Extraarticular Snapping Hip: Sonographic Findings

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1 Vincent Pelsser 1 Étienne Cardinal 1 Roger Hobden 2 enoit ubin 1 Michel Lafortune 1 Received September 22, 1999; accepted after revision June 8, Department of Diagnostic Radiology, CHUM-St-Luc Hospital, 1058 Saint-Denis St., Montreal, Quebec, H2X 3J4 Canada. ddress correspondence to É. Cardinal. 2 Department of Family Medicine, University of Montreal, 3590, Ontario St. East, Rm. 102, Montreal, Quebec, H1W 1R7 Canada. JR 2001;176: X/01/ merican Roentgen Ray Society Extraarticular Snapping Hip: Sonographic Findings OJECTIVE. The aim of the study was to determine the sonographic findings of snapping hip and to correlate the findings with the presence or absence of pain. MTERILS ND METHODS. Twenty patients with snapping hip were examined with sonography. Conventional and dynamic sonographic examinations of both hips were performed using a 5.0- or 7.0-MHz transducer. RESULTS. Conventional sonographic studies allowed identification of various structural abnormalities (tendinitis, bursitis, synovitis) and helped to document tenderness along the course of specific tendons. Dynamic sonographic studies revealed 26 cases of snapping hip. In 24 of these 26 cases, the underlying cause was clearly identified. Twenty-two snapping hips were caused by an abnormal movement of the iliopsoas tendon, and two were caused by iliotibial band friction over the greater trochanter. One patient reported a bilateral snapping sensation that could not be documented on sonography. Snapping hip was elicited by a wide variety of hip movements. Sonography established an immediate temporal correlation between the jerky tendon motion and the painful snap reported by the patient. Only 14 cases of snapping hip were painful. CONCLUSION. Conventional sonographic studies can identify signs of tendinitis, bursitis, or synovitis. Dynamic sonographic studies revealed the cause of snapping hip in most patients. Snapping hip is characterized on sonography by a sudden abnormal displacement of the snapping structure. In our study, a significant proportion of the cases of snapping hip were not painful. S napping hip was defined by Nunziata and lumenfeld [1] as an audible snapping sound of variable intensity produced during motion of the hip or during waking. It is a challenging clinical condition to diagnose because it may have various intra- or extraarticular causes. The extraarticular causes have been divided into the lateral and the medial varieties. The most common extraarticular causes are the iliotibial band or gluteus maximus snapping over the greater trochanter [2 4] and the iliopsoas tendon snapping over the iliopectineal eminence [5, 6] (Fig. 1). snapping iliopsoas tendon can be revealed radiographically by iliopsoas bursography [7, 8] or tenography followed by fluoroscopy [9]. However, these invasive procedures are sometimes difficult to perform, especially if the bursa is not filled with fluid. Recently, sonography has emerged as a noninvasive technique for examining a snapping iliopsoas tendon [10 12] because it allows dynamic evaluation of soft tissues during motion of the extremity. Snapping hip often comes to the attention of the physician because of a pain-with-motion complaint by the patient. However, some authors have reported that snapping hip could be a painless benign condition without any clinical implications in a certain proportion of patients [1, 6, 13 16]. Consequently, the aim of the present study was to determine the sonographic findings of an extraarticular snapping hip and to correlate the cases of snapping hip with the presence or absence of pain. Materials and Methods Over a 15-month period, we studied 20 consecutive patients with snapping hip (3 males and 17 females; age range, years; mean, 22.1 years) referred either by general physicians specialized in sports medicine or by orthopedic surgeons. Patients had either painful snapping hip (11 patients) or painless snapping hip (7 patients) and were referred for investigation of the origin of the snap. JR:176, January

2 Pelsser et al. Fig. 1. Diagram shows transverse section of right hip. Note relationship among iliopsoas tendon, iliotibial band, and surrounding structures. Sonographic studies were performed by one experienced musculoskeletal radiologist using a curved 5.0-MHz or a linear 7.0-MHz transducer (128-XP; cuson, Mountain View, C). Sonographic evaluation of both hips was performed according to a technique previously described [17]. The anterior aspect of the hip was examined first using transverse and sagittal planes as the patient was lying supine with both legs extended. Oblique sagittal images parallel to the femoral neck were also obtained for evaluation of the hip joint capsule. The medial, lateral, and posterior aspects of both hips were also examined using transverse and sagittal scanning. The medial aspect of the hip was examined by asking the patient to flex, abduct, and externally rotate the hip (frog-leg position). The hip was examined laterally by turning the patient on the contralateral side. Then the posterior aspects of both hips were examined with the patient lying prone. The conventional sonographic study was followed by a dynamic evaluation of both hips with simultaneous video recording as the patient was generating the hip motion that reproduced the snap. For medial snap, this was performed with the patient lying supine with the transducer in a transverse plane over the hip joint or oblique transverse plane slightly proximal to the hip joint along the pelvic bone (Fig. 2). For lateral snap, the dynamic evaluation was made during flexion and extension of the hip as the patient was lying on the contralateral hip, with the transducer in the transverse plane over the greater trochanter. Information about whether pain was associated with the snapping hip was obtained by directly questioning the patient during the sonographic examination. This information was binary: presence or absence of pain. Results Two patients examined were excluded from the data analysis. Clinical information on painful symptoms was incomplete for one patient when reviewing the cases, and another patient could not reproduce the hip snap at the time of the sonographic study (Table 1). In the analyzed hips of the other 18 patients (n = 36), the conventional sonographic examinations enabled identification of the hyperechogenic iliopsoas tendon surrounded by hypoechogenic muscle, and the tendon s relationship with the coxofemoral joint. The hyperechogenic iliopsoas tendon has a slightly oval shape on a transverse image, and a fibrillar appearance is noted on a longitudinal section (Fig. 3). The iliotibial band is seen on sonography as hyperechogenic tissue just superficial to the greater trochanter. Signs of iliopsoas tendinopathy (thickened, heterogeneous, or hypoechogenic tendon) (n = 6) (Fig. 4), iliopsoas bursitis (thickened bursa) (n = 1), rectus femori tendinopathy (thickened tendon) (n = 2), iliotibial band tendinopathy (thickened band) (n = 1), or synovitis (thickened synovial membrane) (n = 1) were identified on conventional examinations. Six hips had no structural abnormalities of these tendons, but pain was elicited by pressure with the sonographic transducer on the iliopsoas tendon (n = 2), rectus femori tendon (n = 3), and gluteus maximus tendon (n = 1). Of the 36 hips analyzed, 26 cases of snapping hip were identified on dynamic sonographic evaluations. The cause of the snap could be identified in 24 of the 26 cases. Twenty-two snapping hips were caused by an abnormal motion of the iliopsoas tendon. In a normal hip, during joint motion the tendon glides smoothly over the pelvic bone from side to side on a transverse plane (Fig. 5). In the case of a snapping iliopsoas tendon, this tendon suddenly displays an abrupt abnormal displacement (lateromedial or Fig. 2. Diagram illustrating pathomechanics of snapping iliopsoas tendon., s hip is flexed, abducted, and externally rotated, iliopsoas tendon moves laterally with regard to iliopectineal eminence. Transducer may be placed either on transverse over hip joint () or oblique transverse over pelvic rim () to accommodate movement of hip., When hip is moved back toward complete extension, tendon impinges on iliopectineal eminence. s extension continues, tendon at some point is released from impingement, moving abruptly medially. This abrupt abnormal tendon motion is characteristic of snapping hip. 68 JR:176, January 2001

3 Sonography of Snapping Hip TLE 1 Results of Conventional and Dynamic Sonography Showing Type of Snapping Hip and Presence or bsence of Pain Patient Conventional Sonography Dynamic Sonography: Snapping Hip Sex ge (yr) Right Left Right Left F 14 Rectus femori tendon (S) Iliopsoas tendon (+) F 31 Iliopsoas tendon (T) Iliopsoas tendon (+) F 13 Rectus femori tendon (T) Iliopsoas tendon ( ) Iliopsoas tendon ( ) F 13 Rectus femori tendon (S) Iliopsoas tendon ( ) Iliopsoas tendon ( ) F 39 Synovial membrane (T) Iliopsoas tendon ( ) Iliopsoas tendon ( ) F 12 Iliopsoas tendon (T) (hypo) Iliopsoas tendon ( ) Iliopsoas tendon (+) Rectus femori tendon (S) F 23 Iliopsoas tendon (+) F 15 Iliopsoas tendon (+) Iliopsoas tendon (+) F 18 Iliopsoas tendon (T) Iliopsoas tendon (+) Iliopsoas tendon (+) Iliopsoas bursa (T) F 13 Iliopsoas tendon (T) Iliopsoas tendon (+) Iliopsoas tendon ( ) F 27 Gluteus maximus (S) Iliopsoas tendon ( ) F 18 Iliopsoas tendon (T) Iliopsoas tendon (+) F 32 Iliopsoas tendon (hetero) Iliopsoas tendon (+) M 33 Iliopsoas tendon (+) M 31 Iliopsoas tendon ( ) M 36 Iliotibial band (T) Iliotibial band (+) Iliotibial band (+) F 14 Iliopsoas tendon (S) Iliopsoas tendon (S) Undetermined ( ) Undetermined ( ) F 16 Rectus femori tendon (T) Not documented ( ) Not documented ( ) F 27 Iliopsoas tendon (T) Incomplete data F 17 Snapping not reproduced Note. F = female; M = male; S = sensitivity; T = thickened; (+) = painful snapping hip; ( ) = painless snapping hip; hetero = heterogeneous; hypo = hypoechogenic. Fig year-old woman with asymptomatic normal right hip. and, Transverse () and longitudinal () sonograms show hyperechogenic iliopsoas tendon (arrows) and hyperechogenic margins of acetabulum () and femoral head (F). Note overlying hypoechogenic cartilage (c). lso note fibrillary appearance of iliopsoas tendon on. mediolateral) during hip motion (Figs. 2 and 6). Occasionally, this abrupt tendon jerk was associated with a change in the shape of the tendon. Hip movements that reproduced the snapping iliopsoas tendon were from flexion, abduction, and external rotation to extension (n = 10); from extension to flexion, abduction, and external rotation (n = 5); from extension to flexion, abduction, external rotation, and back to extension (n = 2); from flexion to extension (n = 4); and from extension to flexion with internal rotation (n = 1). Two cases of snapping hip were caused by the iliotibial band friction over the greater trochanter. n abrupt posterior movement of the JR:176, January

4 Pelsser et al. Fig year-old girl with iliopsoas tendinopathy of left hip. Split image with transverse sonograms of right (on left) and left (on right) hips. Left iliopsoas tendon (right arrow) is hypoechogenic compared with normal right hyperechogenic iliopsoas tendon (left arrow). = acetabulum; F = femoral head. iliotibial band was observed on sonography when the flexed hip was extended (Fig. 7). The cause of two snapping hips could not be clearly identified on sonography. The motion of both iliopsoas tendons was normal, but an abnormal tissue displacement was observed anterior to the coxofemoral joint and medial to the iliopsoas tendon when the hip was externally rotated. Presumably, this was an iliofemoral ligament moving abnormally. In two hips, sonographic evaluation could not enable objective identification of any abnormal motion of the soft tissues surrounding the hip even though the patient was reporting a subjective snapping sensation. The sonographer was able to establish a temporal correlation between the abnormal motion of the structure coinciding with a click felt by the examiner s hand through the transducer and the painful hip snap reported by the patient. The pain was felt by the patient at the exact moment the tendon was snapping on sonography. Painless snaps were also felt through the transducer by the examiner. Fifty percent of the snapping hips (12 snapping iliopsoas tendons and 2 snapping iliotibial bands) were painful. ll of the normal nonsnapping hips (n = 8) showed smooth mediolateral tendon motion during hip movement without abnormal tendon jerk. Discussion Snapping hip is described as a painful and audible snap of the hip felt with motion. This syndrome has a wide variety of causes of intraarticular or of extraarticular origin. Intraarticular snapping hip has been attributed to synovial osteochondromatosis, loose bodies, acetabular labral tears, osteochondral fractures, and transient subluxation of the femoral head [18 20]. Extraarticular snapping hip can be caused by friction of the iliotibial band [3, 4] or gluteus maximus [20] over the greater trochanter, by the iliofemoral ligament snapping over the femoral head [14], or by the iliopsoas tendon impinging on an osseous prominence [5 7]. Fig year-old woman with normal iliopsoas tendon motion., Transverse sonogram of right hip shows normal, oval-shaped, hyperechogenic iliopsoas tendon anterior to acetabulum () and femoral head (F). s hip is flexed, abducted, and externally rotated, iliopsoas tendon moves laterally in direction indicated by arrow. Lateral displacement of tendon is smooth with mild rotatory motion (counterclockwise for right hip)., s hip is moved back to complete extension, iliopsoas tendon smoothly glides back medially in direction shown by arrow. There is mild rotatory motion of tendon (clockwise for right hip). = acetabulum; F = femoral head. 70 JR:176, January 2001

5 Sonography of Snapping Hip From a clinical standpoint, snapping hip becomes a diagnostic possibility when the patient reports a click or a snap in the hip with motion. On physical examination, the clinician may either hear the click, feel the snap through his hand, or actually feel a band of tissue passing abruptly under his hand. Fig year-old girl with right snapping iliopsoas tendon. and, Oblique transverse sonograms just above coxofemoral joint during video recording of right hip motion show changes in iliopsoas tendon after snapping has occurred. Iliopsoas tendon (straight arrow) is anterior to pelvic bone (curved arrows). Flexed and abducted hip is moved toward extension and rotated from external position () to more internal position (). During motion, tendon suddenly displays abrupt abnormal displacement getting suddenly closer to pelvic bone and change in its shape (from round in to ovoid in ), which are correlated with painful snap felt by patient. Fig year-old man with snapping iliotibial band of left hip. and, Transverse sonograms at level of left greater trochanter (T) as patient is lying on right side. When hip is flexed (), iliotibial band (arrows) presents as stripe overlying trochanter. During extension of hip (), abrupt displacement of iliotibial band (arrows) occurs as it gets closer to trochanter and coincides with snap. Classically, when a snapping iliopsoas tendon was suspected, bursography or tenography could be performed as preoperative procedures to confirm the diagnosis [7 9]. Recently, sonography has been used in the diagnosis of this entity [10 12]. Sonographic studies are advantageous when compared with bursography and tenography because they allow direct noninvasive real-time visualization of soft tissues surrounding the coxofemoral joint in a single examination. ecause sonography cannot allow evaluation of the intraarticular space, radiography, arthrography, CT, or MR imaging may still be JR:176, January

6 Pelsser et al. required to confirm the diagnosis of an intraarticular cause of snapping hip [10]. For painful snapping hip, conservative treatment such as rest, stretching exercises, or oral antiinflammatory drugs are often sufficient to alleviate the symptoms [21]. Steroid injection represents another alternative [7]. In refractory cases, surgical lengthening can be performed [21]. The conventional sonographic study of the hip is an important part of the examination because it can allow identification of structural abnormalities. Sonographic findings of tendinitis, bursitis, synovitis, or local tenderness over the course of a tendon, for example, may orient the clinician toward the appropriate diagnosis. There are no normal thickness values established for the tendons around the hip in the literature. ased on the premise that these structures are symmetric on the left and right sides of a given patient, structural abnormality was suspected when corresponding tissues were asymmetric or when they had an abnormal echogenicity. Dynamic sonographic evaluations allowed identification of an abnormal displacement of the iliopsoas tendon with or without dynamic change in its shape in 22 hips. These findings are similar to those described by Janzen et al. [12] who reported a distinct momentary mediolateral or rotatory motion of the iliopsoas tendon. Sonographic signs of tendinopathy are not a common feature; only six of 22 hips with a snapping iliopsoas tendon showed such abnormality in our study. Similarly, in the series of Janzen et al. sonography revealed a thickened tendon in only two of eight snapping iliopsoas tendons. lso, iliopsoas bursitis does not seem to be an essential feature of the syndrome as thought by other researchers [22]. In fact, only one of 22 snapping iliopsoas tendons was associated with a thickened iliopsoas bursa in our study. In another study [7], six of eight snapping hips were not associated with bursal fluid. In our study, no definite correlation was found between the findings of the conventional static sonographic studies and the presence of snapping hip. The bony landmarks on which the iliopsoas tendon may impinge are several: the iliopectineal eminence, the anteroinferior iliac spine, or an osseous ridge on the lesser trochanter [7]. ecause the location of the mechanical restraint cannot be clearly delineated on sonography during hip movement, iliopsoas bursography or tenography [7 9] or CT [9 15] may still be indicated as complementary examinations to determine the exact location of the impingement. Sonography also allowed diagnosis of two iliotibial bands snapping over the greater trochanter. This entity, described in the orthopedic literature [3, 13, 16], has never to our knowledge been imaged or described in the radiology literature. In the two cases of snapping hip in which the cause could not be precisely identified, considering the anatomic location of the snapping structure (see Results), it was hypothesized that the iliofemoral ligament was impinging over the femoral head, a potential cause of snapping hip mentioned by Howse [14]. Snapping hip in both hips of one patient, not documented on sonography but subjectively present according to the patient, may have represented false-negative outcomes or may have had an intraarticular origin. This patient is a good example of a case in which the investigation could have been pursued further with CT or MR imaging. However, because the patient had no pain associated with snapping hip, additional higher cost testing was not performed. The most commonly recognized movement of the hip that reproduces the snap is extension of the flexed abducted and externally rotated hip. Dynamic studies to evaluate a snapping iliopsoas tendon should not be limited to only that movement because, in some patients of our study, other movements were needed to elicit the snap. The patients examined in our study were able to reproduce the hip snap in the recumbent position, with snapping iliopsoas tendons observed in the supine position and the snapping iliotibial band seen in the lateral position. lthough this was not necessary in our study, there might be instances when the patient would better or only reproduce the hip snap when standing up. This might especially be the case for snapping iliotibial band for which weight-bearing and contraction of the gluteus muscle might be important to generate the hip snap. It is known from the orthopedic literature that iliotibial band or gluteus muscle snap may not be reproduced with mobilization of the hip when the patient is under general anesthesia unless the gluteus muscle is electrically stimulated [2, 13]. Sonography is a modality well suited for dynamic examination of patients as they are standing up, if weight-bearing is needed to observe the abnormality. Even though bilateral snapping hip was reported to be rare by Dickinson [13], our data suggest that it is relatively common, occurring in 56% of our patients. lso, in our study the most frequent cause of bilateral snapping hip was an abrupt displacement of the iliopsoas tendon (79%). This is in contrast with the literature, which indicates that the iliotibial band is the most frequent cause [5]. This may represent a selection bias in our study. Patients with snapping iliotibial band, which is more easily diagnosed clinically than a snapping iliopsoas tendon, may be less often referred to a radiologist for investigation, thus contributing to the under representation of patients with snapping iliotibial band in our study. Further studies would be required to precisely determine the relative prevalence of snapping iliotibial bands and snapping iliopsoas tendons. In cases in which the patient cannot reproduce or can reproduce only intermittently the snap during sonographic evaluation, sonography may not identify the underlying cause of the snap (as in one of our patients). Other researchers [6, 13 15] have mentioned that snapping hip could occur in patients without pain, but they have not reported such asymptomatic patients. Nunziata and lumenfeld [1], who in 1951 were the first to describe a snapping iliopsoas tendon, reported a case of a patient clinically diagnosed with this condition who had no pain and who refused to undergo surgical exploration. innie [16], in 1913, also reported one patient with bilateral painless snapping hips caused by the gluteus maximus. In his review of the literature, innie estimated that 12 of 41 patients previously reported with snapping hip had no disability [16]. It is probable that the number of cases of asymptomatic snapping hip is underestimated in the literature because patients without pain would not seek medical attention. In our study, sonography enabled us not only to identify the cause of the snap but also to establish an immediate temporal correlation between the abnormal tendon motion and the generation of painful symptoms. Fourteen cases of snapping hip (50%) were painful, and the other half of the cases were painless. It is important to establish this correlation because the pain may originate from conditions other than extraarticular snapping hip, which may be painless. fter the exact origin of the symptoms has been identified, appropriate treatment can be offered to the patient. ilateral snapping hip can be bilaterally painful, bilaterally painless, or painful in one hip and painless in the other. Our data confirm 72 JR:176, January 2001

7 Sonography of Snapping Hip that snapping hip can be painless. We suggest that the term snapping hip syndrome be used for painful snapping hip only. The term snapping hip could simply refer to the painless condition. We believe that sonographic investigation of snapping hip may not be needed if the diagnosis is clinically obvious. However, sonography should be performed when clinical diagnosis is uncertain because an extraarticular cause can be mistaken for an intraarticular one. Other imaging modalities such as CT or MR imaging could be used when sonographic findings are negative. In conclusion, we believe that sonography should be the first imaging modality used to evaluate snapping hip. Conventional sonographic evaluations can reveal signs of tendinitis, bursitis, or synovitis. Dynamic sonographic studies can help to identify the structure involved in extraarticular snapping hip by showing the abnormal displacement of this structure with hip motion. This study also shows that snapping hips can be painless, which emphasizes the need to establish a temporal correlation with sonography between the abnormal motion of the structure and the presence or absence of pain. References 1. Nunziata, lumenfeld I. Cadera a resorte: a proposito de una variedad. Prensa Med rgent 1951;32: Jones FW. The anatomy of snapping hip. J Orthop Surg 1920;2: Mayer L. Snapping hip. Surg Gynecol Obstet 1919;29: rignall CG, Stainsby GD. The snapping hip: treatment by Z-plasty. J one Joint Surg r 1991;73-: eals RK. Painful snapping hip in young adults. West J Med 1993;159: Lyons JC, Peterson LF. The snapping iliopsoas tendon. Mayo Clin Proc 1984;59: Schaberg JE, Harper MC, llen WC. The snapping hip syndrome. m J Sports Med 1984;12: Vaccaro JP, Sauser DD, eals RK. Iliopsoas bursa imaging: efficacy in depicting abnormal iliopsoas tendon motion in patients with internal snapping hip syndrome. Radiology 1995;197: Staple TW, Jung D, Mork. Snapping tendon syndrome: hip tenography with fluoroscopic monitoring. Radiology 1988;166: Cardinal É, uckwalter K, Capello WN, Duval N. US of the snapping iliopsoas tendon. Radiology 1996;198: Hashimoto E, Green TM, Wiitala L. Ultrasonographic diagnosis of hip snapping related to iliopsoas tendon. J Ultrasound Med 1997;16: Janzen DL, Partridge E, Logan M, Connell DG, Duncan CP. The snapping hip: clinical and imaging findings in transient subluxation of the iliopsoas tendon. Can ssoc Radiol J 1996;47: Dickinson M. Case reports by Dr. rthur M. Dickinson: bilateral snapping hip. m J Surg 1929;6: Howse JG. Orthopaedists aid ballet. Clin Orthop 1972;89: Silver SF, Connell DG, Duncan CP. Case report 550: snapping right iliopsoas tendon. Skeletal Radiol 1989;18: innie JF. Snapping hip (hanche à resort; schnellende hufte). nn Surg 1913;58: Cardinal É, Chhem RK, ubin. dult hip. In: Chhem RK, Cardinal É, eds. Guidelines and gamuts in musculoskeletal ultrasound. New York: Wiley-Liss, 1999: Campbell JD, Ryan J, Feagin J Jr. Injuries of the pelvis, hip and thigh. In: Grana W, Kalenak, eds. Clinical sports medicine. Philadelphia: Saunders, 1991: Walker J, Rang M. Habitual hip dislocation in a child: another cause of snapping hip. Clin Pediatr 1992;31: rignall CG, rown RM, Stainsby GD. Fibrosis of the gluteus maximus as a cause of snapping hip. J one Joint Surg m 1993;75-: Jacobson T, llen WC. Surgical correction of the snapping iliopsoas tendon. m J Sports Med 1990;18: Johnston CM, Wiley JP, Lindsay DM, Wiseman D. Iliopsoas bursitis and tendinitis. Sports Med 1998;25: JR:176, January