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1
Department of Diagnostic Radiology, CHUM-St-Luc Hospital, 1058 Saint-Denis
St., Montreal, Quebec, H2X 3J4 Canada.
2
Department of Family Medicine, University of Montreal, 3590, Ontario St. East,
Rm. 102, Montreal, Quebec, H1W 1R7 Canada.
Received September 22, 1999;
accepted after revision June 8, 2000.
Address correspondence to É. Cardinal.
Abstract
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MATERIALS AND 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.
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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, 13,14,15,16]. 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.
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Sonographic studies were performed by one experienced musculoskeletal radiologist using a curved 5.0-MHz or a linear 7.0-MHz transducer (128-XP; Acuson, Mountain View, CA). 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. 2A,2B). 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.
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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.
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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. 3A,3B). 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).
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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. 5A,5B). In the case of a snapping iliopsoas tendon, this tendon suddenly displays an abrupt abnormal displacement (lateromedial or mediolateral) during hip motion (Figs. 2A,2B and 6A,6B). 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).
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Two cases of snapping hip were caused by the iliotibial band friction over the greater trochanter. An abrupt posterior movement of the iliotibial band was observed on sonography when the flexed hip was extended (Fig. 7A,7B).
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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. All of the normal nonsnapping hips (n = 8) showed smooth mediolateral tendon motion during hip movement without abnormal tendon jerk.
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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. Classically, when a snapping iliopsoas tendon was suspected, bursography or tenography could be performed as preoperative procedures to confirm the diagnosis [7,8,9]. Recently, sonography has been used in the diagnosis of this entity [10,11,12]. 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. Because sonography cannot allow evaluation of the intraarticular space, radiography, arthrography, CT, or MR imaging may still be 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. Based 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. Also, 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]. Because the location of the mechanical restraint cannot be clearly delineated on sonography during hip movement, iliopsoas bursography or tenography [7,8,9] or CT [9,10,11,12,13,14,15] 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. Although 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. Also, 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, 13,14,15] have mentioned that snapping hip could occur in patients without pain, but they have not reported such asymptomatic patients. Nunziata and Blumenfeld [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. Binnie [16], in 1913, also reported one patient with bilateral painless snapping hips caused by the gluteus maximus. In his review of the literature, Binnie 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. After the exact origin of the symptoms has been identified, appropriate treatment can be offered to the patient. Bilateral snapping hip can be bilaterally painful, bilaterally painless, or painful in one hip and painless in the other. Our data confirm 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.
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