Fatigue stress injuries of the pelvic bones and proximal femur: evaluation with MR imaging.

The purpose of this study was to determine the prevalence and the distribution as well as male/female differences in patients with hip or pelvic pain based on MRI results. Three hundred forty consecutive conscripts (45 women, 295 men; age range 18-29 years; mean age 20.7 years) suffering from stress-related hip, buttock or groin pain took part in the study. All 340 patients underwent MR imaging. Radiographic data were available for 215 patients. Two radiologists interpreted the images by consensus. In MRI 174 stress injuries were diagnosed in 137 patients (32 women, 105 men). The incidence of bone stress injuries in women was significantly higher than that in men ( p<0.0001). One hundred five of the injuries (60%) were related to the proximal femur, 70 (67%) to the neck, 34 (32%) to the proximal shaft, and one (1%) to the head. Sixty-nine of the 174 stress injuries (40%) concerned the pelvic bones: sacrum 28 (41%); inferior pubic ramus 34 (49%); superior pubic ramus 3 (4%); iliac bone 3 (4%); and acetabulum 1 (1%). In 31 of the 174 cases (18%) symptoms were contralateral to MR findings. Thirty-three of the 137 patients (24%) had multiple bone stress injuries, 29 had two bone stress injuries and 4 patients had three. The sensitivity of radiography was 37%, specificity 79%, accuracy 60%, positive predictive value 59% and negative predictive value 61%. The kappa value for agreement between radiography and MRI was poor (0.17, p=0.0008). Patients suffering from stress-related hip pain MRI revealed bone stress injuries in 40%; of these, 60% were located in the proximal femur and 40% in the pelvic bones. For accurate diagnosis of bone stress injuries, and to ensure appropriate treatment, the entire pelvis and both proximal femurs should be studied simultaneously by means of MRI.