Physeal dysplasia with slipped capital femoral epiphysis in a cat

Abstract

A 14-month-old, intact male cat presented with acute onset, severe right hind limb lameness. Pelvic radiographs, excision of the femoral head, and histopathologic examination resulted in a diagnosis of physeal dysplasia with slipped capital femoral epiphysis. The cat rapidly regained use of the affected limb.

A 14-month-old, intact male domestic shorthair with no history of trauma presented (day 1) with acute onset, nonweight-bearing lameness of the right hind limb of 9 d duration. The 4.4-kg cat, which was kept indoors, had not been vaccinated. His diet consisted of commercial cat food. Pain was elicited upon palpation of the hip area. Rectal temperature was not taken, and there were no other abnormal findings.

On the basis of the history and physical examination, a tentative diagnosis of traumatic femoral fracture was made. Differential diagnoses included hip dysplasia, osteomyelitis, neoplasia, and aseptic necrosis of the femoral head. The cat was admitted for radiographic examination. Lateral and ventrodorsal pelvic radiographs showed lysis affecting the right femoral metaphysis, with a slight lateral displacement of the epiphysis. There was an irregular, complete radiolucent line across the metaphysis. The femoral epiphysis and diaphysis were intact. A closed physis was present on the left. Surgical excision of the right femoral head was scheduled for day 3.

Preoperative serum biochemical analysis and complete blood cell count values were within normal values, and tests for feline leukemia virus and feline immunodeficiency virus were negative. A 25-μg fentanyl patch (Abbott Laboratories, Toronto, Ontario), was applied the evening before surgery as a control for postoperative pain. The coxofemoral joint was approached surgically through a craniolateral skin incision. The biceps femoris muscle was retracted caudally and the tensor fascia lata muscle was retracted cranially. The origin of the vastus lateralis muscle was incised and then reflected ventrally to expose the joint capsule, which was then incised. Bone resorption and fibrous tissue proliferation were evident at the fracture site. The epiphysis of the femur was attached at its lateral margin by the perichondrium. The epiphysis was excised and the remainder of the femoral neck was removed by using bone ronguers. The joint capsule, muscles, subcutaneous tissue, and skin were closed. Castration was then performed.

The femoral epiphysis and attached section of metaphysis were submitted in 10% buffered formalin for histopathological examination. Postoperative lateral and ventrodorsal pelvic radiographs confirmed adequate removal of the femoral metaphysis. The cat was treated with a nonsteroidal anti-inflammatory (Ketoprofen; Merial, Baie d'Urfé, Quebec), 2 mg/kg bodyweight (BW), PO, q24h for 4 d, and with an antibiotic, cephalothin (Keflin; Novopharm, Toronto, Ontario), 96 mg, IM, q24h for 2 d.

On day 4, the cat appeared upset, was pained, and avoided use of the right hind limb. By day 5, he was comfortable and eating. By day 6, he was bright and weight bearing with mild discomfort. The cat was released from the clinic on unrestricted exercise, with owner instructions to administer clindamycin (Antirobe Aquadrops; Janssen Animal Health, Toronto, Ontario), 11 mg/kg BW, PO, q24h for 10 d, and to return to the clinic on day 8 for removal of the fentanyl patch.

By day 20, when sutures were removed, the cat was using the right hind limb well, but walked with a limp. Pain was elicited upon manipulation of the right hip. Radiographs revealed a small amount of soft tissue swelling. The owners reported continued improvement in the cat's condition at 6, 9, and 12 wk postsurgery.

The histopathological diagnosis was physeal dysplasia with slipped capital femoral epiphysis (SCFE), with remodelling changes and evidence of healing of previous necrosis within the femoral head. According to the pathologist's report, in some regions, the bony trabecula of the epiphysis had been replaced with osteogenic tissue. Small fragments of dead bone were surrounded by either fibrous connective tissue or polygonal cells, suggestive of osteoblastic cells. The entire epiphysis was surrounded by fibrous connective tissue. In the small area of physeal cartilage included in the section, chondrocyte columns were irregularly oriented and groups of chondrocytes were arranged in spherical clusters. The synovial membrane was thickened with marked hyperplasia of the synoviocytes, which in places was up to 4 or 5 cells thick. Observation of irregular clusters of chondrocytes separated by abundant matrix on both the epiphyseal and the metaphyseal side of the physeal cartilage cleavage site is characteristic of SCFE (2). In contrast, with traumatic injury, chondrocytes retain normal linear arrangement on both sides of the fracture site (2).

The cat's prognosis for return to adequate, painless function is excellent, as postoperative complications of femoral head and neck excision are rare (1). Craig (2) reported that 11 out of 13 cats diagnosed with physeal dysplasia and SCFE had uneventful recoveries and good limb function after femoral head and neck excision. Queen et al (6) observed that most cats used the affected limb to some extent within 10 d of surgery, and were completely sound by 3 mo. Physeal dysplasia with SCFE is a recently described disease in cats (2,4,6). Separation of the femoral capital epiphysis is usually associated with traumatic injury in most species, although Craig (2) and Forrest et al (4) describe 23 cases in which predominantly indoor cats with no history of major trauma developed SCFE. Most (85%) were males, and 90% of them were neutered; 90% of the cats were overweight; 50% were domestic shorthairs, and 23% were Siamese (2,4). The duration of clinical signs at presentation averaged 20.8 d (4).The cats ranged in age from 4.5 to 24 mo, with an average age of 16.3 mo (2,4), and 50% to 90% of them were bilaterally affected (4). As there is up to 90% progression to involvement of the opposite femoral epiphysis, affected cats may become lame on the opposite limb postsurgically, requiring a second femoral head and neck excision.

Few studies of physeal dysplasia with SCFE in cats have been reported in the veterinary literature, and they do not include large numbers of cases. The pathogenesis of this condition is, therefore, not well understood, although it is thought to be a local cartilage disorder. Lesion development requires an open physis. Since growth plates close at 7 to 9 mo in normal, healthy, intact cats, affected animals have a delayed growth plate closure (2). The cartilaginous lesion may represent preexisting dyschondroplasia of the physis or late stage repair after a separation of the capital femoral epiphysis (6). Histopathological examination of bone excised from affected cats suggests that physeal dysplasia results in abnormal cartilage and persistence of an open, disorganized growth plate that cannot resist the shear forces associated with normal activity (2). Genetics, nutrition, obesity, endocrine imbalances, and other factors may contribute to the development of SCFE (2). Similar lesions acquired atraumatically have been reported in humans, pigs, and Shetland sheepdogs, suggesting that these species may have an analogous physeal dysplasia (2).

Femoral neck fractures in cats are often assumed to be the result of traumatic injury, although the incidents are seldom witnessed by owners (6). Physeal dysplasia with SCFE should be considered a differential diagnosis in such cases, particularly if the animal fits the demographics for this condition.