Legg-Calvé-Perthes disease

What it is

Aseptic (avascular) necrosis of the femoral head and neck during growth. For reasons that are not fully understood the blood supply to the femoral epiphysis is interrupted, the subchondral bone dies and, when the body tries to revascularise and repair the area, the softened bone collapses under load. The head loses its spherical shape, the cartilage cracks and osteoarthritis develops. A hereditary component has been proposed (an autosomal recessive pattern has been described in the Manchester terrier), and the vascular anatomy of the immature femoral neck probably plays a part: the epiphyseal vessels cross the joint capsule and are vulnerable to compression.

Who it affects

Small and toy breeds: Yorkshire terrier, West Highland white terrier, toy and miniature poodle, Manchester terrier, Cairn terrier, pug, miniature pinscher. The typical age at presentation is between 4 and 11 months. It is usually unilateral; a minority of cases are bilateral. There is no clear sex predisposition.

Anatomy involved

• Femoral head (caput ossis femoris): flattens, deforms and may fragment; the articular cartilage separates from the necrotic bone.
• Femoral neck (collum ossis femoris): shortens and thickens with remodelling.
• Acetabulum: normally well formed, which distinguishes this disease from hip dysplasia, although it develops secondary osteoarthritis.

Clinical signs

Progressive lameness of one pelvic limb that starts insidiously and within weeks may progress to non-weight-bearing. Pain on extension and abduction of the hip, crepitus and marked atrophy of the gluteal and thigh muscles. Some puppies lick the area or become irritable.

Diagnosis

Ventrodorsal pelvic radiograph, supplemented with the "frog-leg" view. Early changes are subtle: foci of reduced density in the epiphysis and widening of the joint space. Later, "moth-eaten" lytic areas, flattening and irregularity of the head, collapse and fragmentation, and thickening of the neck appear. Computed tomography detects early lesions. It must be distinguished from capital physeal fracture and from hip dysplasia, which is rare in toy breeds.

Treatment

Conservative management (rest, analgesia) rarely achieves acceptable function, because the deformity progresses. The treatment of choice is femoral head and neck excision arthroplasty (FHO): in a small dog the resulting fibrous pseudoarthrosis allows an almost normal gait to be recovered, especially with early physiotherapy. In selected cases a total hip replacement may be considered. The prognosis after surgery is good to excellent.