Osteonecrosis of the femoral head of young, small breed dogs (commonly known as Legg-Calve-Perthes [LCP] disease) was first described in veterinary literature by Tutt in 1935:(12) he described the disease, as did Waldenstrom (1909) in humans,(13) as tuberculosis of the hip. In 1910, Legg, Calve, and Perthes independently described a condition of the hip in children, which bears their name.(3,7,10) It is interesting to note that although all three described the clinical entity, only Legg stated the most accepted pathogenesis, which he thought to be impairment of the blood supply to the femoral epiphysis. Calve thought that the condition was due to rickets, and Perthes thought that it related to a degenerative arthritis, probably of an infective nature. Spicer (1936), Schnelle (1937), and Moltzen-Nielsen (1938) described the condition, using some form of the eponym of LCP disease, in the veterinary literature.(9) Common synonyms for this condition are avascular necrosis of the femoral neck, aseptic necrosis, osteonecrosis, coxa plana, osteochondritis deformans juvenilis, and osteochondrosis.
LCP disease is an osteonecrosis of the femoral head in small breed dogs, usually those weighing less than 12 kg. There seems to be no sex predilection in the dog as contrasted to humans, in whom an 80% male incidence of the disease is evident. As in children, however, the condition is usually unilateral, with only about 10% to 15% incidence of bilateral disease. The age of onset varies between 4 months and 12 months, with a peak incidence at about 7 months.
The etiology of the condition is unknown. The pathologic features are typical of avascular necrosis of bone. Experimental studies producing avascular necrosis have been performed, but these studies do not duplicate the necrosis that is seen clinically. Legg, in his original thesis, thought that the vascular problem was due to trauma, but Trueta, in describing his "epiphyseal anemia" emphasizes the precarious blood supply of the femoral epiphysis of children and the reinforcing of this blood supply as the child grows older.(11) The blood supply to the femoral head of the immature dog seems more complete, as suggested by Bassett and co-workers.(1) This multiple origin of the vascular network of the femoral head in the dog allows room for additional hypotheses (Fig. 82-1). Ljunggren (1967) suggested a possible endocrine etiology and showed the osteonecrosis that occurs with a high dosage of steroids (estrogens and/or testosterone).(9) Her hypothesis was predicated on the idea that the morphologic picture of LCP disease in the dog is a manifestation of precocious sexual maturity. Although the experimental evidence in this study is supportive of this idea, no reasons are advanced to explain the unilateral nature of the condition or the low incidence in a breed population that is characterized by precocious sexual maturity. The pathology of avascular necrosis followed by revascularization and bony remodeling of the femoral head in the dog certainly suggests a vascular etiology even though the cause of the condition is not completely understood.(4)
|FIG. 82-1 The normal vascular pattern of a young dog's proximal femur (left) is compared with one in which only the inferior reticular vessels are intact (right). (Courtesy of Dr. W.H. Riser)|
The animal is usually presented with a limp. Physical examination shows some pain on extension of the hip joint, particularly with internal rotation. The dog will also evidence pain on forced abduction of the hip joint. Advanced signs include muscle contracture and/or apparent shortening of the leg on the affected side associated with collapse of the femoral head.
The first radiographic signs are those of increased joint space. Radiographic signs in the femoral head itself are evident only after vascular resorption of the necrotic bone has begun (Fig. 82-2). It is at this time that danger from collapse of the femoral head begins. If left to follow its normal course, collapse of the femoral head with distortion of the coxofemoral joint will occur, followed by fragmentation of the femoral head (Fig. 82-3). These changes in structure result in significant loss of function with secondary muscle atrophy.(2,5)
|FIG. 82-2 Radiograph shows vascular resorption of the femoral head in the area outlined by the vascular supply in Figure 82-1. right|
|FIG. 82-3 (A) Cranial-caudal radiograph demonstrates femoral head collapse in a dog with Legg-Calve-Perthes Disease. (B.) The hip 14 months following femoral head and neck resection. (Courtesy of Dr. R.B. Hohn)|
Conservative therapy has in the past consisted of a general resting of the limb without casts or bandages. Surgical treatment by removal of the femoral head and neck has been advocated, and reported results indicate that surgery is the preferred treatment.(6,8,9)
The only criterion on which to base the choice of treatment modality is the radiographic picture of the affected limb. Clinical signs are considered secondarily.
If the femoral head is round, the joint space parallel, and the femoral head and acetabulum congruent, strict immobilization of the patient in a small space (cage) will usually result in a resolution of the radiographic and clinical problem. During the enforced rest, the animal is allowed out of the cage only to maintain its toilet training. The animal is carried to and from the cage and kept on a leash during evacuation (Fig. 82-4).
Monthly radiographs are taken to follow the progression of the disease. Immobilization of the animal is continued until there is complete resolution of the radiolucent areas. If collapse of the femoral head occurs during the confinement, surgical treatment is performed.
Strict adherence to this form of treatment yields a dog with nearly normal radiographic appearance of its femoral head and complete return of pain-free motion and a normal gait. It takes 4 to 6 months before the femoral head heals sufficiently to permit unrestricted weight bearing. Any compromise to complete immobilization will result in the collapse of the femoral head and a poor outcome.
|FIG. 82-4 (A) Ventral dorsal radiograph of the hips of a 6-month-old, long-haired dachshund. Note the lytic lesion in the right femoral head, which represents Legg-Calve Perthes disease. The dog was treated with cage confinement. (B.) Remodeling 2 months later. (C) The healed, remodeled end result of conservative management 6 months later. The dog was not lame.|
An animal that is presented with collapse of the femoral head with incongruence of the coxofemoral joint and an uneven joint space with pain is a candidate for femoral head and neck resection (see Fig. 82-3). if left untreated, the animal will undergo extensive muscle atrophy with concomitant disability before there is some partial improvement following revascularization of the collapsed head. This animal will develop osteoarthritis and may become severely crippled.
Following surgery, exercise will help return the animal to reasonable function. Gradual improvement following resection of the femoral head and neck can continue for up to one year. The primary function of the surgery is the relief of pain, but the small size of these patients usually ensures adequate function.
1. Bassett FH, Wilson JW, Allen BW et al: Normal vascular anatomy of the head of the femur in puppies with emphasis on the inferior retinacular vessels. J Bone Joint Surg 51A: 1139, 1968
2. Caffey J: The early roentgenographic changes in essential coxa plana: The significance in pathogenesis. Am J Roentgenol Radium Ther Nucl Med 103:620, 1968
3. Calve J: Sur une forme particuliere de pseudocoxalgie greffee sur des deformations characteristiques de l'extremite superieure du femur. Rev Surg 42:54, 1910
4. Hulth A, Norberg 1, Olsson S-E: Coxa plana in the dog. J Bone Joint Surg 44A:918, 1962
5. Lee R: A study of the radiographic and histologic changes occurring in L-C-P disease in the dog. J Small Anim Prac 11:621, 1970
6. Lee R. Fry PD: Some observations on the occurrence of L-C-P disease (coxa plana) in the dog and an evaluation of excision arthroplasty as a method of treatment. J Small Anim Pract 10:309, 1969
7. Legg A: An obscure affection of the hip joint. Boston Med Surg J 162:202, 1910
8. Ljunggren G: A comparative study of conservative and surgical treatment of L-P disease in the dog. Anim Hosp 2:6, 1966
9. Ljunggren G: Legg-Perthes disease in the dog. Acta Orthop Scand (Suppl) 95: 1967
10. Perthes G: Uber arthritis deformans juvenilis. Dtsch Z Chir 101:779, 1910
11. Trueta: Studies of the Development and Decay of the Human Frame. Philadelphia, WB Saunders, 1968
12. Tutt JFD: Tuberculosis of the hip joint in a cairn terrier. Vet Rec 47:428, 1935
13. Waldenstrom H: Der oobere Tuberculose Collumherd. Orthop Chir 24:487, 1909