Indian Journal of Rheumatology

REVIEW ARTICLE
Year
: 2018  |  Volume : 13  |  Issue : 5  |  Page : 29--35

Ultrasound of the hip in rheumatology


Girish Gandikota, Moe Tun 
 Department of Radiology, University of Michigan Hospitals, Ann Arbor, MI, USA

Correspondence Address:
Prof. Girish Gandikota
Department of Radiology, Division of Musculoskeletal Imaging, 1500 E. Medical Center Drive, TC 2910S, Ann Arbor, MI 48109
USA

Abstract

Recent advances in musculoskeletal (MSK) ultrasound and transducer technology have enabled increased utilization of high-quality ultrasound in rheumatology clinics and by the bedside as an adjuvant to the clinical examination of the hip. Ultrasound is also an integral part of image-guided joint aspirations, injections, biopsies, and bursa injections. In this article, we will focus on basic ultrasound scanning technique and findings related to common rheumatologic pathologies of the adult symptomatic hip. Transducer positioning and essential sonographic bony landmarks will be reviewed and scanning in two orthogonal planes (both long and short axes of the structure) will be emphasized. Common hip pathologies such as synovitis, joint effusion, bursitis, greater trochanter pain syndrome, and hamstring pathology will be discussed. The reader will also be made aware of limitations of ultrasound in the evaluation of hip and emphasize the complementary role of ultrasound with other imaging modalities (radiographs, computed tomography, and magnetic resonance imaging). The diagnostic ability of MSK ultrasound is based on an operator's training and experience, the patient's habitus, and aptly chosen clinical indications. A good grasp of anatomy, sound ultrasound technique, and knowledge of limitations of ultrasound modality are essential for a safe ultrasound practice. A long-standing commitment of time and resources is needed to become competent and comfortable in scanning. Where possible, the training should be inbuilt into the postgraduate training. It is best that a rheumatologist adopts a career plan of learning, inclusive of MSK ultrasound, relevant to rheumatology.



How to cite this article:
Gandikota G, Tun M. Ultrasound of the hip in rheumatology.Indian J Rheumatol 2018;13:29-35


How to cite this URL:
Gandikota G, Tun M. Ultrasound of the hip in rheumatology. Indian J Rheumatol [serial online] 2018 [cited 2020 Sep 18 ];13:29-35
Available from: http://www.indianjrheumatol.com/text.asp?2018/13/5/29/238199


Full Text



 Introduction



Clinical evaluation of a deep-seated joint, such as the hip, can be very challenging and often difficult. Recent advances in musculoskeletal (MSK) ultrasound and transducer technology have enabled increased utilization of high-quality ultrasound in rheumatology clinics and by the bedside as an adjuvant to the clinical examination of the hip. High-frequency MSK ultrasound not only offers a dynamic real-time evaluation of peri- and intra-articular inflammatory activity, but also allows immediate comparison to the contralateral side for assessing the relevance and severity of the findings. In this article, we will focus on basic ultrasound scanning technique and findings related to common rheumatologic pathologies of the adult symptomatic hip.

 Indications



Common diagnostic rheumatological indications of MSK ultrasound in the adult hip include the following:

Anterior hip:

Joint effusion/synovitisIliopsoas bursa pathology.

Lateral hip:

Greater trochanter (GT) pain syndromeTrochanteric bursa.

Posterior hip:

Hamstring pathologyIschiogluteal bursitis.

Ultrasound is also an integral part of image-guided joint aspirations, injections, biopsies, and bursa injections.

 Technical Equipment



For a patient of average build, the linear transducer of 9–12 MHz is preferred. For the assessment of a larger patient, a low-frequency curvilinear transducer (5–8 MHz) may be needed. It is important to choose the appropriate frequency of the transducer and to know how to optimize the image (depth, focus, and gain) for obtaining the best possible diagnostic sonographic information.

 Scanning Techniques



Knowledge of the bony landmarks of the hip (anterosuperior and anteroinferior iliac spine [AIIS], pubic tubercle, GT, and ischial tuberosity) is essential to good scanning technique as they provide orientation and understanding of the underlying sonographic anatomy and help with reproducibility of images [Figure 1]a and [Figure 1]b. The structure to be examined should be evaluated in at least two orthogonal planes: one along its long axis and the other along the short axis (by turning 90° perpendicular to the long-axis imaging plane). The emphasis should also be on proper patient positioning while keeping patient comfort in mind. This is essential in obtaining good diagnostic images. Ultrasound evaluation of the hip is usually focused, scanning the symptomatic region (anterior, posterior, lateral, or medial).{Figure 1}

 Anterior hip



Patient position:

Supine, hip, and knee extended, foot neutral/slight external rotation.

Transducer position:

The transducer is positioned superoinferiorly, over the anterior hip/groin, lateral to the femoral vasculature, along the long axis of the femoral head and neck [Figure 2]a and [Figure 2]b.{Figure 2}

Anatomy assessed:

JointJoint capsuleLabrumIliopsoas tendon and iliopsoas bursaRectus femoris (RF).

Helpful in the diagnosis of:

Joint effusionSynovitis/synovial pathologyErosions/intra-articular bodies/osteophytesParalabral cyst/labral tearIliopsoas bursaCalcific tendinosis of RF.

Joint effusion versus synovitis

Outcome Measures in Rheumatology (OMERACT) defines effusion or synovial fluid as abnormal hypoechoic or anechoic (relative to subdermal fat, but sometimes may be isoechoic or hyperechoic) intra-articular material that is displaceable and compressible but does not exhibit Doppler signal.[1]

OMERACT defines synovitis or synovial hypertrophy as abnormal hypoechoic (relative to subdermal fat, but sometimes may be isoechoic or hyperechoic) intra-articular tissue that is nondisplaceable and poorly compressible when pressure is applied via the transducer which may exhibit Doppler signal.[1] Although compressibility can be elicited in most superficial joints, due to its depth, this is usually not applicable in the adult hip joint.

It is important to carefully analyze and distinguish between joint effusions and synovitis in patients with inflammatory arthritis as it can affect clinical management.

Joint pathology (effusion, synovitis, and intra-articular bodies) is best imaged anteriorly along the long axis of the femoral neck. The hyperechoic continuous line of the bony cortex of the femoral head and neck can be clearly visualized [Figure 2]b. The joint capsule appears as hyperechoic soft tissue extending over the neck with an intervening recess. Normally, the anterior recess of the hip joint measures up to 7 mm,[2] representing the space between the hyperechoic capsule and anterior femoral neck [3] [Figure 3]a. The effusion and/or synovitis results in the increased distance between the cortical outline of the anterior femoral neck and the overlying joint capsule. With increasing joint effusion or synovial pathology, the anterior capsule bulges outward and assumes convex configuration [Figure 3]b.{Figure 3}

Pitfalls

When hip is in internal rotation (assumed when the big toe is pointing medially), it can be associated with the convex outline of the anterior joint capsule and the anterior joint recess may artifactually measure >7 mm in thickness.[4] This is often wrongly diagnosed as a joint effusion, where none actually existsIf the transducer is not placed correctly along the long axis of the femoral neck, or if the transducer gain is not set correctly, the synovium may appear significantly hypoechoic and may simulate joint fluid. Furthermore, care should be taken to avoid anisotropy, where possible, by correcting the angle of the transducerThere is always some intra-articular tissue anterior to the femoral neck, which can be normal. Normally, the capsule is not distended (i.e., not convex outline). It is important to resist overdiagnosing synovitis or effusion.

Joint fluid or synovial lining sampling is best performed along the anterior hip with the transducer positioned along the long axis of the femoral neck [Figure 4].{Figure 4}

Osteophytes/erosions

Erosion on ultrasound is defined as a discontinuity of the articular surface or cortex, >2 mm in diameter, visualized in two orthogonal planes.[1] An osteophyte, on the other hand, is a focal osseous protuberance from the articular surface. While assessing for joint effusion, the head-and-neck junction should be carefully examined for cartilage abnormalities, rim osteophytosis, and/or erosions [Figure 5]a. Then, when the transducer is moved superiorly over the femoral head in the same plane, the bony acetabulum (anterior inferior margin) is encountered, enveloping the superior portion of the femoral head. This is the ideal location for assessment of a labral tear, paralabral cyst, acetabular rim osteophytes, joint space narrowing, cortical irregularity, and erosive changes of the femoral head. These findings would complement the radiographic findings.{Figure 5}

Labral tear

When sonographically evaluating the anterior hip joint, the hyperechoic triangle-shaped superior hip labrum is seen, attached to the acetabular rim, lying deep to the hip capsule [Figure 5]b, partially overlying the femoral head.[5] Medially, it is seen extending deep to iliopsoas tendon. Labral degeneration can be seen as a hypoechoic or heterogeneous area within the labrum with loss of normal triangular labral morphology. A labral tear is seen as a more defined intrinsic anechoic cleft.[6] A lobulated cystic structure in contact with the acetabular bone, extending proximally from the region of the labrum at the hip joint, should raise concern for a paralabral cyst secondary to labral tear [Figure 6].{Figure 6}

Pitfalls

Ultrasound is not the gold standard for diagnosing labral tears. Magnetic resonance imaging (MRI) should be considered if confirmation is necessary. Labral tears are not uncommon in patients over 50 years old and often asymptomatic and part of a degenerative processA paralabral cyst should not be diagnosed as a joint effusion.

Iliopsoas and rectus femoris pathologies

The iliopsoas complex is best identified in a transverse plane. The transducer orientation is horizontal to the groin, best achieved by rotating 90° from the long axis position along the femoral neck [Figure 7]a and [Figure 7]b. The iliopsoas complex contains the tendon portion (often appearing as two tendons; the larger medial one is the psoas tendon and smaller lateral one is the iliacus tendon), which is hyperechoic and the iliopsoas muscle that is located mostly anterior to the tendon. The iliopsoas tendon does not have a tendon sheath, hence no tenosynovitis.{Figure 7}

Along with the iliopsoas complex, the iliopsoas bursa can be evaluated for bursa distension or bursitis. It is located deep to the psoas tendon overlying the acetabulum and inner pelvic wall. In most cases, this bursa is a potential space and does not contain any sizable fluid. Iliopsoas bursa can communicate with hip joint in about 15% of cases, in which case, joint fluid can track into the bursa. In the inflammatory arthritis patient population, this communication is even higher.[7] It is imaged in a similar fashion to that of iliopsoas tendon, in both transverse and longitudinal planes [Figure 8]a and [Figure 8]b. A distended iliopsoas bursa can appear as a bilobed structure, on either side of the psoas tendon, when imaged in short axis, with the transducer placed transversely in the groin. In long-axis view, the distended bursa is located deep into iliopsoas tendon and superficial to the hip joint capsule. Ultrasound guidance is often utilized for iliopsoas bursa injections.{Figure 8}

The RF attaches to the superior acetabulum via straight and reflected heads. The straight head (also called direct head) attaches to the AIIS and the reflected head (also called indirect head) attaches to the superolateral margin of the acetabulum. The reflected head is a common site of calcific tendinosis.[8] These attachment sites are also prone to enthesitis, tearing, and tendinosis. To find the direct head of the RF, identify the AIIS, a bony protuberance of the ilium, just proximal to the anterolateral acetabulum. The transducer is moved superolaterally from its initial longitudinal position over the femoral head–acetabulum junction until the bony outline of AIIS is visualized. The indirect head of the RF can be seen if the transducer is moved further laterally and just inferior to the AIIS.

Enthesitis, inflammation at the bony attachment sites of the tendons, ligaments, and joint capsule, is also an important feature of inflammatory arthritis, specifically spondyloarthropathy. Enthesopathy is defined as a hypoechoic (loss of normal fibrillar architecture) thickened tendon or ligament at its bony attachment, seen in two perpendicular planes, that may exhibit Doppler signal and/or bony changes including enthesophytes, erosions, or irregularity.[1] The tendinous attachment site of the direct head of the RF muscle should be assessed for enthesopathy changes in a patient presenting with anterior hip pain [Figure 9].{Figure 9}

Lateral

Patient position:

Hips and knees gently flexed in a lateral decubitus position [Figure 10]a. Placing the pillow between knees helps with comfort.{Figure 10}

Transducer position:

The GT, a palpable bony prominence along the proximal lateral femur, is an important landmark in the lateral hip examination. The transducer is placed transversely over the lateral aspect of the proximal femoral shaft and scanned upward till the triangularly shaped GT protuberance is encountered [Figure 10]a and [Figure 10]b.

Anatomy accessed:

Gluteal tendinopathy and intervening bursitis trochanteric bursa [Figure 11].{Figure 11}

Gluteal tendinopathy and bursitis

The most anterior of three gluteal tendons, the gluteus minimus, inserts onto the anterior facet of the GT [Figure 12]a and [Figure 12]b. Gluteus minimus bursa is a potential space deep to the gluteus minimus tendon, between gluteus minimus and anterior facet. The lateral facet of the GT provides attachment to the lateral fibers of gluteus medius tendon. Deep to these fibers lies the gluteus medius bursa. The majority of the gluteus medius fibers, however, attach to the superior facet of the greater tuberosity, best appreciated in its long axis, with the posterior translation of vertically oriented transducer [Figure 13]a and [Figure 13]b. (The transducer is turned 90° from the transverse position.) Both gluteus medius and minimus should also be assessed in their longitudinal planes. Gluteus maximus does not attach to the GT, but its muscle belly drapes over the posterior facet of the GT [Figure 11].{Figure 12}{Figure 13}

The lateral hip pain is usually secondary to gluteal minimus and medius pathology (tendinosis, tear) and less likely from trochanteric bursitis.[9] Gluteus maximus attaches to the posterior shaft of the femur, distal to the GT, and is a recognized site of calcific tendinosis in the posterolateral hip. Gluteus medius and minimus tendon attachment sites can also be the site for calcific tendinosis [Figure 14]a and [Figure 14]b.{Figure 14}

Posterior

Patient position:

Prone with the hip and knee extended.

Transducer position:

The ischial tuberosity is a palpable bony prominence in the posterior hip, close to the midline, corresponding to the horizontal gluteal crease. Ultrasound assessment of the posterior hip can begin with placing the transducer transversely between the GT and ischial tuberosity [Figure 15]a and [Figure 15]b to look for hamstring tendons and sciatic nerve, then following these structures distally in the posterior thigh.{Figure 15}

Anatomy accessed:

Hamstring tendons and sciatic nerve.

Hamstring pathology

The hamstrings, namely, the long head of the biceps femoris, semimembranosus, and semitendinosus, insert onto the ischial tuberosity. Semitendinosus and the long head of the biceps femoris fuse and attach as a conjoint tendon on the medial aspect of the ischial tuberosity. Semimembranosus tendon attaches separately to the lateral aspect of the ischial tuberosity [Figure 15]c.

Similar to the gluteal tendons, tendinosis, partial tear, and bursitis around the hamstring tendons could be the cause of the symptoms and should be inspected in patients with a history of an inflammatory arthritic disease, presenting with posterior hip pain [Figure 16]a and [Figure 16]b. The sciatic nerve lies in proximity to the proximal hamstrings, mid-way between the ischial tuberosity and the GT [Figure 15]b. Given the proximity, pathology of proximal hamstrings can extend to involve the sciatic nerve.{Figure 16}

 Future Direction



MSK ultrasound is undeniably an excellent screening tool. In many instances, it provides a definitive diagnosis in hip pathology, thereby minimizing the need for more expensive MRI. Given the direct patient contact, ultrasound findings can be immediately correlated with symptomatology. Ultrasound is being increasingly relied upon as an imaging modality guiding interventions and the trend is likely to continue. In the future, ultrasound, like a stethoscope, will become an integral part of the clinical examination of the hip. The advancement in technology and affordability are promising trends leading to the wider application of ultrasound. The diagnostic ability of MSK ultrasound is based on an operator's training and experience, the patient's habitus, and aptly chosen clinical indications. A good grasp of anatomy, sound ultrasound technique, and knowledge of limitations of ultrasound modality are essential for a safe ultrasound practice. A long-standing commitment of time and resources is needed to become competent and comfortable in scanning. Where possible, the training should be inbuilt into the postgraduate training. It is best that a rheumatologist adopts a career plan of learning, inclusive of MSK ultrasound, relevant to rheumatology.

Acknowledgments

The authors would like to thank Danielle Dobbs for the illustrations and Vanessa Allen for her assistance in figure preparation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Wakefield RJ, Balint PV, Szkudlarek M, Filippucci E, Backhaus M, D'Agostino MA, et al. Musculoskeletal ultrasound including definitions for ultrasonographic pathology. J Rheumatol 2005;32:2485-7.
2Koski JM, Anttila PJ, Isomäki HA. Ultrasonography of the adult hip joint. Scand J Rheumatol 1989;18:113-7.
3Robben SG, Lequin MH, Diepstraten AF, den Hollander JC, Entius CA, Meradji M, et al. Anterior joint capsule of the normal hip and in children with transient synovitis: US study with anatomic and histologic correlation. Radiology 1999;210:499-507.
4Jacobson JA, Khoury V, Brandon CJ. Ultrasound of the groin: Techniques, pathology, and pitfalls. AJR Am J Roentgenol 2015;205:513-23.
5Blankenbaker DG, De Smet AA, Keene JS, Fine JP. Classification and localization of acetabular labral tears. Skeletal Radiol 2007;36:391-7.
6Jin W, Kim KI, Rhyu KH, Park SY, Kim HC, Yang DM, et al. Sonographic evaluation of anterosuperior hip labral tears with magnetic resonance arthrographic and surgical correlation. J Ultrasound Med 2012;31:439-47.
7Wunderbaldinger P, Bremer C, Schellenberger E, Cejna M, Turetschek K, Kainberger F, et al. Imaging features of iliopsoas bursitis. Eur Radiol 2002;12:409-15.
8Rajiah P, Ilaslan H, Sundaram M. Radiologic case study. Calcific tendinitis of the rectus femoris with intraosseous extension of calcification. Orthopedics 2011;34:329.
9Kong A, Van der Vliet A, Zadow S. MRI and US of gluteal tendinopathy in greater trochanteric pain syndrome. Eur Radiol 2007;17:1772-83.