Bone density changes of the femoral head in transient synovitis of the hip were investigated by analyzing the PACS pixel value.

Seventy seven patients diagnosed as unilateral transient synovitis of the hip were investigated. Conventional plain anteroposterior (AP) and frog-leg lateral projection films of the hip were studied for pixel value measurements in PACS. The pixel values of the center of femur head, the periphery of femur head, the femur neck, and the intertrochanter of proximal femur were measured.

The pixel value ratios for healthy versus involved sites at the center of the femoral head, at periphery of the femur head and at the femur neck were 1:0.967, 1:0.967 and 1:0.967 on AP view, and 1:0.961, 1:0.955 and 1:0.965 on frog-leg lateral view. The relative pixelvalues were maximally decreased around 2 weeks after symptom onset. After 2 months pixel values of the involved side were nearly normal.

There was a significant decrease in the pixel value of the involved side, which may have been due to disuse atrophy. Also, the pixel value seemed to be useful for quantifying changes of the bone density in transient synovitis of the hip.