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1 Department of Diagnostic Imaging, McMaster University and Hamilton Health
Sciences, 1003-81 Charlton Ave. E, Hamilton, ON, Canada, L8N 1Y7.
2 Department of Diagnostic Imaging, McMaster University and Hamilton Health
Sciences, Henderson General Hospital, 711 Concession St., Hamilton, ON, Canada
L8V 1C3.
3 Department of Diagnostic Imaging, St. Joseph's Hospital, 50 Charlton Ave. E,
Hamilton, ON, Canada L8N 4A6.
4 Department of Orthopaedic Surgery, Guelph General Hospital, 115 Delhi St.,
Guelph, ON, Canada N1E 4J4.
5 Department of Orthopaedic Surgery, St. Mary's Hospital, 911 Queen's Blvd.,
Kitchener, ON, Canada N2M 1B2.
Received October 23, 2003;
accepted after revision June 14, 2004.
Address correspondence to M. Ferri.
Abstract
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SUBJECTS AND METHODS. Twenty-one patients with full-thickness supraspinatus tears underwent shoulder sonography in both the Crass and the modified Crass positions. Measurements of supraspinatus tears were performed in the sagittal and transverse dimensions. Patients subsequently underwent either arthroscopic or open supraspinatus repair. Intraoperative measurements were made in two dimensions and were compared with sonographic findings.
RESULTS. Sonography had 100% specificity in detecting full-thickness supraspinatus tears. No statistically significant difference was seen between the size of supraspinatus tears in the Crass and modified Crass positions and surgical findings in the transverse plane (p = 0.55 and 0.61, respectively). In the sagittal dimension, no statistically significant difference was seen between surgical findings and the Crass position (p = 0.14); however, a difference existed when the modified Crass position was used (p = 0.03).
CONCLUSION. Sonography reliably detects and quantifies supraspinatus tears. Both the Crass and the modified Crass positions reflected the true size of supraspinatus tears in the transverse plane. In the sagittal plane, the Crass position is the more useful to quantify supraspinatus tears because the modified Crass position overestimates the size of such tears.
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The purpose of our study was to determine prospectively whether the Crass or the modified Crass position [7] affords the most accurate measure of supraspinatus tendon tears when compared with arthroscopic or open surgical findings, using intraoperative measurements as the gold standard. To date, a limited number of trials have examined the correlation of sonography with surgical findings, none of which correlated measurement of rotator cuff tears in the Crass and modified Crass positions with surgical measures. Because technique is a major factor in the accuracy of rotator cuff sonography, determining the shoulder position that most the accurately reflects the true size of supraspinatus tears is useful.
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Patients
The study population was selected prospectively from patients with
suspected rotator cuff disorders who were referred for shoulder sonographic
assessment. Twenty-one consecutive patients with full-thickness tears of the
supraspinatus tendon diagnosed on sonography were included in our analysis.
None of these patients had prior rotator cuff surgery. The study population
included seven women and 14 men (age range, 41-83 years). Each patient had
unilateral disease; nine had left-sided disease, and 12 had right. Each
patient underwent complete bilateral sonographic examination using a 700 MR
machine (GE Healthcare) and a 7.5-13-MHz multifrequency linear array probe.
Supraspinatus tears were measured in both the Crass and the modified Crass
positions in the sagittal and transverse planes with respect to the
supraspinatus fibers. The sonographic examinations were performed by one
experienced sonographer and were interpreted by one experienced
musculoskeletal radiologist.
After the sonographic examination, each patient underwent rotator cuff repair, either arthroscopically or by open technique, by one of two orthopedic surgeons. Associated procedures, such as acromioplasty and excision of the distal clavicle, were performed as deemed necessary at the time of surgery. The average delay between sonographic assessment and surgery was 3 months (range, 1 month-1 year). Thirteen patients underwent repair within 3 months from the time of sonography, six tears were repaired between 3 and 5 months from the time of the sonography, and only one patient each had a delay of 7 months and 1 year. Eleven patients underwent arthroscopic repair, eight of which repairs were converted to open repairs at the time of surgery. Two patients proceeded directly to open repair.
Either a sterile ruler (open repair) or the tip of an arthroscopic instrument of known length (arthroscopic repair) was used to measure the supraspinatus tears intraoperatively, both in the sagittal and the transverse planes, relative to the orientation of the tendon fibers (Figs. 1A, 1B, 2A, and 2B). The measurements of the supraspinatus tears in the Crass and the modified Crass positions in both planes (Figs. 3A, 3B, 4A, and 4B) were compared with each other and then with the operative findings using paired t tests.
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Technique
All examinations are best performed using a multifrequency 7.5-13-MHz
linear array transducer. It is vital that both the depth and the near field be
continually changed. For example, the anterior shoulder is best assessed using
a near focus and high frequency
[7,
12,
13].
Positioning is a key component of the sonographic examination. In the neutral position, most rotator cuff is obscured by the overlying acromion. Crass et al. [7], in 1987, advocated that the shoulder be positioned in extension, adduction, and internal rotation to improve visualization of the supraspinatus tendon, thus augmenting diagnostic accuracy (Figs. 5A, 5B, 5C, 6A, 6B, and 6C). This position has since been referred to as the Crass position. The patient is seated and the shoulder is extended, adducted, and internally rotated with the elbow flexed, the palm facing out, and the fingers pointing toward the contralateral scapula (Figs. 7A and 7B). Internal rotation allows the supraspinatus to become an anterior structure, and extension draws the supraspinatus anteriorly from beneath the acromion, allowing the maximal length of tendon to be visualized. Dynamic scanning is not possible in this position. Crass et al. [7] believed that the need for dynamic scanning is eliminated by the additional information provided by this position. It was also reported that a small percentage of patients overly internally rotate the shoulder, obscuring the most anterior portion of the supraspinatus tendon [7].
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The anterior portion of the supraspinatus tendon is defined by the position of the bicipital groove. If the bicipital groove is not seen in the routine position, Crass et al. [7] advocated the use of the modified Crass position, wherein the patient places the hand on the hip with the elbow pulled back. In the modified Crass position, which is helpful in examination of the anteromedial aspect of the tendon, the shoulder is extended, the elbow is flexed, and the palm of hand is against the back pocket [2] (Figs. 7A and 7B). In 1992, Middleton [4] preferred the modified Crass position because it avoids internal rotation and maintains the view of the intraarticular portion of the biceps tendon and the most anterior portion of the supraspinatus (Figs. 5A, 5B, 5C, 6A, 6B, and 6C). The appearance of the supraspinatus tendon changes from the Crass to the modified Crass position in that it rotates 90° from an anterior to a lateral position (Figs. 5A, 5B, 5C, 6A, 6B, 6C, 7A, and 7B). Localizing the biceps tendon facilitates appropriate identification of the supraspinatus and subscapularis tendons [4].
Both sagittal and transverse views of the supraspinatus are crucial to detection of supraspinatus tears. "Sagittal" and "transverse" refer to the orientation of the sonographic transducer to the long axis of the supraspinatus fibers. The rotator cuff and scapula are oriented at approximately 45° to the body's sagittal and coronal planes, and sagittal supraspinatus views are obtained in a plane approximately half way between sagittal and coronal [4]. Because of the long and broad nature of the supraspinatus tendon, it is crucial to identify its entire course to avoid false-negative results.
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In the modified Crass position, the mean transverse length was 1.7 cm, which was not statistically significant when compared with the operative mean of 1.8 cm (p = 0.61). However, a significant difference was seen between the modified Crass sagittal measurement (1.9 cm) and the corresponding operative finding of 1.5 cm (p = 0.03).
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In a large trial by Wiener and Seitz [3] in 1992, preoperative sonography in the modified Crass position was performed on 225 patients and findings were correlated with arthroscopic inspection or open surgery. Partial-thickness tears were diagnosed when any of the following criteria were met: a focal hypoechoic zone, multiple small hypoechoic discontinuities, or large dominant linear echogenic foci within the substance of the cuff. Full-thickness tears were defined as the presence of a hypoechoic zone extending through the entire substance of the cuff or loss of substance with visualized tear margins. Massive tears were those in which the rotator cuff was not visualized and the deltoid muscle approximated the humeral head. In 206 (92%) of 225 patients, the sonographic findings were confirmed. Sonography underestimated the extent of cuff injury in 11 patients (5%) and overestimated it in eight patients (4%) [3].
Farin et al. [15], in 1996, examined the use of sonography, double-contrast arthrography, and contrast-enhanced CT arthrography in assessing the site and size of rotator cuff tears. Patient positioning was not described. Sonography detected 80% of partial- and 90% of full-thickness tears with one false-positive finding. The size of the tear was accurately identified on sonography in 70% of cases; tears were overestimated in 2% and underestimated in 9% of cases [15].
We reviewed the literature regarding the sensitivity and specificity of sonography of the rotator cuff compared with surgical findings. Most authors advocated the use of sonography to both detect and quantify supraspinatus tears. Unfortunately, most authors did not provide reproducible descriptions of patient positioning during sonographic examination, and therefore conclusions regarding the accuracy of tear measurement as related to shoulder positioning cannot be made on the basis of the current literature.
Previous trials have examined the use of sonography in detecting and accurately measuring the size of supraspinatus tears. However, either the position of the shoulder joint was not specified, or sonography was performed with the shoulder held in one position: the neutral, the Crass, or the modified Crass position. Because patient positioning is crucial to appropriate sonographic investigation of the shoulder, we believed it relevant to assess the ability of the Crass and modified Crass positions to quantify accurately the size of supraspinatus tears as compared with operative findings. Because the size of the supraspinatus tear can affect the operative approach, it is important to quantify accurately the size of full-thickness supraspinatus tears.
A limitation of this trial was our small sample size of 21 patients. Furthermore, an arthroscopic instrument of known length was used to measure the tears in the small arthroscopic operative field; it is unknown whether measurement accuracy was compromised. During the open supraspinatus repair, intraoperative measurements were made along the contour of the greater tuberosity because the malleable ruler can assume the shape of the tuberosity. During sonography, measurement of supraspinatus tears was made using straight lines between calipers, which may have affected our data adversely. Finally, the sonographer and radiologists involved in our trial are experienced in musculoskeletal radiology, which likely contributed to the accuracy of the sonographic and operative findings. Therefore, our findings may not be reproducible among radiologists who are not experienced in musculoskeletal sonography.
On the basis of our findings, both the Crass and the modified Crass positions reflect the true size of full-thickness supraspinatus tears in the transverse plane when compared with operative findings. Conversely, sagittal measures in the modified Crass position significantly overestimate the size of full-thickness supraspinatus tears, yet the Crass position reflects the true size of tears in the sagittal plane. It is conceivable that the two positions could create a difference in tension across full-thickness supraspinatus tears, thus affecting the resultant measurement in the sagittal plane. External rotation, a component of the modified Crass position, may increase tension along the length of the tendon fibers, resulting in overestimation of tear size in the longitudinal plane. In contradistinction to the modified Crass position, the Crass position more closely mimics the adducted position of the shoulder at the time of surgery, thus potentially contributing to the improved accuracy of tear measurement in this position.
In conclusion, we recommend that the radiologist performing and interpreting shoulder sonography recognize that the sagittal measurement of full-thickness supraspinatus tears is more accurately performed with the shoulder in the Crass position.
Acknowledgments
We thank Bruce Weaver of McMaster University.
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