What is Legg-Perthes Disease?
Legg-Perthes disease is a non-inflammatory, non-infective death of the cells of the femoral head that occurs in young dogs before the growth plate of the femoral head closes.
How and Why Does it Occur?
The disease results in the collapse of the femoral neck due to an interruption of blood flow. The reason for loss of blood flow is unknown but it has been suggested that hormonal influence, hereditary factors, anatomic conformation, intracapsular pressure and/or lack of blood flow to the femoral head may be responsible. The blood supply to the femoral head is derived solely from blood vessels that course along the surface of the femoral neck, cross the growth plate and then penetrate the bone to supply nutrients to the femoral head. Inflammation of the joint capsule or sustained abnormal limb position may increase the pressure inside the joint enough to collapse the fragile veins and inhibit blood flow. A recessive gene has been suggested as a genetic cause for the development of non-infective necrosis of the femoral head.
The body repairs the area via re-vascularisation once the femoral head cells die. Unfortunately, the bone substance has been weakened mechanically to the extent that normal weight bearing forces can cause collapse and fragmentation of the femoral head. When this occurs there is an abnormal fit of the femoral head and hip socket which results in the occurrence of degenerative joint disease (i.e. arthritis). The arthritis and fragmentation of femoral head and/or neck in turn cause pain and subsequent lameness.
How Can the Condition be Diagnosed?
The disease is diagnosed in young small breed dogs between the ages of 3 and 13 months with the peak incidence being between 6 and 7 months. Affected dogs usually present with a slow onset of weight bearing lameness that worsens over a 6 to 8 week period, and may even progress to non-weight bearing lameness. In some cases where there is a sudden collapse of the femoral head the dog will present with an acute onset of lameness.
Reduced range of movement, grinding feeling, muscle withering and pain are usually noticed as the hip is flexed and extended. The Legg-Perthes disease can be confirmed by X-raying the hip area. Radiographs show a deformed femoral head, shortening and/or lysis of the femoral neck and areas of reduced bone density within the femoral head.
What are the Treatments for Legg-Perthes Disease?
Definitive diagnosis is usually made after the femoral head has collapsed and fragmented and degenerative joint disease is present. The condition is not painful during the early stage in most cases. Conservative treatment with anti-inflammatories and non-weight bearing exercise such as swimming is usually unsuccessful at this stage and surgery to remove the affected femoral head and neck is required to relieve the lameness.
In rare cases when diagnosis is made before the femoral head has collapsed, limited weight bearing on the affected leg during the re-vascularisation period may be successful.
It is important that the dog is encouraged to use the limb immediately after the operation if surgical removal of affected femoral head and neck is the 'repair' process. The dog is placed on anti-inflammatories with passive flexion and extension of the hip to be conducted twice daily.
How Successful is Surgery?
The chance of normal limb use after removal of the femoral head and neck is good due to the small size of the affected dog. However, slight intermittent lameness may occur during damp weather or after heavy exercise.