Sonography of the Acetabular Labrum

Transcription

1 Case Series Visualization of Labral Injuries During Intra-Articular Injections Carolyn M. Sofka, MD, Ronald S. Adler, PhD, MD, Martha A. Danon, MD Objective. The purpose of this series was to describe the improved conspicuity in the sonographic appearance of acetabular labral injuries during routine sonographically guided intra-articular injections. Methods. Sonographic examinations of patients undergoing routine sonographically guided intraarticular hip injections were reviewed for evidence of labral injuries (n = 21). Sonographic examinations were then correlated with magnetic resonance images of the ipsilateral hip when available (n = 14). Results. Before injection, 13 acetabular labra had linear or irregular hypoechoic clefts or fissures through the normally hyperechoic fibrocartilaginous labrum, thought to represent tears. Eight of the labra showed a more globular alteration in morphologic characteristics, with diffuse thickening and irregularity. During intra-articular injection, the visualized injected fluid outlined the labrum, yielding a sonoarthrographic effect, providing a fluid interface along the labral boundaries, and confirming the presence of a tear by imbibition of injected material into the defect with a resultant subjective improvement in the labral injury. Conclusions. Evaluating the labrum after injection may improve visualization of labral injuries, as a result of greater labral conspicuity. Key words: hip; intra-articular injections; labrum; sonography. Abbreviations MR, magnetic resonance Received February 7, 2006, from the Department of Radiology and Imaging, Hospital for Special Surgery, New York, New York USA. Revision requested March 12, Revised manuscript accepted for publication May 4, Address correspondence to Carolyn M. Sofka, MD, Department of Radiology and Imaging, Hospital for Special Surgery, 535 E 70th St, New York, NY USA. sofkac@hss.edu Acetabular labral tears are common causes of hip pain. Symptoms can be nonfocal, with patients having general hip and groin region pain. 1 Given the often-confusing clinical picture, patients are often referred for imaging confirmation of a labral tear before arthroscopic treatment. The diagnosis of an acetabular labral tear is generally made with magnetic resonance (MR) imaging, either with noncontrast high-resolution MR imaging of the hip using dedicated surface coils or MR arthrography. 2 4 Magnetic resonance imaging is not an option for all patients because of either relative or absolute contraindications, as well as the relatively high cost by the American Institute of Ultrasound in Medicine J Ultrasound Med 2006; 25: /06/$3.50

2 The sonographic appearance of the glenoid labrum has been described in a cadaveric model as a compact, hyperechoic, triangular structure with irregular hypoechoic clefts seen in the setting of a tear. 5 Given the similar histologic structure of the fibrocartilaginous glenoid labrum and acetabular labrum and the similar signal and morphologic characteristics used to define the integrity of both structures on MR imaging, the normal and pathologic appearances of the acetabular labrum at sonographic evaluation can be extrapolated. 6,7 We report the appearance of the acetabular labrum in patients undergoing routine sonographically guided intra-articular injections and the morphologic changes of the acetabular labrum that can occur during routine intra-articular injections. Materials and Methods This study received approval from our institution s Institutional Review Board. Sonographic examinations were performed over a 9-month period, from July 2004 through February Our sonographic database was reviewed, and all hip injection reports describing labral injuries were reviewed, with these cases cross-referenced to search for those who had MR studies of the hip additionally, and the MR reports were reviewed. Patients were referred for sonographically guided therapeutic hip injections for hip pain. Examinations were performed on either a Sonoline Elegra system (Siemens Medical Solutions, Mountain View, CA) or an iu22 system (Philips Medical Systems, Andover, MA). The examinations on the Siemens machine were, in general, performed with a 7.5-MHz linear transducer, whereas the examinations on the Philips machine were performed with a linear 8-4 or 12-5 MHz or a curved 9-4 MHz transducer, dependent on the patient s body habitus. Procedures were performed by a musculoskeletal radiologist trained in musculoskeletal sonography with the assistance of either a musculoskeletal radiology fellow or sonographer. 8 For sonographically guided intra-articular therapeutic injections at our institution, a 22-gauge spinal needle is typically used. The patient is placed supine, and the hip joint is visualized from a longitudinal approach with the junction of the femoral head and neck identified, the target point for needle placement. The hip region is cleansed using a routine sterile technique, and 1% lidocaine (Abbot Laboratories, North Chicago, IL) is used for local anesthesia. The spinal needle is advanced into the hip joint under sonographic guidance, until the joint is entered, and the needle tip is on the cortical bone (Figure 1). The amount and composition of fluid injection are often dependent on the referring clinician, with the typical composition consisting of 1% lidocaine (Abbot Laboratories), 0.5% bupivacaine (Sensorcaine; Astra Pharmaceuticals, Westborough, MA), and triamcinolone (Kenalog, 40 mg/ml; Apothecon, Princeton, NJ). Results There were 21 patients (21 hips; 8 male and 13 female). There were 8 left hips and 13 right hips. Patient ages ranged between 17 and 73 years. Fourteen patients had MR correlation with noncontrast high-resolution MR imaging of the hip performed at our institution, and 1 case had outside MR imaging available for comparison. Noncontrast high-resolution MR imaging of the hip using dedicated surface coils has been validated with arthroscopic correlation for diagnosing an acetabular labral tear. 2 The MR examinations were performed between July 2004 and January 2005 between the same day as and 9 months after the sonographic examinations, with 1 outlier MR examination being performed 7 years previously (average time between MR examination and sonographic procedure was 1.8 months). Figure 1. Longitudinal sonogram showing the technique used for intra-articular injection. The needle (arrow) enters the hip joint from an anterior, longitudinal approach J Ultrasound Med 2006; 25:

3 Sofka et al Table 1. Sonographic Findings During Intra-Articular Injections Patient Age Sex Side Sonographic Findings 1 54 Male Right Degenerated anterior labrum with ganglion cyst formation 2 49 Male Left Anterior labral tear, minimal degenerative osteophyte formation 3 20 Male Right Anterior labral tear 4 62 Female Right Degeneration of the anterior labrum with multiple fissures 5 44 Female Right Marked degeneration of the anterior labrum with osteophytes 6 28 Female Right Anterior labral tear 7 50 Female Right Degeneration of the anterior labrum 8 56 Male Left Degeneration of the anterior labrum with osteophytes 9 41 Male Right Anterior labral tear Male Right Anterior labral tear Female Right Degeneration of the anterior labrum Female Left Anterior labral tear Female Right Anterior labral tear Female Left Anterior labral tear Female Right Anterior labral tear Female Left Anterior labral tear Male Left Anterior labral tear Female Left Degenerative anterior labral tear Female Right Degeneration of the anterior labrum Female Left Anterior labral tear Male Right Degenerative tear of the anterior labrum Sonographic and MR reports were reviewed for descriptions of labral injuries. There was concordance between the sonographic findings and the MR reports with regard to descriptions of labral injuries (eg, tear and degeneration). There were 13 anterior labral tears seen during sonographic evaluation of the hip, similar to the MR examinations (Table 1). Acetabular labral tears are seen as irregular or linear hypoechoic clefts through the normally hyperechoic fibrocartilage of the anterior acetabular labrum (Figures 2 5). In all cases of tears, fluid filled the defect confirming the tear, similar to that observed during conventional or MR arthrography. There were 8 cases of pure labral degeneration without visualization of a discrete tear, with truncation, inhomogeneity, and fraying of the anterior labrum. One example of a labral tear from our series is shown in Figure 3. In the absence of intraarticular fluid and air bubbles, a labral tear can sometimes be difficult to see, occasionally blending with the overall decreased echogenicity of a degenerated labrum. During therapeutic steroid injection, the echogenic microbubbles and fluid in the hip track through the tear in the anterior labrum, making it more conspicuous (Figure 3A). This case had direct MR correlation, which also showed the tear (Figure 3B). Another example shows the advantage of fluid in the hip outlining the morphologic characteristics of the anterior labrum. In this 42-year-old female patient who had a chronic degenerated labral tear with a blunted free edge, as shown on the MR examination (Figure 5B), the injected fluid in the hip clearly outlines the morphologic characteristics of the anterior labrum (Figure 5A). In the absence of intra-articular fluid, a blunted, truncated labrum may blend with the echogenic anterior capsule, remaining more difficult to evaluate. Figure 2. Longitudinal sonogram during intra-articular injection showing echogenic microbubbles distributed along the nondependent portion of the hip joint (over the femoral head; thin arrow) and hypoechoic fluid coursing through a mildly distracted tear of the anterior labrum (thick arrow). J Ultrasound Med 2006; 25:

4 A B Figure 3. Anterior labral tear in a 50-year-old female patient. A, Longitudinal sonogram of the hip during intra-articular injection showing echogenic microbubbles and fluid in the hip, with fluid tracking through the tear in the anterior labrum (arrow). B, Sagittal high-resolution proton density fast spin echo surface coil MR image of the same patient showing the tear at the base of the anterior labrum (arrow). Discussion Acetabular labral tears are common causes of hip pain, especially in the young athletic population. Cadaveric studies have shown that 88% of hips examined in patients older than 30 years had traumatic labral injuries. 7,9 Traumatic labral tears are usually in the anterosuperior quadrant and can occur in sports resulting in sudden twisting or pivoting motions. 7,10 Labral tears can predispose patients to early osteoarthritis and can occur in conjunction with additional chondral injuries. 7,10 Diagnosis of a labral tear can be a clinical dilemma because patients may have a confusing clinical picture, often with nonfocal clinical signs and symptoms such as vague groin pain. 1 Hip or groin pain or, more specifically, pain with flexion, can occur with both intra-articular as well as periarticular conditions, such as iliopsoas tendinitis; therefore, patients are often referred for diagnostic imaging of the hip for further evaluation. Early diagnosis of acetabular labral tears is important, especially in the young athlete, because these can be treated with arthroscopy, thereby ideally curbing progression to early osteoarthritis. 11 Figure 4. Chronically torn anterior labrum in a 45-year-old female patient. A, Longitudinal sonogram during intra-articular injection showing hypoechoic fluid coursing through an irregular split of the anterior labrum (arrow). B, Sagittal high-resolution proton density fast spin echo surface coil MR image of the same patient showing degeneration of the labrum with an irregular tear at the base (arrow). Note associated degenerative changes in the hip with anterior osteophytes at the anterior margin of the acetabulum. A B 1324 J Ultrasound Med 2006; 25:

5 Sofka et al A Figure 5. Anterior labral tear in a 42-year-old female patient. A, Longitudinal sonogram during intra-articular injection showing hypoechoic fluid in the joint outlining the torn, truncated anterior labrum (arrow). B, Sagittal high-resolution proton density fast spin echo surface coil MR image of the same patient showing the torn anterior labrum (arrow). B The anterior acetabular labrum can generally be visualized in the longitudinal projection, producing an image similar to a sagittal MR image (Figures 3 5). Normally, the acetabular labrum is seen as a hyperechoic, compact, triangular structure because of its composition of fibrocartilage. Tears of the acetabular labrum are seen as irregular or linear hypoechoic fissures or clefts through the anterior labrum. Associated periarticular fluid collections (ganglion cysts) can also be readily evaluated with sonography. During routine sonographically guided intra-articular injections, the injected hypoechoic fluid mixture, often containing echogenic microbubbles, can be visualized, thus helping confirming accurate intra-articular needle placement (Figure 2). 12 During intra-articular hip injections, the injected fluid with echogenic microbubbles can be seen tracking over the anterior margin of the femoral head, outlining the articular cartilage, and filling the hypoechoic tear in the labrum, yielding a sonoarthrographic effect and often making them more conspicuous (Figure 2). Limitations to our study include the lack of arthroscopic confirmation for the presence of acetabular labral tears, although we used noncontrast high-resolution MR imaging with dedicated surface coils as our reference standard because this has been validated with arthroscopy, albeit these images were only available in 67% of cases. 2 In addition, all patients in our series had hip pain and a high pretest probability of labral injuries, either traumatic or degenerative, because they were referred for therapeutic injections, although statistical analysis determining the accuracy and sensitivity of sonography was not an objective of this descriptive study. Detailed morphologic classification of labral injuries was not made, with the labral injuries simply divided into tear and degeneration, with degenerative tears included in the general labral tear category. Anecdotally, injected fluid and echogenic microbubbles do not always extend superiorly to fill a labral tear if present, although this is usually uncommon; this likely has to do with the physiologic characteristics of the hip joint and contour of the femoral head, as well as the presence of preprocedure viscous synovial fluid and synovitis in the hip. In conclusion, sonography can define labral morphologic characteristics in patients with suspected hip injuries. We have noted a subjective improvement in visualization of labral morphologic characteristics after sonographically guided intra-articular injection. Fluid dissecting through the acetabular labrum after injection through a defect may be considered confirmation of a tear, similar to that observed during conventional or MR arthrography. References 1. Narvani AA, Tsiridis E, Kendall S, Chaudhuri R, Thomas P. A preliminary report on prevalence of acetabular labrum tears in sports medicine patients with groin pain. Knee Surg Sports Traumatol Arthrosc 2003; 11: Mintz DN, Hooper T, Connell D, Buly R, Padgett DE, Potter HG. Magnetic resonance imaging of the hip: detection of J Ultrasound Med 2006; 25:

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