Musculoskeletal Imaging Clinical Observations

Transcription

1 MRI of Internal Impingement of the Shoulder Musculoskeletal Imaging Clinical Observations Eddie L. Giaroli 1 Nancy M. Major Laurence D. Higgins Giaroli EL, Major NM, Higgins LD DOI: /AJR Presented at the 2004 annual meeting of the American Roentgen Ray Society, Miami, FL. Received June 19, 2004; accepted after revision November 11, All authors: Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC Address correspondence to N. M. Major. AJR 2005;185: X/05/ American Roentgen Ray Society MRI of Internal Impingement of the Shoulder OBJECTIVE. Internal impingement is a condition that occurs in athletes in which the shoulder is put in extreme abduction and external rotation during overhead movements. During this motion, the posterior fibers of the supraspinatus tendon, anterior fibers of the infraspinatus tendon, or both can get impinged between the humeral head and the posterior glenoid. The purpose of this study was to evaluate the ability of MRI to show the findings of internal impingement of the shoulder. 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. nternal impingement, also known I as posterosuperior impingement in prior orthopedics and radiology literature [1], is a condition that occurs in athletes in which the shoulder is put in extreme abduction and external rotation during overhead movements. During this motion, either the supraspinatus or infraspinatus tendon or both tendons can become entrapped between the humeral head and the posterior glenoid. Pathology findings can be seen to involve the supraspinatus and infraspinatus tendons, posterosuperior labrum, and humeral head. It is important to note that it can be a normal physiologic finding for the undersurface of the rotator cuff (i.e., supraspinatus and infraspinatus tendons) to contact the posterosuperior glenoid with overhead movement [2 4]. A diagnosis of internal impingement implies that there are pathology findings as a result of this contact [5 10]. 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. Materials and Methods The preoperative shoulder MRI examinations of six patients with clinically diagnosed and subsequently surgically confirmed internal impingement were reviewed retrospectively. The findings were then prospectively compared with the shoulder MRI examinations of 15 control patients without a clinical or surgical diagnosis of internal impingement. More specifically, the control group consisted of nonathletes or patients who did not give a history of participating routinely in a throwing sport. Abnormal findings associated with the supraspinatus and infraspinatus tendons, labrum, and humeral head were noted. All MRI examinations were retrospectively reviewed by four board-certified radiologists. 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 AJR:185, October

2 Fig year-old man with supraspinatus tendinosis. Oblique coronal fast spin-echo T2-weighted MR image shows supraspinatus tendon has increased signal near its insertion on greater tuberosity (arrow). Cystic changes are incidentally noted in humeral head. Fig year-old man with infraspinatus tendinosis. Oblique coronal fast spin-echo T2-weighted MR image shows infraspinatus tendon has increased signal near it insertion on greater tuberosity (arrow). Cystic changes are incidentally noted in humeral head near attachment of infraspinatus tendon. Fig year-old girl in abduction external rotation. Fat-suppressed proton density image shows infraspinatus being impinged by posterosuperior glenoid labrum (arrow). Fig year-old man with cystic changes in humeral head. Axial fast spin-echo T2-weighted MR image shows cystic changes in posterosuperior humeral head near attachment sites of supraspinatus and infraspinatus tendons (arrow). 926 AJR:185, October 2005

3 MRI of Internal Impingement of the Shoulder Fig year-old man with abnormal posterior glenoid labrum. Axial fast spin-echo T2-weighted MR image shows posterior labrum has abnormal signal and morphology (arrow). Normally, labrum should maintain decreased T2 signal and be shape of triangle. tendons on the posterosuperior glenoid with the shoulder in abduction and external rotation. All patients were imaged in the supine position with arms extended in a neutral position on a 1.5-T magnet with a shoulder coil. All six patients with internal impingement were imaged after intraarticular administration of gadolinium contrast material. Six of the 15 control patients were imaged after intraarticular gadolinium administration, and the remaining nine were imaged with routine MRI without intraarticular gadolinium. The following MRI pulse sequences were performed for patients without intraarticular gadolinium: spin-echo T1-weighted sagittal oblique (TR range/te range, /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 , and the field of view was 14 cm. Results All six of our patients showed direct signs of internal impingement on the arthroscopic examination, which was performed with the patient under anesthesia and the arm in the abduction and external rotation position. The undersurface of the supraspinatus or infraspinatus tendon or of both tendons contacted the posterosuperior labrum and there were pathologic findings as a result of this contact, including fraying and undersurface tears. Four of the six patients showed anterior instability during this physical examination with anterior translation of the humeral head. All four of these patients also showed posterior instability, with three of the four displaying inferior instability. 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 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). Discussion Internal impingement was discussed by Walch et al. [5] in 1992 and applied to the throwing shoulder by Jobe [7] and others [6] shortly thereafter. With extreme external rotation in abduction, contact is made between the greater tuberosity and posterosuperior glenoid rim. With repetitive contact, injury occurs to the abutting structures of the rotator cuff and posterosuperior labrum. Internal impingement occurs in the late cocking phase of the throwing motion. The clinical entity is exacerbated by anterior laxity, loss of normal posterior translation in the glenohumeral joint, and decreased humeral retroversion [11]. 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 AJR:185, October

4 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. Clinically, patients present with posterosuperior shoulder pain that is sometimes associated with anterior instability. This entity occurs most commonly in athletes who consistently place their shoulder in the abduction and external rotation position, such as baseball players, tennis players, swimmers, and javelin throwers. The pain and instability are most pronounced with the arm in the maximum abduction and external rotation position at the beginning of the acceleration phase of forward arm movement. 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 A Fig year-old man. MRI shows significant improvement in humeral head cystic changes after patient underwent corrective surgery for internal impingement. A, Axial fast spin-echo T2-weighted preoperative MR image shows prominent cystic changes in humeral head near attachment sites of supraspinatus and infraspinatus tendons (arrow). B, Axial fast spin-echo T2-weighted postoperative MR image shows nearly complete resolution of humeral head cystic changes (arrow). 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 typi- B 928 AJR:185, October 2005

5 MRI of Internal Impingement of the Shoulder cally 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 (Fig. 6). 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. References 1. Tirman PFJ, Bost FW, Garvin GJ, et al. Posterosuperior glenoid impingement of the shoulder: findings at MR imaging and MR arthrography with arthroscopic correlation. Radiology 1994; 193: Halbrecht JL. Internal impingement of the shoulder: comparison of findings between the throwing and nonthrowing shoulders of college baseball players. Arthroscopy 1999; 15: Barber FA, Morgan CD, Burkhart SS, Jobe CM. Labrum/biceps/cuff dysfunction in the throwing athlete. Arthroscopy 1999; 15: McFarland EG, Hsu CY, O Neil O. Internal impingement of the shoulder: a clinical and arthroscopic analysis. 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