抄録
Studies were made of 9 RA cases with stress fracture of the pelvic bone. Among the cases with fracture of os pubis or os ischii, several were observed with osteoporosis due to rheumatic disease, disuse and prolonged use of steroids. Increase in body weight (the upper half of the body was heavy or the lower limbs were thin) was seen in many cases who were also complicated by disorders of the sacro- iliac and hip joints, suggesting that stress tends to be applied to the symphysis pubis in front of the pelvic bone when walking in the flexion posture. The site of the fracture was mostly the symphysial surface of the corpus ossis pubis and ramus ossis iscii, which are the regions where the muscles and ligaments are attached.
The occurrence of fatigue fracture and dislocation of the bone are ascribable to muscular action. The loading of stress being concentrated in the forward direction at the corpus ossis pubis and symphysis pubis causes compression fracture. If the symphysis pubis cannot bear the load, torsion is repeatedly applied to the ramus ossis ischii and ramus ossis pubis, causing bending fracture in these regions.
Thus it was considered that fatigue fracture of the pelvic bone is caused by combined factors such as dynamic elements, fragility of bone accompanying RA and abnormality due to RA lesions in the lower limbs.
