Legg-Calvé-Perthes disease (LCPD) is a childhood hip disorder that results in infarction of the bony epiphysis of the femoral head. LCPD represents idiopathic avascular necrosis of the femoral head.
It usually affects children aged 4-8 years. The disorder is more frequent in boys than in girls 5:1 .
Bilateral abnormalities are detected in about 10 – 20 % of cases. When both hips are involved, they are usually affected successively, not simultaneously. Bilateral symmetric fragmentation of the capital femoral epiphysis should suggest the presence of other disease, such as hypothyroidism or sickle cell anemia.
The disease process is characterized by loss of circulation to the head of the femur (the ball of the hip) in a growing child resulting in avascular necrosis (death of bone cells in the head of the femur). This is typically followed by revascularization over a period of 18 to 24 months. During the period of revascularization, the bone is soft and liable to fracture under pressure, causing collapse of the head of the femur. Over time, the head of the femur heals and remodels in the collapsed position, resulting in a nonspherical shape. This leads to stiffness and pain.
The principle clinical signs are limping, pain and limitation of joint motion.
Radiographic abnormalities:
- Soft tissue swelling on the lateral side of the articulation and increased Kohler's teardrop distance (Waldenstrom's sign). Capsular bulging with displacement of the capsular fat pad relates to the accumulation of the intraarticular fluid.
- Smallness of the femoral ossification nucleus.
- Lateral displacement of the femoral ossification nucleus.
- Fissuring and fracture of the femoral ossific nucleus. This sign may be detected only on radiographs obtained in frog leg position.
- Flattening and sclerosis of the femoral ossific nucleus predominantly in the antero lateral superior segment of the femoral head. The frog leg position is optimal for visualizing the degree of bone flattening.
- Intraepiphyseal gas.
- Metaphyseal cysts.
- Widening and shortening of the femoral neck.
Early radiographic changes useful to indicate a femoral epiphysis at risk for collapse include
1. Gage sign: a small, osteoporotic segment that forms a transradiant V on the lateral side of the epiphysis.
2. Calcification lateral to the epiphysis – reflecting the presence of extruded cartilage.
3. Lateral subluxation of the femoral head.
4. A transverse physeal line.
Course of the disease: Finally the femoral head will remodel into the "mushroom deformity."
The signs of the mushroom deformity of the femoral head include coxa magna (enlargement of the femoral head) and coxa plana (flattening of the femoral head). Other associated radiographic features to look for include remodeling of the acetabulum, coxa vara (femoral neck angle of less than 120 degrees) and the sagging rope sign (representing the edge of the flattened femoral head).
Several staging schema are used to determine severity of disease and prognosis; these include the Catterall, Salter-Thomson, and Herring systems.
The Catterall classification is based on radiographic appearances and specifies 4 groups during the period of greatest bone loss.
Catterall staging is as follows:
- Stage I - Histologic and clinical diagnosis without radiographic findings
- Stage II - Sclerosis with or without cystic changes with preservation of the contour and surface of femoral head
- Stage III - Loss of structural integrity of the femoral head
- Stage IV - Loss of structural integrity of the acetabulum in addition
The Salter-Thomson classification simplifies the Catterall classifications by reducing the groups to 2. The first, called group A includes Catterall groups I and II and indicates that less than 50% of the head is involved. The second, called group B, includes Catterall groups III and IV and is used when more than 50% of the head is involved. Both classifications share the view that if less than 50% of the ball is involved, the prognosis is better, whereas when more than 50% is involved, the prognosis is potentially poor.
The Herring classification addresses the integrity of the lateral pillar of the head. In Lateral Pillar group A, there is no loss of height in the lateral one third of the head and little density change. In Lateral Pillar group B, there is a lucency and loss of height of less than 50% of the lateral height. Sometimes, the head is beginning to extrude the socket. In Lateral Pillar group C, there is more than 50% loss of lateral height.