Imaging of the hip

Full text: Standard radiographs represent the basic tool of hip joint imaging. For detailed analysis of abnormalities related to bone marrow, articular cartilage, labrum and periarticular soft tissues, MRI has become the method of choice. MR arthrography is superior to standard MRI with regard to depicting the intra-articular abnormalities. CT is supporting plain radiographs for accurate depiction of subtle bone details. Ultrasound is commonly used in postoperative hematoma, bursitis, initial diagnosis of cysts and solid soft tissue tumors as well as for image guided injections and biopsies. Bone scintigraphy is suitable for the mapping of multifocal disease, such as osseous metastatic deposits. PET and PET/CT may be able to differentiate malignant neoplasm and infection from other abnormalities. A common disorder often requested for evaluation, is osteoarthritis. MRI is able to depict early degenerative changes which are occult on plain radiographs. CT- or MR arthrography provide a better evaluation of these changes but should only be performed in cases in which conservative surgery is considered to offer a significant clinical improvement for the patient. These cases include cam type femoroacetabular impingement and traumatic chondrolysis. MRI is an imaging technique that allows direct visualization of the bone marrow. Marrow disorders of the hip may induce a variety of imaging findings and frequently are not detected by conventional radiographic techniques until they have reached an advanced clinical stage. The excellent spatial and contrast resolution provided by MRI facilitates early detection and evaluation of various disorders allowing thus prompt treatment. Imaging findings may alter or guide the correct treatment. In addition, the association of marrow changes and pain such as in osteonecrosis and osteoarthritis is clinically relevant. For imaging the bone marrow, we use a combination of pulse sequences, including T1-w spin echo, PD/T2-w turbo spin echo with fat suppression and turboshort T1 inversion recovery. In selected cases, contrast enhanced T1-w spin echo with fat suppression is applied. Radiological interpretation of the marrow space requires an understanding of normal maturation and recognition that red and yellow marrow coexist with variable amounts depending upon the age and location. With MRI, this variability yields normal patterns ranging from very uniform and homogeneous signal intensity to patchy and heterogeneous signal intensity. Signal changes also depend on the pulse sequence applied. The marrow reflects the health of the patient and may herald developing anemia with marrow reconversion from inactive to active. Clinical correlation will contribute to narrow the differential diagnosis. Bone tumors may require additional imaging with CT in order to explore the pattern of matrix calcification and/or guide a diagnostic biopsy