Deformation and vascular occlusion of the growing rat femoral head induced by mechanical stress.

To investigate the effects of mechanical stress on the extent of deformation and decrease of the blood supply to the femoral head in the growing rat, we conducted a histological and microangiographic study, using a custom-made hip-joint loading device. Application of a 1-kg to 3-kg load to the hip joint caused compression not only of the articular cartilage but also of the growth plate of the femoral head. These changes were particularly prominent in the lateral portion of the femoral head. The compression also caused complete occlusion of the lateral epiphyseal arteries, representing the blood supply to the femoral head, at the point of penetration into the epiphyseal cartilage. Our results indicate that the sum of forces during mechanical load application to the hip joint in growing rats acts to deform the cartilage of the lateral side of the femoral head. Our results also indicate the presence of a mechanically weak point in the femoral head which may lead to occlusion of the lateral epiphyseal arteries.