CT is used to further characterize a bony detail of the hip not available on plain radiographs by providing cross-sectional information. CT of the hip should be done primarily in the setting of trauma or in suspicion to the neoplasm of the proximal femur or acetabulum. Occasionally, it is used to evaluate developmental hip dysplasia, to detect the small particle disease, and to evaluate for nonunion [12]. Multislice helical CT has markedly improved our ability to rapidly acquire high-resolution images with multiplanar 2D or 3D reconstruction with the benefits of a lower radiation dose than conventional CT, to improve resolution and to help us reduce the exam time. 3D CT reconstruction shows us a three-dimensional view of the acetabulum and femoral head and neck in FAI syndromes. The 3D CT helps us to clarify where exactly the cam or pincer lesion or other different abnormalities are situated, and therefore, it is very helpful in preoperative planning (Figs. 33.3, 33.4, and 33.5). In our institution, 3D CT is performed in every patient before and also after arthroscopic management of the FAI syndrome to clarify whether the resection of the cam or pincer lesion has been sufficient.

In the setting of trauma, CT of the hip is used primarily to better characterize a fracture or fracture dislocation and to aid in the detection of articular surface fractures and intra-articular loose fragments [1]. CT can also yield information used in predicting hip instability in fractures of the posterior wall of the acetabulum.

CT offers a tool for preoperative measurement and planning for patients undergoing hip arthroplasty and can also be helpful in detecting and determining the extent of osteolysis around the hip prosthesis [13]. But in this case, a high artifact-free protocol is necessary.

CT can be used to help characterize the nature of the tumor matrix and demonstrate cortical thinning or destruction, in cases of neoplasm [14].

CT arthrography of the hip is an excellent alternative to MR arthrography in patients with presence of loose metallic implants, presence of cardiostimulator, or with any other contraindications to MRI. CT arthrography can elucidate intra-articular abnormalities due to leakage of contrast into sites of labral, chondral, or ligamentous injury and can demonstrate loose bodies. Intra-articular injection before CT arthrography is preferably carried out using a combination of iodinated contrast with bupivacaine. In case of pain relief after local anesthetic application, it can help us to distinguish intra-articular from extra-articular sources of the hip pain [14].

Ultrasound is a complementary diagnostics method to MRI in the evaluation of hip pain. Ultrasound is suitable especially for the evaluation of snapping hip syndrome and image-guided intervention [15, 16]. This method has many advantages over other imaging methods: It is noninvasive; it lacks ionizing radiation, allows concomitant evaluation of the contralateral hip, allows dynamic examination of the tendons and muscles, and can recognize pathologies of the tendons and soft tissue; and it is an inexpensive and quickly performed method and can be used as a guide for therapeutic injections and aspirations [17]. Ultrasound may provide a useful tool for early diagnosis of the cam-type FAI in daily practice [18].

Ultrasound is an excellent noninvasive tool for the diagnosis of different types of snapping hip syndrome in patients in case the snapping phenomenon may occur during a movement of the hip in the course of the examination [15].

Despite these advantages, ultrasound does not provide anatomic overview and demonstration of the bony structure, articular surfaces, bone marrow, and surrounding soft tissues in comparison with MRI [19].

Ultrasound is well suited for image-guided interventional procedures including injection of the joint, tendon sheaths, or bursa; drainage of para-articular fluid collections; and treatment of calcific tendinosis [17]. Continuous imaging during aspiration or injection helps us to verify a proper positioning of the needle tip. The problem is the impossibility to reevaluate the images of the hip later, and a very experience ultrasonographist must be present.

MRI is a secondary diagnostic method of choice in the evaluation of adult painful hip which provides excellent information about soft tissue and bone marrow abnormalities which are not seen on plain radiograph, CT, ultrasonography, or nuclear medicine exams. MRI is effective in demonstrating intra-articular and extra-articular pathology. Intra-articular disorders that are well demonstrated with MRI include osteonecrosis, stress fracture, occult fractures, joint effusions, osteoarthritis, and inflammatory arthropathies [20–23]. Different extra-articular pathologies such as pubic osteitis, sacroiliitis, bursitis, myotendinitis, and occult pelvis neoplasm may also be well recognized on MRI. In recent years, poor success has been demonstrated in the detection of labral tears and cartilage lesion on conventional MRI at 1,5 T, but this may improve with 3T MRI and with newer imaging techniques [3, 24]. Future improvements in MRI technology may lead to successful noninvasive evaluation of these structures. Studies in recent years have shown that 3T MR arthrography is much more beneficial in the detection of labral tears in comparison with conventional 3T MRI [6, 25]. Although MR arthrography is an excellent positive predictor in diagnosing acetabular labral tears and cartilage abnormalities, it still has limited sensitivity. A negative imaging study does not exclude the presence of intra-articular pathology that can be identified and treated arthroscopically [26].

Protocols for MRI of the hip vary among institutions and with the type of scanner used. The quality of the examination depends on the field strength of scanner, coil selection, technical parameters used, and whether or not dedicated small-field-of-view images of the hip are acquired. MRI protocols are adapted to the clinical presentation. For instance, at our institution, the typical exam for an adult with unexplained hip pain includes seven sequences and is tailored toward evaluating intra-articular and extra-articular pathology. The coronal T1-weighted images of both hips reveal anatomy and marrow-based pathologies such as occult fractures, tumors, or osteonecrosis. The T2-weighted fat-suppressed images of both hips demonstrate myotendinous injuries, intra-articular or extra-articular fluid collection such as bursitis and joint effusions, depict stress fracture and occult fracture, subchondral cyst, osteonecrosis, and tumor as marrow-based changes. For the detection of cartilaginous and labral lesions, it is essential to create small-field-of-view high-resolution imaging of the affected hip [12]. The oblique sagittal SPGR sequences are used to measure for the cam and pincer FAI and to assess for the characteristic osseous bump present with the cam FAI.

Magnetic resonance arthrography (MRA) of the hip is a diagnostic method of choice of unexplained adult hip pain in the event that we suspect intra-articular pathologies. Several reports have documented the success of MRA of the hip in detecting cartilage and labral injuries [3, 5, 14, 27, 28]. MRA can also depict abnormalities of ligamentum teres and joint capsule and demonstrate the presence of loose bodies or proliferative changes of synovitis. In comparison with conventional MR, MR arthrography allows better visualization of intra-articular anatomy because the intra-articular application of the fluid displaces the joint capsule from the underlying bone and normal structures. Leakage of contrast into the labrum or cartilage is direct evidence of pathology of these structures [24]. MRA of the hip is thus helpful when conventional MR is noncontributory and when there is clinical suspicion of labral or other intra-articular pathologies.