Ultrasonographic evaluation of patellar tracking in children.

Patellar positions with the knee in extension and in 10 degrees and 20 degrees flexion were measured by ultrasonography in both knees of 20 children with patellar dislocation and in both knees of 30 healthy children for controls. Ultrasonography proved to be applicable to measuring the distance between the most anterior point of lateral femoral condyle and patellar apex, the sulcus angle and the vertical position of the patella. Compared with normal knees, the sulcus angle was wider and the patellar position more lateral and cranial in both the dislocated and asymptomatic knees of the patients. These results suggest that false tracking of the patella in early flexion is a predisposing factor to patellar dislocation.

Bone formation after distraction osteotomy of the radius in sheep.

Gradual distraction by external fixation was performed one week after osteotomy of the radius in 12 sheep. Bone regeneration in the distraction area was studied by light and electron microscopy. One week after starting the distraction the gap was composed of hematopoietic cells and fibroblasts. The collagen production had already started and it continued actively throughout the distraction period. The collagen produced by the fibroblasts in the central interzone of the gap was organized according to the direction of the distraction. The osteoblasts were lined up along the collagen bundles and osteoid formation was most active around the capillaries. Mineralization started two weeks after the beginning of the distraction. After cessation of the distraction, separate groups of cartilaginous cells were found in some specimens among the newly formed bone. Our findings suggest that osteogenesis as a result of gradual distraction occurs through the whole distraction area with preceding formation of organized collagen matrix. The bone structure in the distracted segment represents an organized lamellar structure at an early stage of the osteogenesis.