diagnostic ultrasound of the hip
introduction
Moving forward in our ultrasound series after the wrist and hand, the hip diagnostic scan will be covered in this week’s post. The hip structures can be deeper than the areas covered to this point and the transducer may change depending on the patient’s body habitus. The operator should use the highest possible frequency that provides adequate presentation. Diagnostic ultrasound of the hip can be used in both adults and children, but the focus will remain strictly with adults in this post.
The most common applications for US in the adult hip are the detection of tendon and muscle injuries, the identification of effusion or synovitis within the hip joint or its adjacent bursae and the guidance for the treatment of these findings. Because the hip examination in the adult is focused on clinical symptoms, most subdivide the hip area into a four quadrant approach including its anterior, medial, lateral and posterior aspects. In general, anterior and lateral structures are superficial and readily accessible, whereas posterior structures are deep-seated and, therefore, much more difficult to be examined with this technique. Color and power Doppler imaging may be useful in detecting hyperemia within the joint or surrounding structures.
Potential causes of anterior hip pain extend from the pubic symphysis to the hip joint itself. Patients with lateral hip pain most frequently require an examination of the gluteal insertion and associated bursae. Posterior pain could be due to abnormalities extending from the hamstring attachment to the ischium to the posterior aspect of the hip joint.
anterior hip
For the anterior hip exam, the patient will be supine. The primary structures that need evaluation include the hip joint and recess, iliopsoas tendon and bursa, proximal thigh musculature origin (rectus femoris and sartorius) and pubic symphysis. The exam begins with the transducer long axis to the femoral neck (oblique-sagittal plane). The femoral shaft will have a curved and echogenic surface. The transducer should be moved proximally until the greater trochanter and lesser trochanter are identified. The transducer is turned to parallel the femoral neck. The hip joint is identified on the long axis to the femoral neck and the anterior joint recess should be evaluated for fluid or synovial abnormalities. The anterior hip capsule extends inferiorly from the labrum and inserts at the intertrochanteric line and measures 2-3 mm each in thickness.
Image 1. Anterior hip scan starting position. Adopted from [3].
The iliopsoas region is evaluated by moving the transducer in the transverse plane over the femoral head. One can easily see the anterior inferior iliac spine (AIIS) when moving superior (witch’s hat). The transducer can be moved inferiorly until the iliopsoas tendon comes into view and toggling the transducer may visualize the tendon as hyperechoic and sitting over the femoral head and acetabulum. Medial to the hip joint lies the femoral vasculature (can follow NAVEL (nerve, artery, vein, empty space, lymphatic)).
Image 2. Probe placement and iliopsoas tendon sheath at needle tip. Adopted from [2].
Video 1. Anterior hip US. Femoral head and neck in view to start and then probe moved medially with the iliac vessels seen over the far right and iliopsoas tendon focused in view near the end of the video.
When a “snapping hip” is suspected, dynamic scanning is performed over the region of interest using the same movement that the patient describes as precipitating the complaint. The snapping hip is usually related to the iliopsoas tendon as it passes anteriorly over the superior pubic bone or laterally where the iliotibial tract crosses the greater trochanter. The probe is placed in the transverse plane and the majority of individuals can reproduce the snapping with flexion, abduction and external rotation motion passively or actively.
Image 3. Transverse oblique sonograms of the anterior aspect of the hip joint. During neutral position of the limb the iliopsoas tendon (straight arrow) adjacent to the iliopectineal eminence (*). During hip flexion, abduction, and external rotation the iliopsoas tendon moves away from the bone (oval shape). When the limb comes back to neutral position, the iliopsoas tendon (curved arrow) follows the reverse path and snaps abruptly against the iliopectineal eminence Adopted from [2].
The rectus femoris origin can be evaluated by placing the probe back onto the AIIS in the transverse plane and moving laterally. The direct head is in this space and the indirect head is at the lateral aspect of the acetabulum. The transducer is moved in the short axis relative to the rectus femoris direct head and moved proximally and laterally to visualize the sartorius and its origin on the anterior superior iliac spine (ASIS). The lateral femoral cutaneous nerve (responsible for meralgia paresthetica) can then be seen by moving the transducer in the transverse plane over the proximal sartorius and moving distally. The lateral femoral cutaneous nerve can be seen as several nerve fascicles coursing over the sartorius from medial to lateral. It is then seen in a triangular hypoechoic fatty space slightly distal and lateral.
Image 4. Rectus femoris probe positioning and technique. Adopted from [3]
Image 5. Lateral femoral cutaneous nerve. Adopted from [3]
In some academic sources, the adductor or anterior thigh exams are done separately, but many athletes can suffer from issues with the adductors. The patient can move into a frog leg position with the hip and knee flexed and the hip externally rotated. The probe can be placed over the anteromedial aspect of the thigh along the short axis of the adductors and then rotated into its long axis. The provider can then tract superiorly until the pubic symphysis and common adductor tendon are seen. More laterally, the adductor muscle originating from the inferior pubic ramus can be evaluated along with the pubic symphysis more medially.
The adductor musculature can then be evaluated by moving the probe distally. Three adductor muscles are found from anterior to posterior with the adductor longus, brevis and magnus. The common adductor tendon is usually split by this point, the larger anterior component being the tendon of the adductor longus. The gracilis overlies the adductors and can be evaluated here.
Image 6. Adductor musculature ultrasound and location of obturator nerve. Adopted from [2].
lateral hip
The lateral hip can be evaluated next and the patient can roll towards the opposite hip to access the posterolateral hip. The transducer is placed over the lateral hip and begins over the greater trochanter (GT) in the short axis to the femur. A key landmark is the apex of the greater trochanter between the anterior and lateral facets. Posterior to the lateral facet is the posterior facet of the GT. The insertion of the gluteus medius is on the anterior facet and the gluteus medius is over the lateral facet. The iliotibial tract can be evaluated superficial to the gluteus medius tendon.
One should evaluate the greater trochanter facets in the short and long axis and the operator should position and adjust to eliminate anisotropy. The transducer should be positioned so the cortex of each individual facet is perpendicular to the sound beam. The subgluteus medius bursa, subgluteus minimus bursa and the subgluteus maximus bursa are located between each tendon and facet. For evaluation of the gluteus medius tendon in the long axis, the transducer is first positioned over the anterior facet in the short axis and turned ninety degrees. The same technique is used over the lateral facet to evaluate the gluteus medius tendon in long axis.
Image 7: The slightly pointed configuration of the lateral aspect of the proximal femur separates the facet when gluteus minimus inserts (anteriorly) from the medial facet, where the lateral fibers of gluteus medius attach. Adopted from [2].
Image 8. Additional view of greater trochanter more distally with insertions shown. Adopted from [1].
Video 2. Greater trochanter initially in long axis and then turned ninety degrees for second half of video to fully evaluate the bursa/facets.
posterior hip
The patient can then be asked to lie prone for the evaluation of the posterior hip. The gluteal attachments are identified in the axial plane and the probe can be moved medially until the ischial tuberosity is encountered. Between the space between the posteromedial margin of the tip of the greater trochanter and the ischial tuberosity lies the hamstring origin medially, quadratus femoris centrally. Deep to this lies the tendon of the obturator externus. The quadratus femoris and the obturator externus occupy the ischiofemoral fossa in which muscle impingement can occur if this space is narrow (ischiofemoral impingement).
Image 9. Posterior hip probe positioning. Adopted from [3].
The probe can then be moved proximally and the gemelli muscles can be evaluated overlying the hip joint. Deep to the gemelli muscles, the contour of the femoral head and posterior acetabular wall can be seen and fluid in the posterior joint space can be located here.
Image 10. (A) the quadratus femoris muscle(arrowheads) , obturator externus (arrow) , and sciatic nerve (open arrow) deep to the gluteus maximus. The transducer is moved cephalad to show (B) the inferior gemellus (I) . Moving more cephalad (C) the obturator internus (curved arrow) is seen coursing medial over the ischium ( IS ) (using a curvilinear transducer). In short axis (D), from superior to inferior is identified the superior gemellus (S) , obturator internus (curved arrow) , inferior gemellus (I) , quadratus femoris (arrowheads) , and obturator externus (arrow). Adopted from [1].
To evaluate the remaining structures, the operator can start at the spinous process of L5 and the sacrum. The probe can be moved laterally to visualize first the posterior sacral foramina and the sacroiliac joint. The superior aspect of the sacroiliac joint is widened at the fibrocartilage or ligamentous articulation, whereas the synovial articulation is narrow. The probe can be moved to the transverse plane, moved inferiorly and laterally to identify the piriformis in the long axis. The muscle belly will be located medial to the ilium and the tendon will be directly over the ilium. The observer can passively rotate the hip to assist in the identification of the piriformis tendon sheath. The sciatic nerve can be seen inferior to the piriformis and can be evaluated here.
Image 11. US images in the transverse plane over (A) the upper and (B) lower sacrum show the left SI joint (arrows), posterior sacral foramen (open arrow) and posterior ilium (I). (C) shows oblique US with piriformis tendon (arrowheads) and muscle (D). Adopted from [1].
Summary
The diagnostic ultrasound of the hip serves multiple purposes in a sports medicine clinic, including additional uses such as evaluation of the prosthetic hip and pediatric hip. The development and refinement of ultrasound (US) transducers have improved the capability of US to examine tissues, and US is accepted as a primary means of examining the musculoskeletal system. Its low cost, availability, noninvasive nature and the possibility of a dynamic examination make US an excellent imaging technique to investigate a wide range of conditions affecting the hip.
References
- Jacobson, J. (2018). Fundamentals of Musculoskeletal Ultrasound. Elsevier.
- McNally, E. (2014). Practical Musculoskeletal Ultrasound (2nd ed.). London: Elsevier Health Sciences UK.
O’Neill, J., Glickman, A. (2008). Musculoskeletal Ultrasound Anatomy and Technique. Springer, New York, NY.
