Hip Ultrasound

G Model EURR-5474; No. of Pages 8 ARTICLE IN PRESS

European Journal of Radiology xxx (2011) xxx–xxx

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European Journal of Radiology

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Hip ultrasound

Carlo Martinoli a,∗, Isabella Garello a, Alessandra Marchetti a, Federigo Palmieri a, Luisa Altaﬁni a, Maura Valle b, Alberto Tagliaﬁco c a Radiologia, DISC, Università di Genova, Largo Rosanna Benzi 8, I-16132 Genoa, Italy b Radiologia, Gaslini Children Hospital, Genova, Italy c Radiologia, National Institute for Cancer Research, Genoa, Italy article info abstract

Article history: In newborns, US has an established role in the detection and management of developmental dys- Received 16 February 2011 plasia of the hip. Later in childhood, when the limping child is a major diagnostic dilemma, US is Accepted 22 March 2011 extremely helpful in the identification of the varied disease processes underlying this condition, as transient synovitis, septic arthritis, Perthes disease and slipped femoral capital epiphysis. In adoles- Keywords: cent practicing sporting activities, US is an excellent means to identify apophyseal injures about the Hip joint pelvic ring, especially when avulsions are undisplaced and difficult-to-see radiographically. Later on, in Ultrasound the adulthood, US is an effective modality to diagnose tendon and muscle injuries about the hip and Developmental dysplasia of the hip Irritable hip pelvis, identify effusion or synovitis within the hip joint or its adjacent bursae and guide the treatment Apophyseal injuries of these findings. The aim of this article is to provide a comprehensive review of the most common Hip tendon disorders pathologic conditions about the hip, in which the contribution of US is relevant for the diagnostic Hip joint synovitis work-up. US-guided interventional procedures © 2011 Elsevier Ireland Ltd. All rights reserved.

Owing to its anatomic complexity, the hip is a challenging site specific clinical contexts in which US plays a key role in the diag- for evaluation with ultrasound (US). In children, US is the technique nosis and patient management. of choice for screening, diagnosis and treatment of developmental dysplasia of the hip, it plays an important role in the assessment of 1.1. Developmental dysplasia of the hip the irritable hip and hip infection as well as in detection of sporting injuries causing apophyseal avulsion about the pelvic ring. In the Developmental dysplasia of the hip is a condition involving adult population, US is increasingly used mainly to detect intraar- deformity of the acetabulum at various degrees, possibly lead- ticular joint effusion and to evaluate paraarticular masses, tendon ing to subluxation or dislocation of the femoral head [1]. The and nerve disorders. This article provides an overview of the role reported incidence of this condition accounts for approximately of US to examine a wide range of disorders about the hip that can 2–6:1000 live newborns [1]. Several constitutional (e.g., female occur in children and adults. gender, white race), mechanical (e.g., oligohydramnios, breech delivery) and functional (e.g., maternal estrogen levels, familiar- ity) factors seems to be predisposing. In the newborn, reducing 1. Paediatric hip a prenatal dislocation may lead a stable hip to develop. How- ever, if dislocation is not recognized early, some adaptive changes US is an extremely efficient imaging modality to examine the make the femoral head more difficult to reduce. An early diagno- paediatric hip, as an exquisite depiction of the immature skele- sis of developmental dysplasia of the hip is, therefore, critical for ton with large amounts of cartilaginous bone can be obtained in establishing a proper treatment [2]. Physical examination is based children in a well-tolerated and noninvasive way. In addition, this on inspection and two basic stress tests, the Ortolani and Barlow technique is very sensitive to detect hip joint effusion and can aid manoeuvres [1]. The accuracy of physical examination is, however, joint aspiration in a variety of clinical settings. Developmental dys- not absolute with <1% reported misdiagnoses [3]. Owing to intrinsic plasia of the hip, irritable hip and apophyseal traction injuries are limitations of radiography related to the use of ionizing radiations and the unossified status of the relevant bony landmarks, US has been proposed as an efficient alternative to diagnose developmen- ∗ Corresponding author. Tel.: +39 3355614449; fax: +39 010 555 6620. tal dysplasia of the hip. Basically, two methods have been developed E-mail address: [email protected] (C. Martinoli). to image the neonatal hip with US: static (Graf, Morin, modified

Fig. 2. Irritable hip. (A) Transient synovitis. Long-axis US image over the anterior femoral neck in a 8 year-old child demonstrates a fluid-filled anterior recess (arrows) with convex anterior wall. The iliopsoas muscle (IP) is located superficial Fig. 1. Developmental dysplasia of the hip. (A) Standard coronal US image of the to this recess. (B) Septic arthritis. Long-axis US image over the anterior aspect of the normal infant hip shows the relevant anatomical structures for evaluation of hip hip joint in a 5 year-old child demonstrates overdistension of the anterior recess dysplasia. They are: the hypoechoic rounded femoral head (FH) centered over the (arrowheads) by pseudo-solid echogenic material. The joint capsule is thickened hypoechoic triradiate cartilage (3), the promontory (empty arrow), represented by (arrowheads). Note the femoral head consisting of the ossification center of the the junction between the iliac wing (a) and the bony acetabular roof (b), and the epiphysis (1), the physis (2) and the metaphysis (3) covered by cartilage (4). The fibrocartilaginous labrum (c) in continuity with the acetabular hyaline cartilage (1). iliopsoas muscle (5) lies superficial to the joint. More superficially, the gluteus medius (Gme) is seen. During US examination, the iliac bone must be always kept parallel to the probe, otherwise inaccurate measurements will be made. (B) Frank hip dislocation. Standard coronal US image reveals discloses many immature or unstable hips that will resolve spon- a dislocated femoral head (FH) that does not fit within the cup of the acetabulum. taneously [19,21]. Overall, the question of whether US screening Note the deeper position of the promontory (empty arrow) relative to the femoral head. for developmental dysplasia of the hip is effective and justified is sure to remain a subject of much debate and further research. Morin (Terjesen)) and dynamic (Harcke), as well as a combination of the two (modified Graf (Rosenthal)) [4–7]. These methods have 1.2. Irritable hip proved to be effective and highly accurate in establishing the diagnosis, even if the dynamic technique seems requiring more training The irritable (painful) hip represents a common clinical occur- and practice [8–10] (Fig. 1). In the last decades, US has been selected rence in children [22]. This condition may be related to a variety as the screening procedure for developmental dysplasia of the hip of disorders, including transient synovitis, septic synovitis, Perthes in many countries [5,6,11–15]. Both universal and selective (limited disease and slipped capital femoral epiphysis. This clinical entity to infants with known risk factors) screening programs have been typically presents with acute pain about the hip and the groin, limp- established. In this field, US has proved to be able to detect one third ing and non-weightbearing, limitation of movement and fever. In more abnormalities than the clinical examination [16,17]. Univer- combination with clinical and laboratory parameters, US can play sal screening using the Graf’s method showed that approximately an important role for the diagnostic work-up. Transient synovitis is 75–85% of infants have normal hips, 13–25% have immature hip a benign, self-limiting disorder of unknown origin which represents and 2–4% have dysplastic hips [18,19]. Concerning the association the most prevalent cause for hip pain in children aged 3–8 years. between morphology and stability, 0.1% of normal hips, versus 0.6% Preceding infection of the upper respiratory tract, increased viral of the immature type, 64% of slightly dysplastic and almost 100% antibody titres and some allergic predisposition are linked to this of severely dysplastic undergo dislocation [19]. On the other hand, condition. In these cases, US reveals hip joint effusion distending selective screening limited to infants with risk factors or unstable the anterior recess of the hip joint [23–25]. The fluid distending hip at physical examination was unable to eradicate the onset of the joint is anechoic and not associated with synovial thicken- late cases (accounting for approximately 0.025–0.035%) that occur ing [26] (Fig. 2A). The effusion is considered pathologic when its in a population with normal physical examination around birth and amount is >2 mm in thickness [27]. Patients with transient synovi- no documented risk factors [17,20]. As regard the optimal timing tis have increased risk of developing Perthes disease [28]. Because for screening, it is accepted that scanning too early (4–6 weeks) the ascending cervical arteries pass underneath the anterior joint

Please cite this article in press as: Martinoli C, et al. Hip ultrasound. Eur J Radiol (2011), doi:10.1016/j.ejrad.2011.03.102 G Model EURR-5474; No. of Pages 8 ARTICLE IN PRESS C. Martinoli et al. / European Journal of Radiology xxx (2011) xxx–xxx 3 recess, some pressure exerted on these vessels by the effusion in transient synovitis might be possibly predisposing the femoral head to ischemia. In this setting, the resistive index obtained with spectral Doppler analysis from these vessels has shown to correlate with the amount of effusion and to be markedly elevated (mean, 0.92) compared with asymptomatic hips (mean, 0.58) and other hip disorders [29]. Septic arthritis typically occurs earlier (<3 years-old) than transient synovitis [30]. In neonates, this condition is more often concomitant of femoral osteomyelitis. Staphylococ- cus aureus and gram-negative anaerobes are the most commonly involved agents [22]. Because septic arthritis is a medical emer- gency, a prompt diagnosis and aggressive treatment is required to avoid permanent joint damage. In septic arthritis, US is able to demonstrate hip joint effusion, synovial thickening and cartilage damage and can exclude this condition (but not osteomyelitis) when the anterior recess is free of effusion [22,31,32] (Fig. 2B). The appearance of synovitis is, however, non-specific. In fact, tur- bid fluid, debris, synovial thickening and hyperaemia may be also found in noninfected joints [32,33]. This is the reason for which, in Fig. 3. Apophyseal avulsion. (A) Sagittal US image over a normal anterior superior iliac spine (ASIS) demonstrates the normal origin of the sartorius (arrowhead). (B) suspected septic arthritis of the hip, needle aspiration of hip effu- On the affected side, undisplaced avulsion of the apophysis has occurred. Note the sion remains the key for the diagnosis, even if this policy leads a cortical break (arrow) at the level of injury. substantial number of children with uninfected hips to undergo joint aspiration [22]. In this field, US can help to guide the needle 1.3. Sporting injuries appropriately into the joint space [25]. Perthes disease is the result of idiopathic avascular necrosis of the proximal femoral epiphysis. In children and adolescents, one of the most common site of This condition typically affects 3–12 years-old children with a peak acute apophyseal lesions is the pelvic ring, an area where several incidence at approximately 4–8 years and a definite prevalence musculotendinous structures find their attachment, thus predis- (4:1) in males [34]. In the Perthes age interval, the blood supply posing the immature bone to a wide range of traction injuries. from lateral epiphyseal vessels declines and the contribute from the Apophyseal injuries are most often encountered after 14 years artery in the ligamentum teres is negligible. Hence, the only group of age and usually associated with jumping, sprinting or run- of ascending arteries directed to the femoral head is from the medial ning [47,48]. Injuries typically occur at the cartilaginous growth circumflex artery. Episodes of arterial occlusion or compression plate, resulting in separation and retraction of the partially ossi- from joint effusion (the terminal branches of the medial circum- fied unfused apophysis. Chronic repetitive stresses applied to the flex artery course along the boundaries of the growth plate and apophysis may also be predisposing to an acute injury. Findings are intraarticular), obstructed venous run-off, coagulation abnor- may be subtle if the apophysis is only minimally displaced and malities, longstanding or repeated hip joint effusions have been plain films are often not adequate to establish the diagnosis. If implicated as causative factors [35,36]. US detection of longstand- radiographs are indeterminate, US can be very helpful in identify- ing hip joint effusion (lasting at least 3–6 weeks) and thickening ing minimally displaced or even non-displaced apophyseal injuries. of the cartilage covering the femoral head may help distinguishing In the pelvis, the most commonly involved apophyses are: the Perthes disease from transient synovitis, although these are not secondary ossification center of the iliac crest (abdominal wall absolute discriminatory signs [37,38]. An irregularly fragmented muscles), the anterior superior iliac spine (sartorius and tensor and flattened appearance of the femoral epiphysis as well as wast- fasciae latae), the anterior inferior iliac spine (rectus femoris), ing of the ipsilateral quadriceps muscle can be also shown on US the pubis (adductors), the ischial tuberosity (hamstrings) and the [37,38]. Based on these findings, US has proved able to distinguish lesser trochanter (iliopsoas) [49]. Avulsion injuries at the iliac crest Perthes disease from other causes of painful hip with 99% speci- are typically observed in adolescents practicing sporting activi- ficity, 94% positive predictive value and 95% negative predictive ties before the apophyseal nucleus has fused (18 years of age). value [37]. During healing, US can detect new bone formation ear- Most tears are secondary to a sudden torsion of the body or direct lier than plain films along with the process of revascularization of trauma to the iliac crest [48]. The dislocation occurs anteriorly, the femoral head using contrast-enhanced power Doppler imaging near the anterior inferior iliac spine, with lateral slipping of a [39,40]. Slipped upper femoral epiphysis, a condition also known as chondral-osseous fragment of variable size. Detection of a seg- epiphysiolysis, is a Salter-Harris type-1 injury of the hip occurring mented apophyseal nucleus should be not regarded as a relevant in adolescence as a result of failure of the growth plate cartilage. finding as it can be seen in normal subjects. Avulsion of the ante- Predisposing factors include increased body weight, deep acetab- rior superior iliac spine is observed in adolescents as a result of ulum, decreased anteversion of the femoral head and the status of a forced extension of the hip while the knee is flexed. Plain films intrinsic weakness of the cartilaginous growth plate at the end of demonstrate a small (<2 cm) fleck of bone avulsed from the ante- puberty combined with mechanical stress [41,42]. In undetected rior superior iliac spine that is usually triangular in shape. If the cases, reactive spurring at the metaphyseal level in response to the fragment is barely dislocated, the lesions can be difficult to be rec- conflict with the slipped femoral head and secondary osteoarthritis ognized radiographically. US can show an avulsed fragment (that may occur [43]. In the acute phase, US can identify the disease and on occasion can be palpable) which is most often in continuity with assess the severity of epiphyseal slipping by measuring the width the sartorius tendon rather than with the tensor fasciae latae [50] of the physeal step using an anterior approach and circumferential (Fig. 3). In chronic lesions, hyperostosis and deformity of the ante- scanning around the femoral neck [44–46]. In chronic slips, bone rior inferior iliac spine may occur [48]. If the injury is quite old, remodelling and progressive closure of the physeal step may make the bone can assume a teardrop shape as a result of irregular reat- the US diagnosis more difficult. In any case, the US findings need to tachment of the fragment. Avulsion injury at the anterior inferior be confirmed on plain films. iliac spine occurs rather commonly in adolescents but also in chil-

Fig. 5. Tensor fasciae latae tendinopathy. Longitudinal US image demonstrates focal hypoechoic thickening (arrows) of the tendon origin from the iliac crest.

can be found migrated far away from the ischium. Finally, avulsion injuries of the lesser trochanter at the insertion of the iliopsoas tendon can be seldom encountered in adolescents following sudden eccentric contraction of the iliopsoas tendon while the thigh is extended [48]. In these cases, US can also detect a thin effusion tracking alongside the iliopsoas.

2. Adult hip

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 Fig. 4. Chronic apophyseal injury in a patient with a history of traction traumas at examination in the adult is focused on clinical symptoms, we here the origin of the rectus femoris. A, Sagittal US image over the anterior hip demonstrates the normal profile of the iliac bone with prominence of the anterior superior subdivide the hip area into a four quadrant approach including (ASIS) and anterior inferior (AIIS) iliac spines. The origin of the direct tendon of the its anterior, medial, lateral and posterior aspect [52]. In general, rectus femoris (arrow) from the anterior inferior iliac spine is shown. (B) On the anterior and lateral structures are superficial and readily accessi- affected side, sagittal US image reveals local hyperostotic changes (arrowheads) at ble, whereas posterior structures are deep-seated and, therefore, the tendon insertion (arrow). much more difficult to be examined with this technique. dren practicing soccer or running activities. It involves the direct 2.1. Anterior hip tendon of the rectus femoris following forced resisted extension of the hip. In general, plain films reveal an area of cortical avul- Injuries of anterior thigh muscles at bony attachment sites sion lying inferior to the iliac spine and external to the margin of are common in sporting activities as a result of overuse, micro- the acetabulum due to the action of the intact indirect tendon of traumas or unbalanced contractions [53]. The tensor fasciae latae the rectus femoris [48]. In patients less than 10 years-old, US has tendinopathy is a quite common overuse tendinopathy. The clin- a value to identify purely chondral avulsions. US may also help to ical diagnosis may be suspected in athletes complaining of focal distinguish between avulsion of the anterior superior iliac spine pain radiating below the anterior aspect of the iliac crest. In this that has migrated inferiorly and dislocation of the anterior inferior setting, US can demonstrate a thickened (mean AP size, 4.7 mm iliac spine [50] (Fig. 4). Treatment is usually conservative as the vs. 2.1 mm) and heterogeneous hypoechoic tendon [54] (Fig. 5). degree of fragment dislocation is mild. Apophyseal avulsions from Symptoms can be reproduced during dynamic evaluation. US has the pubis at the origin of the adductors and the rectus abdominis recently demonstrated to be able to depict the complex anatomy may be related to either repeated traction trauma with excessive of the iliopsoas tendon [55]. In particular, this technique is able rotation of the pelvis or resisted abduction of the thigh. Differenti- to visualize five different tendon components based on the ori- ation between adductor injuries and other causes of pubalgia (e.g., gin, trajectory and muscular or tendinous end-point near the lesser osteitis pubis, sacroiliitis, hernias, lesions around the hip joint and trochanter [55,56]. In degenerative tendinopathy, the iliopsoas the acetabular lip) is often difficult. In most instances, a true bone tendon may appear swollen, hypoechoic and heterogeneous. The avulsion does not occur. In the chronic phase, sclerotic changes can snapping hip syndrome is characterized by sudden, painful, and be identified in the pubis at the level of tendon attachment. US is audible snapping of the hip [57]. Certain joint movements, espe- able to identify the retracted tendon end and to distinguish an iso- cially flexion–abduction–external rotation are able to trigger the lated lesion of the adductor longus from extended injuries involving snapping or click. Both intraarticular and extraarticular pathologic more than one muscle. Avulsion injuries at the ischial tuberosity conditions may be responsible for snapping hip [58,59]. The intraar- derive from an excessive eccentric force applied to the origin of the ticular snapping hip may be secondary to loose bodies, synovial hamstring muscles. In general, these injuries are associated with chondromatosis and labral tears. Extraarticular causes involves the intense sport load as it occurs during activities involving forced iliopsoas tendon or the iliofemoral ligament anteriorly, the iliotibial flexion of the thighs on the pelvis (e.g., gymnastics, dance) and band or the gluteus maximus laterally. Dynamic US is well suited present with intense pain in the lower gluteal region and impaired for dynamic evaluation of muscles and tendons around the hip walking. In cases of mild apophyseal displacement, plain films may during joint movement and has been used to correlate the painful be negative. US may reveal caudal displacement of a thin elongated snap with an abnormal iliopsoas tendon motion [60]. In iliopsoas bony fragment that recalls the degree of curvature of the ischium instability, an abrupt sudden medial-to-lateral or lateral-to-medial (ischium epiphysiolysis) [51]. With larger lesions, a bulky fragment motion of the tendon can be visualized dynamically. Mechanisms of

Please cite this article in press as: Martinoli C, et al. Hip ultrasound. Eur J Radiol (2011), doi:10.1016/j.ejrad.2011.03.102 G Model EURR-5474; No. of Pages 8 ARTICLE IN PRESS C. Martinoli et al. / European Journal of Radiology xxx (2011) xxx–xxx 5 snapping iliopsoas tendon include sudden tendon flipping over the iliacus muscle, a bifid tendon with its heads flipping each other and iliopsoas impingement over an anterior paralabral cyst [57]. In case of negative US examination, other imaging modalities such as MR imaging, MR-arthrography or CT scan may rule out intraarticular problems [61]. It is worthy of mention the iliopsoas impingement after total hip replacement. In this setting, impingement is caused by protrusion of the acetabular cup beyond the anteromedial edge of the acetabulum [62]. Cement debris, acetabular screws and bone graft material may be responsible for this condition as well [63]. Proximal rectus femoris injuries usually occur in sportsmen with a history of rectus femoris tendinopathy. Main symptoms include groin pain and loss of extension of the thigh. In the adult population, proximal tears occur less frequently than tears in the midsubstance of the muscle belly involving the central aponeurosis or the level of the deep distal aponeurosis. Complete proximal tears are rare and may mimic a soft-tissue mass as a result of retraction. In chronic injuries, tendon calcifications and haematoma ossification may be observed. In normal states, the iliopsoas bursa is collapsed and cannot be visualized with US. However, hip joint effusion can dis- tend the bursa when excessive intra-articular pressure is present. US can depict the effusion filling the bursa, synovial tissue and loose bodies. Large bursal fluid collections may compress the adjacent femoral nerve [64]. In longstanding rheumatoid arthritis, giant iliopsoas bursitis filled with synovial pannus may mimic a solid paraarticular mass [65]. The iliopsoas bursa should not be mis- taken for paralabral (acetabular) ganglia arising from acetabular labral tears. Different from the bursa, these cysts are lobulated, have internal septa and cannot be compressed with the transducer. Fig. 6. Adductor longus tear. (A) Long-axis US image with B sagittal T2-weighted MR 2.2. Medial hip imaging correlation over the adductor tendon origin reveals avulsion and retraction of the adductor longus tendon (arrow) in association with a small fleck of bone (arrowhead). Note the proximal tendinous bed filled with fluid (asterisks). Adductor injuries are usually diagnosed in relation to overuse sport injuries or acute trauma with a combination of hip hyper- abduction and abdominal wall hyperextension [66]. The adductor longus and the gracilis are the most commonly affected muscles bursa can intervene between the tendon and the greater trochanter. [67,68]. US can demonstrate degenerative changes, partial- and Based on US findings alone, the diagnosis of tendon abnormal- full-thickness tears that usually affect the tendon and the proxi- ities reduces the likelihood of an intraarticular disease as the mal myotendinous junction. Especially in the acute phase, however, cause of hip pain. The first-line therapy for gluteus tendinopa- diffuse groin pain and tenderness may hamper a full confident thy includes rest, physical therapy and local steroid injections. depiction of these injuries with US. Osteitis pubis, prehernia com- In refractory cases and avulsion injuries, surgery with debride- plex, athletic pubalgia with involvement of the rectus abdominis ment and tendon reattachment can be indicated. Peritendinous insertion and adductor insertion avulsion syndrome are the main US-guided corticosteroid injection may be an effective treatment differential diagnoses [63,66–68]. In complete tears, separation of for gluteus medius tendinopathy. This treatment seems effective the adductor longus from the pubis is usually observed (Fig. 6). In in up to 72% of patients one month after the injection [74]. The major traumas, a tear of the adductor longus may involve the super- US-guidance increases the efficacy of local therapy by allowing ficial fibers of the adductor brevis. Distinguishing isolated adductor accurate insertion of the medication in the desired site. The snap- longus tear from a combined adductor longus – adductor brevis ping iliotibial band is an extraarticular snapping condition of the tear is difficult with US. In low-grade injuries and chronic adductor hip caused by intermittent impingement of the posterior border tendinopathy, US has demonstrated low sensitivity in comparison of the fascia lata or the anterior portion of the gluteus maximus to contrast enhanced MR imaging [67]. Both complexity of the tear over the greater trochanter. This condition is similar to the snap- and site of injury are prognostic factors in hip adductor traumas. ping iliopsoas tendon but the snapping sensation is felt laterally. In general, injuries occurring at the level of the musculotendinous In symptomatic patients, hypoechoic thickening of the fascia lata junction are less severe than avulsions or tendon lesions. may be observed, and dynamic US scanning can demonstrate the abrupt and sudden displacement of the fascia lata during specific 2.3. Lateral hip hip movements [75–77]. The lateral aspect of the hip is also the peculiar site of the Morel-Lavallée lesion, a posttraumatic seroma In the context of the greater trochanteric pain syndrome, US can that extends along the trochanteric region and the proximal thigh contribute to distinguish gluteus minimus and medius tendinopa- [78–81] (Fig. 7). This fluid collection derives from an injury of the thy from trochanteric bursitis. Middle-aged and elderly woman are vascular plexus that pierces the fascia lata and expands between the most commonly affected by this condition [69–72]. Signs of the deep layer of the subcutaneous tissue and the fascia. Exces- tendinopathy include focal swelling of the affected tendon por- sive pressure with the probe should be avoided when examining a tion and heterogeneous tendon echotexture. The tendons of the Morel-Lavallée lesion to avoid squeezing the bloody effusion away gluteus minimus and medius can be involved alone or in associa- from the field-of-view of the probe. In chronic lesions, the hetero- tion, with or without trochanteric bursitis [73]. Tendon retraction geneous appearance of the haematoma may resemble a soft-tissue may be observed in complete tears and a haematoma filling the tumour [80].

Fig. 8. Morel-Lavallée lesion. (A) Coronal US image in patient with a previous con- tusion trauma at the lateral aspect of the hip shows a large fluid collection (empty white arrows) with thin strands of fibrin located just superficial to the fascia lata (empty black arrow). VL: vastus lateralis muscle.

2.5. Hip joint and interventional procedures

US plays an important role in detecting intraarticular effusion of the hip because joint distension cannot be palpated owing to the deep position of the anterior recess. Similar to other joints, an articular effusion appears as a fluid collection which shows variable echogenicity depending on the nature of the fluid content (e.g., serous, bloody, infectious). Coxofemoral joint arthrocentesis and aspiration of synovial fluid may be necessary for differential diagnosis between septic arthritis and other joint diseases, such as seropositive and seronegative arthritides and crystal deposi- tion disease. Intraarticular steroid injection is widely performed in patients with ankylosing spondylitis or degenerative joint disease. In order to limit radiation exposure, US is the ideal guidance modality when repeated joint injections should be performed. In this clinical setting, fusion imaging with CT volumetric datasets Fig. 7. Chronic tear of the semimembranosus aponeurosis. (A) Transverse and (B) may help to direct the needle appropriately [87]. Bursal and peri- longitudinal US images of the posterior upper thigh in a patient with an old hamstring injury demonstrate marked hypoechoic thickening of the semimembranosus tendinous US-guided corticosteroid injection may be effective in tendon (arrows) mimicking a soft-tissue mass. Note the normal conjoint tendon of gluteus medius tendinopathy and in iliopsoas tendinosis/bursitis the long head of the biceps and semitendinosus (empty arrowheads) and the sciatic after hip replacement procedure [74,88]. In the last years, the use nerve (white arrowhead). of US has been implemented to perform viscosupplementation in the treatment of hip osteoarthritis [89]. US-guided intraarticular injection of derivatives of hyaluronic acid into the hip joint appears to be safe and well tolerated [89]. 2.4. Posterior hip

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Please cite this article in press as: Martinoli C, et al. Hip ultrasound. Eur J Radiol (2011), doi:10.1016/j.ejrad.2011.03.102