Occult hip and pelvic fractures and accompanying muscle injuries around the hip

Method We investigated the incidence of occult hip and pelvic fractures and associated muscle injuries around the hip. Patients A total of 113 patients aged 60-102 years with suspected hip fracture but negative plain radiographs underwent further examination by magnetic resonance imaging (MRI) within 2 days after an X-ray examination. Coronal and axial T1 and T2 or short tau inversion recovery sequences of MRI of the hip including the sacrum were obtained. Results One hundred and two cases (90.2%) had bone or soft-tissue abnormalities and 83 cases (73.5%) had fractures of the hip and/or pelvis. The frequency of hip fracture and pelvic fracture was almost the same. More than half of the patients among those with pelvic fractures sustained occult sacral fractures; therefore, it was important to determine if a sacral fracture was involved when occult hip fracture was suspected. Muscles located at the lateral aspect of the hip, such as gluteus maximus, gluteus medius, gluteus minimus and quadratus femoris, were frequently injured in cases with intertrochanteric and greater trochanter fracture, suggesting that direct impact may be associated with fractures of the trochanteric region. However, hip rotator and adductor muscles such as obturator internus, obturator externus and adductor brevis were commonly injured in cases with pelvic fracture, indicating indirect force mediated by these muscles may be associated with pelvic fracture. Conclusion Occult hip and pelvic fractures were almost equally seen among 113 cases with suspected hip fracture but were negative on plain radiography. Different patterns of associated muscle injuries in cases of occult hip fracture and pelvic fracture suggest that the mechanism of hip fracture and pelvic fracture is possibly different.