fractures (Fig 5). Most opinion leans toward a fracture which can occur with normal vigorous activity rather than specific, identifiable injury. The operating factors are the degree of weakness in the bone and the extent of shearing forces applies across it. The occurrence of the fracture is the time when pain begins and, thus, is the onset of clinical Legg-Perthes.
The fracture rarely extends beyond its initial boundaries presumably because the resultant pain causes a decreased use of the extremity (limping) and, therefore, decrease of stresses on the femoral head. The fracture itself causes some circulatory occlusion so a second ischemic episode now occurs and it can involve a small part, or all, of the epiphysis. This second episode of avascularization results in loss of stability of the capital femoral epiphysis; growth of new capillaries is impeded and the femoral head is "softened" so-to-speak. The shape of the femoral head gradually is remodeled because bone in some areas will grow while other areas are being reabsorbed. The result is a femoral head that is asymmetric often giving rise to subluxation or extrusion of the joint and eventual physical deformity. Associated bone changes in the femur also occur which cause the affected limb to be shortened. Variations in muscle balance and strength cause a typical limp.
Onset of the Legg-Perthes occurs in puppies before the age of 1 year. The symptoms of Legg-Perthes are most frequently mild. The puppy will limp but will rarely cry-out or evidence severe pain. Owners will usually suspect a mild strain or sprain at first and may or may not confine the puppy to a crate. At any sign of a limp, a puppy should be confined to a crate for several days and if limping persists, orthopedic examination should be sought.
Abduction (movement of the limb away from the body) of the limb will cause discomfort or frank pain. While bilateral disease is known, most pups will have the disease in only one hip so the signs will be unilateral. Depending on the elapsed time since onset as determined by limping, the muscle bulk of the affected limb may be decreased (atrophy) and the leg may be shorter than the normal limb. Without treatment the puppy may cease to use the painful limb, causing a three-legged gait.
Radiography is the only means to confirm a diagnosis (Fig 6). The hip joint (particularly the femoral head) will be asymmetrical compared with the normal side…the head may be flattened or more severely deformed. The joint space will be wider and the head will show areas of different density on the film (moth-eaten appearance) (Fig 6). The Veterinarian also will make note of any changes in the joint socket (acetabulum) which may include spurs and osteoarthritic changes which add to joint pain. The latter problems, however, occur late in disease process.
To emphasize a critical point, any puppy with a limp should be confined to a crate immediately…size of the crate should permit comfort but not allow walking or jumping. The puppy should be carried outside several times a day only for elimination activities and should eat and sleep in the crate. An exercise pen is NOT satisfactory for such confinement. Crating the animal, while usually an effective way to treat sprains and the like, is highly unlikely to be effective in limiting or stopping the progression of Legg-Perthes disease. Naturally the owner cannot know what he is dealing with until the Vet makes a diagnosis…so immediate crating remains the initial treatment of choice.
Once the diagnosis of L-P is confirmed, the treatment of choice in Veterinary medicine is surgical excision of the head of the femur. While this may sound extreme, it is effective; it is a cure. Most persons will be unable to detect a limp in the dog after recovery from the procedure if the disease has been detected early. The surgeon will have several choices of operative approach, but correctly done, the result will be the same…a pain-free animal. The femur will gradually form a new joint (pseudarthrosis) with the pelvis; the extremity will be stable and, most importantly, usable. More expensive procedures, such as a total hip replacement are available, and these may be more functional, but in no case can or should the dog be used for show ... and not for breeding.
Postoperative care will include confinement in a crate while the restrictive dressings are in place. Carry the pup outside and place him down to eliminate but restrict walking. If the puppy will not leave the dressing alone, and Elizabethan collar may be applied. When wound healing is complete and the sutures removed gentle mobilization of the extremity should be done by the owner in addition to gradually permitting level-terrain walking. Such mobilization should include flexion/extension, and rotation only to the point where the puppy objects or reacts to pain. Avoid adduction (moving leg across the body) for the first several weeks or until the Vet approves. You do not want to stretch out the lateral tissues which the surgeon has reconstructed to stabilize the new joint. Gentle range of motion exercises may be done underwater if your pet is not afraid of the pool or a bathtub ... as it in the pool or tub with him and make a game of it. Gentle, non-friction massage will make him feel better and help him to become aware of his affected muscles ... again do not be rough in the early postoperative days. If you elect to do some massage, more your hands gently in the direction of the heart IF this does not cause discomfort by rubbing against the growth of the hair.
Ice packs can be used to reduce postoperative edema and so decrease the inevitable postop pain. NEVER apply ice directly to the animal but wrap cubes or chips in a towel of several thickness and hold the pup in your arms (while watch TV) replacing the pack every 20 minutes or so as you both can tolerate. The cold pack will have maximum effectiveness if wrapped around the extremity and not held on the hip in normal alignment (if a dressing including elastic bandages is in place the thickness of toweling can be decreased.)
Duration of walking should be increased gradually starting with the pup on a lead (do not pull!) and perhaps in an exercise pen. AS his tolerance builds up you must encourage curbs, gravel, sand, stairs and other uneven terrain walking to build up his strength and endurance. Now is the time to concentrate on mobilizing his joint in the motions of adduction, but abduction and adduction may never be as complete as in the normal limb. Do no ever move beyond an indication of pain by the pup. When in doubt as to what his range of motion should be, compare to the normal limb. Some decrease in joint range and some atrophy are to be expected but these should not impede the activity or full life of the animal.
Legg-Perthes disease is the result of multiple factors. A genetic predisposition, however weak, is combined with other determinants among which may be mild trauma, to set off the chain of events that lead to the clinical destruction of the capital femoral epiphysis. The several processes involved include mechanical collapse, asymmetric growth and disturbed endochondral ossification of the growth plate. A correctly treated puppy makes a marvelous pet but never a show or breeding animal.
1. Wynne-Davies R and Gormley J. The aetiology of Perthe's Disease. Genetics, epidemiological and growth factors in 310 Edinburgh and Glasgow patients.
2. Hall, DJ Genetic aspects of Perthes Disease. Clin. Orthop. 209; 100-114, 1978
3. Burwell RG, Dangerfield PH, Hall DJ, et al. Perthes Disease. An Anthropometric study revealing impaired and proportionate growth. J Bone Joint surg. 60B: 461-577, 1978
4. Ljumggren G Legg-Perthes disease in the dog. Acta Orthop Scand. Suppl. 95, 1967
5. Whittick WG, Canine Orthopedics Philadelphia Lea & Febiger 1974
6. Kemp HBS. Perthes Disease in Rabbits and Puppies. Clin Orthop. 209: 139-159, 1986
7. Kemp HBS Perthes Disease: The influence of intracapsular tamponade on the circulation in the hip joint of the dog. Clin Othop. 156: 105; 1981