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Original Report |
1 Both authors: Department of Radiology and Imaging, Hospital for Special Surgery, 535 E. 70th St., New York, NY 10021.
Received April 8, 2002;
accepted after revision September 10, 2002.
Address correspondence to C. M. Sofka.
Abstract
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CONCLUSION. We found sonography to be a useful method of imaging the rotator cuff after arthroplasty. Extended field-of-view imaging and tissue harmonic imaging aided in diagnosis by improving visualization of regional anatomic landmarks and increasing conspicuity of small tendon tears.
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The accuracy of sonography for the diagnosis of rotator cuff tears has been shown [3]. However, sonography of the postoperative shoulder has not been extensively studied. The presence of a joint replacement presents a unique situation for sonography. Often, the patient has a limited range of motion, especially if an acute tendon tear is present or if a moderate postoperative scar has formed. Altered regional anatomy of the shoulder and artifact from the metallic components must also be considered when examining the shoulder of a patient who has undergone arthroplasty.
We reviewed our experience with shoulder sonography in the presence of a joint replacement for qualitative evaluation of the periprosthetic soft tissues.
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Sonographic images were obtained on an Elegra unit (Siemens Medical, Mountain View, CA) usually using a medium-frequency (i.e., 7.5-MHz) linear transducer operating in the phase-inversion tissue harmonics mode. Sonography was performed with the patients in the standard sonographic positions to sequentially evaluate the biceps tendon, the subscapularis tendon, the teres minor muscle and tendon, and the infraspinatus and supraspinatus tendons.
The quality of the regional musculature was evaluated on sonography. Atrophy was seen at sonography as diffuse increased echogenicity throughout the muscle, often with decreased muscle bulk and thinning of the muscle. The presence of any periprosthetic fluid collection was noted.
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In all patients, the prosthesis itself did not hinder examination of the rotator cuff. The metallic components of the prosthesis appear as a linear echogenic interface with moderate posterior reverberation artifact, similar to that observed during the routine interventional procedures using a sonographically guided needle (Figs. 2 and 3A, 3B). The polyethylene liner can be identified as a linear echogenic interface with posterior acoustic shadowing.
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A cadaveric study defining the typical sonographic appearance of joint arthroplasty was performed using total-knee replacement as a model [6]. In that study, a characteristic metal–bone–polyethylene interface was described, with metal having a strong linear echogenic interface and strong posterior reverberation artifact. The polyethylene liner was depicted on sonography as an echogenic interface with an anechoic posterior border [6].
Postoperative rotator cuff tear is the second most frequent complication of shoulder replacement [1]. The failure of subscapularis tendon repair or a retear is one of the most consistently implicated factors in the development of anterior instability after shoulder replacement [7]. In our series, we had several patients with rotator cuff tears, including one patient with a massive subscapularis tendon tear (Fig. 3A, 3B).
A reasonable understanding of the regional anatomy and knowledge of the characteristic appearance of the metal prosthesis are necessary for diagnostic accuracy. We found that extended field-of-view imaging allows a panoramic image to be created, thus yielding a global picture of the regional anatomy [8]. With extended field-of-view imaging, the motion of the probe over a single sweep of the transducer is tracked, and an image is constructed [9]. We routinely use extended field-of-view imaging to produce images of all the tendons of the rotator cuff, from the muscle–tendon junction to the bony insertion (Figs. 2 and 3A, 3B). Not only does extended field-of-view imaging provide more anatomic information than conventional sonographic images, but extended field-of-view imaging also provides an image that provides a global perspective for the referring clinician to review. Extended field-of-view imaging enables one to recognize the bony landmarks (i.e., acromion, humeral component, greater tuberosity) as well as the soft-tissue interfaces on a single image.
As with other authors [10], we found that tissue harmonic imaging greatly increased the conspicuity of soft-tissue abnormalities; small rotator cuff tears were subjectively more visible (Fig. 7A, 7B) on tissue harmonic images than on conventional sonographic images. Patients with shoulder replacements often experience moderate to severe regional muscle atrophy, most commonly affecting the deltoid and the teres minor muscles. Atrophy can limit evaluation of the periprosthetic soft tissues because the normal appearance of muscles and tendons is altered on gray-scale sonography. If muscle atrophy is diffuse, the muscle appears completely echogenic (Fig. 5). Therefore, diagnosing chronic rotator cuff deficiency, in which fluid may or may not be present in the subdeltoid bursa, can be difficult. In this situation, echogenic deltoid muscle would be apposed to echogenic subdeltoid fat and the echogenic humeral head. By increasing the contrast of the adjacent interfaces using tissue harmonic imaging combined with extended field-of-view imaging, one can increase diagnostic accuracy by more clearly identifying these individual structures even when muscular atrophy is present.
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The value of power Doppler sonography in revealing the musculoskeletal system has been previously described [11, 12]. We routinely use power Doppler sonography in most of the sonographic examinations of the musculoskeletal system, including the postoperative shoulder (Fig. 4). Because focal areas of inflammation can be seen on power Doppler sonography, the clinician can identify the abnormalities that are most acute in patients in whom more than one finding is evident.
In conclusion, we found that sonography is a rapid and reliable method to use for evaluating the periprosthetic soft tissues, including the rotator cuff, in patients who have undergone shoulder replacement. Knowledge of regional anatomy and of the characteristic sonographic appearance of the shoulder arthroplasty increases the confidence of the diagnosis.
Acknowledgments
We thank Edward Craig, David Altchek, Answorth Allen, and Charles Cornell
for supplying much of the clinical information.
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