This is a relatively simple case. The lateral and AP projection of the knee demonstrate minor degenerative changes of the knee including the patellofemoral joint. However, there is an abnormality of the distal femur. The femur demonstrates patchy diffuse sclerosis. This extends extensively beyond the articular margin of the joint and is, therefore, not related to a degenerative process. The patchy appearances may suggest an infiltrative disorder such a metastasis or a primary osteogenic lesion. However, there are other features here that suggest an alternative diagnosis.
The distal femur demonstrates thickening and coarsening of the medullary trabeculae. The cortex of the distal femur is also considerably thickened compared to the cortex of the femur. Further one can appreciate that the femur size is subtly enlarged compared to the tibia. Finally, the entirety of the femur is involved extending to involve all of the femoral condyles to the articular surface.
These are classical appearances of Paget’s disease. Paget’s disease typically involves the entirety of a single bone extending from one articular surface to the other side of the bone. The typical appearances seen here those of coarsening of the trabeculae, cortical thickening, sclerosis and osseous enlargement. Bowing may then develop in the long bones. This is typically lateral in the femur but anterior in the tibia. Premature degenerative change is also a feature in long bones.
Paget’s disease most typically involves the pelvis although involvement of other sites including the skull, proximal long bones and vertebrae is also common. Both poly-ostotic and mono-ostotic variations can occur. The mixed osteosclerotic and osteolytic phase observed here is preceeded in some patients by a pure osteolytic phase that is often not clinically detected. This may in the long bones be associated with an advancing margin often likened to a “blade of grass” or the “candle flame sign”. A later fully sclerotic osteoblastic phase may occur.
Although there is often extensive sclerosis the serum calcium and phosphate levels are normal with increase in serum Alkaline Phosphatase or urinary hydroxyproline the only consistent biochemical findings. Clinically approximately 75% of patients are incidentally detected and asymptomatic, although local pain and even symptoms of increased heat sensation can occur with long-bone involvement. Long term the principle concerns of long bone involvement are deformity, fractures, and in approximately 1% of patients, osteosarcoma transformation. Treatment is with bisphosphonate therapy.