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Clinical Observations |
1 Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710.
Received June 19, 2004;
accepted after revision November 11, 2004.
Presented at the 2004 annual meeting of the American Roentgen Ray Society,
Miami, FL.
Abstract
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CONCLUSION. As opposed to our six patients with clinically and surgically diagnosed internal impingement, the control patients had isolated pathology in the rotator cuff, labrum, or humeral head. We found that the constellation of findings of undersurface tears of the supraspinatus or infraspinatus tendon and cystic changes in the posterior aspect of the humeral head associated with posterosuperior labral pathology is a consistent finding diagnostic of internal impingement.
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The purpose of this study was to evaluate the ability of MRI to show the findings of internal impingement of the shoulder. By noting the findings of internal impingement on MRI and alerting the surgeon to these findings, the radiologist increases the likelihood of a successful surgical outcome for the patient because of the surgeon's awareness of and attention to the underlying disease process.
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Our group of six patients with clinically and surgically diagnosed internal impingement ranged in age from 18 to 36 years (mean age, 23 years). All six patients underwent arthroscopic evaluation and treatment for internal impingement. Three patients were elite college baseball players; one, an amateur baseball player; one, an elite college tennis player; and one, an elite high school swimmer. The 15 control patients were selected with the only criterion of no clinical or surgical diagnosis of internal impingement.
Arthroscopic criteria for the diagnosis of internal impingement included posterosuperior labral fraying or tearing, articular-sided irregularity of the supraspinatus or infraspinatus tendon or of both tendons, and visualized contact of the rotator cuff tendons on the posterosuperior glenoid with the shoulder in abduction and external rotation.
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The following MRI pulse sequences were performed for patients without intraarticular gadolinium: spin-echo T1-weighted sagittal oblique (TR range/TE range, 500-800/15-20); fast spin-echo T2-weighted in three planes (sagittal, coronal, axial) with frequency-selective fat saturation (3,000-5,000/50-65); and proton density in the coronal and axial planes (TR/TE range, 4,000/13-20). MR arthrography sequences were similar except that three-plane (sagittal, coronal, axial) spin-echo T1-weighted imaging was performed with and without frequency-selective fat saturation, and no proton density sequences were performed. The matrix was 256 x 192, and the field of view was 14 cm.
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Two of the six patients were retrospectively diagnosed with internal impingement on the basis of the MRI findings. The MRI reports of the other four patients mentioned specific findings of internal impingement, such as undersurface rotator cuff abnormalities, abnormal signal in the labrum, and cystic changes in the posterior humeral head, but the diagnosis of internal impingement was not mentioned in the dictated report.
On the preoperative shoulder MRI examinations, 100% of our patients versus 27% of the control patients showed abnormalities of the undersurface of the supraspinatus or infraspinatus tendon or of both tendons with abnormal signal or tears identified on oblique coronal and sagittal images (Figs. 1, 2, 3). One hundred percent of our patients versus 27% of the control patients showed cystic changes in the posterosuperior humeral head at the attachment site of the infraspinatus tendon and posterior fibers of the supraspinatus tendon (Fig. 4). One hundred percent of our patients versus 13% of the control patients showed abnormalities of the posterosuperior labrum such as abnormal signal or morphology (or both) (Fig. 5).
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One hundred percent (6 of 6) of our patients, all with clinically and surgically proven internal impingement, versus 27% (4 of 15) of the control patients showed irregularity of the undersurface of the rotator cuff such as abnormal signal, tears, or both as a result of this impingement on the preoperative MRI examinations in the oblique coronal and oblique sagittal images. Davidson et al. [6] stated that internal impingement occurs when the arm is in the cocked position of 90° abduction and full external rotation. However, contact between the rotator cuff and the posterosuperior glenoid can be a normal physiologic finding; internal impingement is diagnosed when pathology occurs in the rotator cuff and labrum as a result of excessive contact.
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In our study, four of six patients displayed signs of excessive shoulder capsular laxity with anterior instability and anterior translation of the humeral head. During overhead throwing movements, the rotator cuff and shoulder capsule function to position and stabilize the humeral head within the glenoid [10, 12]. Laxity is a normal physiologic occurrence in shoulders. Baseball players routinely have glenohumeral laxity. Pathology occurs when there is excessive laxity resulting in anterior instability and translation of the humerus. In prior literature, it has been suggested that excessive glenohumeral joint laxity with anterior translation of the humerus can result in internal impingement with trauma to the rotator cuff, glenoid labrum, and humeral head.
Shoulder laxity formerly was treated by tightening the shoulder capsule with thermal capsulorrhaphy, but current treatment usually consists of capsular plication [13, 14]. Treatment of the abnormal rotator cuff and labrum without correcting the excessive shoulder laxity has resulted in marginal surgical results and, therefore, has caused delays in athletes returning to competition. Payne et al. [15] found the rate of return to competition for the throwing athlete (e.g., baseball player) with excessive shoulder laxity and associated anterior humeral translation to be only 40%. Jobe and Pink [16] also found poor results in this patient population when the excessive shoulder laxity was not corrected at surgery.
One hundred percent of our patients versus 13% of the control patients showed abnormal signal or morphology such as fraying or tears (or both) of the posterosuperior labrum. Walch et al. [5] reported an incidence of 71% of posterosuperior labral lesions in their throwing athletes, and Paley et al. [17] reported an 88% incidence. Throwers can acquire posteroinferior capsular tightness that shifts the humeral head posterosuperiorly within the glenoid during abduction and external rotation [18]. These increased shear forces at the posterosuperior labrum may lead to an increased incidence of posterosuperior degenerative changes in these athletes [19].
Cystlike changes in the humeral head are a consistent occurrence in patients with shoulder internal impingement. One hundred percent of our patients versus 27% of the control patients showed cystic changes within the posterolateral humeral head at the attachment site of the infraspinatus tendon and the posterior fibers of the supraspinatus tendon. These cystlike changes are located in a more posterior position in the humeral head than is typically seen with rotator cuff pathology. We postulate that there is a vascular cause for these humeral cysts. Excessive contact of the humeral head with the glenoid may result in an inflammatory process with increased vascularity eventually leading to these cystlike changes. We suggest that improved shoulder mechanics after successful corrective surgery results in decreased inflammation and resolution of the hypervascularity followed by healing of the bone cystlike changes, which may in fact represent vascular channels. Postoperative MR images of our patients showed disappearance of the cystlike humeral head lesions compared with the preoperative MRI examinations supporting this theory (Figs. 6A and 6B).
Humeral head cystlike lesions are noted often in shoulder imaging. Those due to internal impingement are located posterior in the humerus. The cause of these cysts in the rotator cuff is not clear, and they may result from impaction or traction. However, given that the lesions in internal impingement resolve after surgery, we theorize that it is a reversible cause, such as a vascular or inflammatory cause. The constellation of findings of posterior cystlike changes along with the changes in the cuff and posterosuperior labrum should suggest internal impingement.
In prior literature, arthroscopic rotator cuff débridement was recommended to treat partial thickness undersurface rotator cuff tears and superior labral lesions [6, 18, 20]. This surgery would be incomplete for a patient with internal impingement. Internal impingement is an important entity to diagnose because of the surgical implications, which influence the outcome for the patient. Two of our six patients were prospectively diagnosed with internal impingement on the basis of the MRI findings and clinical history. MR arthrography, although not necessary for the diagnosis of internal impingement, makes the undersurface tears of the infraspinatus tendon more conspicuous. The identification of this undersurface tear could alert the radiologist to additional findings to suggest the diagnosis more confidently. It is important to alert the surgeon of the MRI findings of internal impingement so that the pertinent and appropriate pathology is addressed at surgery. An unsuccessful outcome can result in shortening of an athlete's career and a decreased quality of life for the nonathlete.
Budoff et al. [19] concluded that the kissing lesions of undersurface rotator cuff tears and posterosuperior labral damage could possibly be explained by mechanisms other than internal impingement because they noted this same constellation of lesions in their general patient population. We did not observe these findings in our control population. Those researchers reasoned that recreational athletic patients do not routinely assume the position of extreme abduction and external rotation and thus are unlikely to experience significant internal impingement forces. Our patients were elite athletes and presented with symptoms likely because they experienced significant internal impingement forces. Tirman et al. [1] mentioned that impingement of the rotator cuff on the posterosuperior glenoid labrum is a cause of posterior shoulder pain in throwing athletes. However, they concluded that other than bone marrow abnormalities, findings at MRI were not reliable for the detection of posterosuperior glenoid impingement.
In conclusion, although our study has a small number of patients, a limitation of the study, we found the constellation of findings of partial undersurface tears in the posterior aspect of the rotator cuff along with posterosuperior labral abnormality and posterior cystlike changes in the humeral head is diagnostic of internal impingement.
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