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AJR 2005;185:925–929

0361–803X/05/1854–925

© American Roentgen Ray Society

Giaroli et al.MRI of Internal Impingement of the Shoulder

M u s c u l o s ke l e t a l I m ag i n g • C l i n i c a l O b s e r v a t i o n s

MRI of Internal Impingement of the Shoulder

Eddie L. Giaroli1Nancy M. MajorLaurence D. Higgins

Giaroli EL, Major NM, Higgins LD

DOI:10.2214/AJR.04.0971

Presented at the 2004 annual meeting of the American Roentgen Ray Society, Miami, FL.

Received June 19, 2004; accepted after revision November 11, 2004.

1All authors: Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710. Address correspondence to N. M. Major.

OBJECTIVE. Internal impingement is a condition that occurs in athletes in which theshoulder is put in extreme abduction and external rotation during overhead movements. Duringthis motion, the posterior fibers of the supraspinatus tendon, anterior fibers of the infraspinatustendon, or both can get impinged between the humeral head and the posterior glenoid. The pur-pose of this study was to evaluate the ability of MRI to show the findings of internal impinge-ment of the shoulder.

CONCLUSION. As opposed to our six patients with clinically and surgically diagnosedinternal 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 su-praspinatus or infraspinatus tendon and cystic changes in the posterior aspect of the humeralhead associated with posterosuperior labral pathology is a consistent finding diagnostic of in-ternal impingement.

nternal impingement, also knownas posterosuperior impingementin prior orthopedics and radiologyliterature [1], is a condition that

occurs in athletes in which the shoulder is putin extreme abduction and external rotationduring overhead movements. During this mo-tion, either the supraspinatus or infraspinatustendon or both tendons can become entrappedbetween the humeral head and the posteriorglenoid. Pathology findings can be seen to in-volve the supraspinatus and infraspinatus ten-dons, posterosuperior labrum, and humeralhead. It is important to note that it can be anormal physiologic finding for the undersur-face of the rotator cuff (i.e., supraspinatus andinfraspinatus tendons) to contact the postero-superior glenoid with overhead movement[2–4]. A diagnosis of internal impingementimplies that there are pathology findings as aresult of this contact [5–10].

The purpose of this study was to evaluatethe ability of MRI to show the findings ofinternal impingement of the shoulder. Bynoting the findings of internal impingementon MRI and alerting the surgeon to thesefindings, the radiologist increases the likeli-hood of a successful surgical outcome forthe patient because of the surgeon’s aware-ness of and attention to the underlying dis-ease process.

Materials and MethodsThe preoperative shoulder MRI examinations of

six patients with clinically diagnosed and subse-quently surgically confirmed internal impingementwere reviewed retrospectively. The findings werethen prospectively compared with the shoulderMRI examinations of 15 control patients without aclinical or surgical diagnosis of internal impinge-ment. More specifically, the control group con-sisted of nonathletes or patients who did not give ahistory of participating routinely in a throwingsport. Abnormal findings associated with the su-praspinatus and infraspinatus tendons, labrum, andhumeral head were noted. All MRI examinationswere retrospectively reviewed by four board-certi-fied radiologists.

Our group of six patients with clinically and sur-gically diagnosed internal impingement ranged inage from 18 to 36 years (mean age, 23 years). All sixpatients underwent arthroscopic evaluation and treat-ment for internal impingement. Three patients wereelite college baseball players; one, an amateur base-ball player; one, an elite college tennis player; andone, an elite high school swimmer. The 15 control pa-tients were selected with the only criterion of no clin-ical or surgical diagnosis of internal impingement.

Arthroscopic criteria for the diagnosis of inter-nal impingement included posterosuperior labralfraying or tearing, articular-sided irregularity of thesupraspinatus or infraspinatus tendon or of bothtendons, and visualized contact of the rotator cuff

I

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Fig. 1—20-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. 2—20-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. 3—17-year-old girl in abduction external rotation. Fat-suppressed proton density image shows infraspinatus being impinged by posterosuperior glenoid labrum (arrow).

Fig. 4—20-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).

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tendons on the posterosuperior glenoid with theshoulder in abduction and external rotation.

All patients were imaged in the supine positionwith arms extended in a neutral position on a 1.5-Tmagnet with a shoulder coil. All six patients withinternal impingement were imaged after intraartic-ular administration of gadolinium contrast mate-rial. Six of the 15 control patients were imaged afterintraarticular gadolinium administration, and theremaining nine were imaged with routine MRIwithout intraarticular gadolinium.

The following MRI pulse sequences were per-formed for patients without intraarticular gadolin-ium: spin-echo T1-weighted sagittal oblique (TRrange/TE range, 500–800/15–20); fast spin-echoT2-weighted in three planes (sagittal, coronal, ax-ial) with frequency-selective fat saturation(3,000–5,000/50–65); and proton density in thecoronal and axial planes (TR/TE range,4,000/13–20). MR arthrography sequences weresimilar except that three-plane (sagittal, coronal,axial) spin-echo T1-weighted imaging was per-formed with and without frequency-selective fatsaturation, and no proton density sequences wereperformed. The matrix was 256 × 192, and the fieldof view was 14 cm.

ResultsAll six of our patients showed direct signs

of internal impingement on the arthroscopicexamination, which was performed with the

patient under anesthesia and the arm in the ab-duction and external rotation position. Theundersurface of the supraspinatus or in-fraspinatus tendon or of both tendons con-tacted the posterosuperior labrum and therewere pathologic findings as a result of thiscontact, including fraying and undersurfacetears. Four of the six patients showed anteriorinstability during this physical examinationwith anterior translation of the humeral head.All four of these patients also showed poste-rior instability, with three of the four display-ing inferior instability.

Two of the six patients were retrospec-tively diagnosed with internal impingementon the basis of the MRI findings. The MRI re-ports of the other four patients mentioned spe-cific findings of internal impingement, suchas undersurface rotator cuff abnormalities,abnormal signal in the labrum, and cysticchanges in the posterior humeral head, but thediagnosis of internal impingement was notmentioned in the dictated report.

On the preoperative shoulder MRI examina-tions, 100% of our patients versus 27% of thecontrol patients showed abnormalities of theundersurface of the supraspinatus or infraspina-tus tendon or of both tendons with abnormalsignal or tears identified on oblique coronal andsagittal images (Figs. 1–3). One hundred per-cent of our patients versus 27% of the control

patients showed cystic changes in the postero-superior humeral head at the attachment site ofthe infraspinatus tendon and posterior fibers ofthe supraspinatus tendon (Fig. 4). One hundredpercent of our patients versus 13% of the con-trol patients showed abnormalities of the pos-terosuperior labrum such as abnormal signal ormorphology (or both) (Fig. 5).

DiscussionInternal impingement was discussed by

Walch et al. [5] in 1992 and applied to thethrowing shoulder by Jobe [7] and others [6]shortly thereafter. With extreme external rota-tion in abduction, contact is made between thegreater tuberosity and posterosuperior glenoidrim. With repetitive contact, injury occurs tothe abutting structures of the rotator cuff andposterosuperior labrum. Internal impingementoccurs in the late cocking phase of the throw-ing motion. The clinical entity is exacerbatedby anterior laxity, loss of normal posteriortranslation in the glenohumeral joint, and de-creased humeral retroversion [11].

One hundred percent (6 of 6) of our patients,all with clinically and surgically proven inter-nal impingement, versus 27% (4 of 15) of thecontrol patients showed irregularity of the un-dersurface of the rotator cuff such as abnormalsignal, tears, or both as a result of this impinge-ment on the preoperative MRI examinations in

Fig. 5—20-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.

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the oblique coronal and oblique sagittal im-ages. Davidson et al. [6] stated that internal im-pingement occurs when the arm is in thecocked position of 90° abduction and full ex-ternal rotation. However, contact between therotator cuff and the posterosuperior glenoidcan be a normal physiologic finding; internalimpingement is diagnosed when pathology oc-curs in the rotator cuff and labrum as a result ofexcessive contact.

Clinically, patients present with posterosu-perior shoulder pain that is sometimes associ-ated with anterior instability. This entity oc-curs most commonly in athletes whoconsistently place their shoulder in the abduc-tion and external rotation position, such asbaseball players, tennis players, swimmers,and javelin throwers. The pain and instabilityare most pronounced with the arm in the max-imum abduction and external rotation posi-tion at the beginning of the acceleration phaseof forward arm movement.

In our study, four of six patients displayedsigns of excessive shoulder capsular laxitywith anterior instability and anterior transla-tion of the humeral head. During overheadthrowing movements, the rotator cuff and

shoulder capsule function to position and sta-bilize the humeral head within the glenoid[10, 12]. Laxity is a normal physiologic oc-currence in shoulders. Baseball players rou-tinely have glenohumeral laxity. Pathologyoccurs when there is excessive laxity result-ing in anterior instability and translation ofthe humerus. In prior literature, it has beensuggested that excessive glenohumeral jointlaxity with anterior translation of the humeruscan result in internal impingement withtrauma to the rotator cuff, glenoid labrum,and humeral head.

Shoulder laxity formerly was treated bytightening the shoulder capsule with thermalcapsulorrhaphy, but current treatment usuallyconsists of capsular plication [13, 14]. Treat-ment of the abnormal rotator cuff and labrumwithout correcting the excessive shoulderlaxity has resulted in marginal surgical resultsand, therefore, has caused delays in athletesreturning to competition. Payne et al. [15]found the rate of return to competition for thethrowing athlete (e.g., baseball player) withexcessive shoulder laxity and associated ante-rior humeral translation to be only 40%. Jobeand Pink [16] also found poor results in this

patient population when the excessive shoul-der laxity was not corrected at surgery.

One hundred percent of our patients versus13% of the control patients showed abnormalsignal 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 theirthrowing athletes, and Paley et al. [17] re-ported an 88% incidence. Throwers can ac-quire posteroinferior capsular tightness thatshifts the humeral head posterosuperiorlywithin the glenoid during abduction and ex-ternal rotation [18]. These increased shearforces at the posterosuperior labrum may leadto an increased incidence of posterosuperiordegenerative changes in these athletes [19].

Cystlike changes in the humeral head are aconsistent occurrence in patients with shoul-der internal impingement. One hundred per-cent of our patients versus 27% of the controlpatients showed cystic changes within theposterolateral humeral head at the attachmentsite of the infraspinatus tendon and the poste-rior fibers of the supraspinatus tendon. Thesecystlike changes are located in a more poste-rior position in the humeral head than is typi-

A B

Fig. 6—20-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).

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cally seen with rotator cuff pathology. Wepostulate that there is a vascular cause forthese humeral cysts. Excessive contact of thehumeral head with the glenoid may result inan inflammatory process with increased vas-cularity eventually leading to these cystlikechanges. We suggest that improved shouldermechanics after successful corrective surgeryresults in decreased inflammation and resolu-tion of the hypervascularity followed by heal-ing of the bone cystlike changes, which mayin fact represent vascular channels. Postoper-ative MR images of our patients showed dis-appearance of the cystlike humeral head le-sions compared with the preoperative MRIexaminations supporting this theory (Fig. 6).

Humeral head cystlike lesions are noted of-ten in shoulder imaging. Those due to internalimpingement are located posterior in the hu-merus. The cause of these cysts in the rotatorcuff is not clear, and they may result from im-paction or traction. However, given that thelesions in internal impingement resolve aftersurgery, we theorize that it is a reversiblecause, such as a vascular or inflammatorycause. The constellation of findings of poste-rior cystlike changes along with the changesin the cuff and posterosuperior labrum shouldsuggest internal impingement.

In prior literature, arthroscopic rotatorcuff débridement was recommended to treatpartial thickness undersurface rotator cufftears and superior labral lesions [6, 18, 20].This surgery would be incomplete for a pa-tient with internal impingement. Internalimpingement is an important entity to diag-nose because of the surgical implications,which influence the outcome for the patient.Two of our six patients were prospectivelydiagnosed with internal impingement on thebasis of the MRI findings and clinical his-tory. MR arthrography, although not neces-sary for the diagnosis of internal impinge-ment, makes the undersurface tears of theinfraspinatus tendon more conspicuous. Theidentification of this undersurface tearcould alert the radiologist to additional find-ings to suggest the diagnosis more confi-dently. It is important to alert the surgeon ofthe MRI findings of internal impingementso that the pertinent and appropriate pathol-ogy is addressed at surgery. An unsuccess-

ful outcome can result in shortening of anathlete’s career and a decreased quality oflife for the nonathlete.

Budoff et al. [19] concluded that the kiss-ing lesions of undersurface rotator cuff tearsand posterosuperior labral damage couldpossibly be explained by mechanisms otherthan internal impingement because theynoted this same constellation of lesions intheir general patient population. We did notobserve these findings in our control popula-tion. Those researchers reasoned that recre-ational athletic patients do not routinely as-sume the position of extreme abduction andexternal rotation and thus are unlikely to ex-perience significant internal impingementforces. Our patients were elite athletes andpresented with symptoms likely becausethey experienced significant internal im-pingement forces. Tirman et al. [1] men-tioned that impingement of the rotator cuffon the posterosuperior glenoid labrum is acause of posterior shoulder pain in throwingathletes. However, they concluded that otherthan bone marrow abnormalities, findings atMRI were not reliable for the detection ofposterosuperior glenoid impingement.

In conclusion, although our study has asmall number of patients, a limitation of thestudy, we found the constellation of findingsof partial undersurface tears in the posterioraspect of the rotator cuff along with postero-superior labral abnormality and posteriorcystlike changes in the humeral head is diag-nostic of internal impingement.

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