MRI Web Clinic — July 2006

Internal Impingement
Mark H. Awh, M.D.

Clinical History: A 22 year-old professional baseball pitcher presents with persistent posterior shoulder pain after throwing. A fat suppressed T2-weighted oblique coronal image (1a) and a gradient echo T2*-weighted axial image (1b) are provided. What are the findings” What is your diagnosis?

1a
1b
Figure 1:

A fat suppressed T2-weighted oblique coronal image (1a) and a gradient echo T2*-weighted axial image (1b)

Findings

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Figure 2:

(2a) The fat-suppressed T2-weighted coronal image, a small partial articular surface tear (arrow) is evident at the posterior aspect of the supraspinatus insertion. Underlying subchondral cystic changes and reactive marrow edema (arrowhead) are seen within the greater tuberosity.

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Figure 3:

(3a) The gradient echo axial image reveals a complex tear of the posterior superior glenoid labrum (arrow).

Diagnosis

Internal impingement.

Discussion

The extreme stress placed upon the shoulder by the throwing athlete can result in numerous causes of shoulder pain, including rotator cuff tears, labral tears, subacromial impingement, and glenohumeral instability. Internal impingement, also known as posterior superior glenoid impingement, is one of the most common etiologies of posterior shoulder pain in the throwing athlete. Although overhead athletes such as baseball pitchers, tennis players, and javelin throwers are the most at risk, internal impingement may also be seen in the general population due to occupational overhead lifting activities.

Walch et al first described internal impingement in 1992, in a study of 17 overhead athletes.1 Walch found that in abduction and external rotation, contact occurs between the undersurface of the rotator cuff and the glenoid, and that though the contact is physiologic, it may lead to disease when performed forcefully and repetitively, as in the throwing athlete (4a,5a). Jobe agreed with this concept and further expanded upon the entity2,3 by proposing that instability caused by anterior capsular stretching in throwers allowed increased angulation/external rotation, thus increasing contact at the posterior superior glenoid. Although somewhat controversial, recent work has supported the role of laxity in the pathogenesis of internal impingement.4

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Figure 4:

(4a) Viewed from above, a pitcher in the late cocking phase of throwing places the shoulder into extreme abduction and external rotation.

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Figure 5:

(5a) The area of interest from 4a is viewed in this illustration from a superoanterior angle. The close-up view on the right demonstrates how the posterior supraspinatus may infold between the greater tuberosity and the posterior superior labrum. With forceful repetition, articular surface rotator cuff tears (arrow) and labral tears (arrowhead) result. Illustrations courtesy of Michael E. Stadnick, MD.

Pitchers with internal impingement typically complain of pain in the late cocking or early acceleration phase of throwing. The pain is usually described as posterior, and occurs during and after throwing. With disease progression, loss of velocity and accuracy may ensue. On physical exam, posterior pain is recreated in abduction and external rotation. Loss of internal rotation and a positive relocation test (for instability) are common findings. Joint laxity is variably present.

MRI is well recognized as an effective means to diagnose internal impingement of the shoulder.5,6,7 The classic MRI findings of internal impingement, as seen in this month’s case, include partial articular surface tears at the posterior supraspinatus/anterior infraspinatus insertion, greater tuberosity bony changes, and tearing of the posterior superior glenoid labrum. This triad of structures has been documented via arthroscopy, MRI, and cadaveric studies to contact each other in the position of abduction and external rotation. Although the classic MRI appearance of internal impingement involves abnormalities of all three regions, variations often occur in which lesions may predominate in two of the affected areas (6a, 6b).

6a
6b
Figure 6:

(6a) T1- and (6b) fat-suppressed T2-weighted images in a professional baseball player with clinical signs of internal impingement reveal prominent cystic changes within the posterior greater tuberosity (arrows). Subtle articular surface partial tearing is seen at the posterior supraspinatus insertion on the T2-weighted view (arrowhead). No labral tear was found in this patient.

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Figure 7:

(7a) A T2-weighted coronal image in a professional baseball pitcher with clinically presumed internal impingement does not demonstrate a rotator cuff tear. However, an osseous lesion is present within the posterior greater tuberosity (arrow) and striking degeneration and edema (arrowheads) are apparent within the posterior aspect of the superior labrum.

The use of paramagnetic contrast has proven beneficial in the evaluation of internal impingement. Direct MR arthrography improves the visualization of both labral tears and partial articular surface cuff tears as compared to routine MRI.5 We have been successful in visualizing internal impingement utilizing MRI following intravenous administration of gadolinium chelates. Immediate post-contrast imaging in patients with internal impingement reveals enhancement within articular surface rotator cuff tears, labral tears, and within humeral head osseous abnormalities (8a,8b,9a).

8a
8b
Figure 8:

Focal enhancement is seen within a small partial articular surface supraspinatus tear (arrow) and within the adjacent greater tuberosity (arrowhead) on these (8a,8b) fat-suppressed T1-weighted coronal images obtained following intravenous contrast administration in a 25 year-old professional baseball pitcher.

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Figure 9:

(9a) The corresponding fat-suppressed T1-weighted axial view demonstrates an irregular, enhancing posterior superior glenoid labrum (arrow).

The osteochondral lesions seen within the humeral head in internal impingement are of uncertain etiology. Some authors have suggested that the cystic changes within the humeral head in the throwing athlete are due to repetitive avulsive trauma caused by deceleration during the follow-through motion of throwing.8 The anatomical relationships demonstrated in studies of internal impingement suggest impaction as perhaps a more likely etiology. Recently, it has been suggested that the repetitive contact of the greater tuberosity with the glenoid in abduction external rotation results in an inflammatory process, with increased vascularity accounting for the osseous changes.7 In some patients, post-operative MRI has revealed disappearance of the cystic lesions, lending support to an inflammatory etiology.

Jobe has categorized the clinical presentation of internal impingement into three stages.9 In Stage I, athletes present with shoulder stiffness that requires an extended warm-up period. In Stage II, patients complain of posterior shoulder pain and have a positive relocation test. This test, performed on the supine patient, causes apprehension when pressure is placed upon the back of the humeral head in abduction and external rotation. With a positive relocation test, pain and apprehension are relieved by application of pressure over the anterior humeral head. The relief of pain is presumably related to both a reduction of humeral head subluxation and due to disengagement of the rotator cuff from the region of internal impingement. Successful rehabilitation in Stage II patients results in pain resolution and a negative relocation test. With Stage III internal impingement, pain and a positive relocation test persist after rehabilitation. Jobe feels that such patients require surgical repair of their rotator cuff and/or labral pathology as well as a modified anterior capsulolabral shift.

Conclusion

Internal impingement is one of many potential causes of shoulder pain in the overhead throwing athlete. The recognition on MRI of the classic findings of articular surface partial rotator cuff tears, greater tuberosity osseous lesions, and posterior superior labral tears allows one to make an accurate diagnosis in such patients. As many orthopaedic surgeons feel that instability is an important factor in the pathogenesis of internal impingement, the correct diagnosis is critical so that instability can be addressed as needed at the time of rotator cuff or labral repair, thereby increasing the chances for a successful operative outcome.

References

1 Walch G, Boileau P, Noel E, Donell ST. Impingement of the deep surface of the supraspinatus tendon on the posterosuperior glenoid rim: an arthroscopic study. J Shoulder Elbow Surg1992; 1:238 “245.

2 Jobe CM. Evidence for a superior glenoid impingement upon the rotator cuff. J Shoulder Elbow Surg 1993; 2(part 2):S19.

3 Jove CM. Posterior superior glenoid impingement: expanded spectrum. Arthroscopy 1995;11:530-536.

4 Burkehart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology. I. Pathoanatomy and biomechanics. Arthroscopy 2003;19 : 404-420.

5 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: 431-436.

6 Halbrecht JL, Tirman P, Atkin D. Internal impingement of the shoulder: comparison of findings between the throwing and nonthrowing shoulders of college baseball players. Arthroscopy 1999;15 : 253-258.

7 Giaroli EL, Major NM, Higgins LD. MRI of internal impingement of the shoulder. AJR 2005; 185:925-929.

8 Burk DL, Torres JL, Marone PJ, et al. MR imaging of shoulder injuries in professional baseball players. JMRI 1991: 1:385-389.

9 Jobe CM. Superior glenoid impingement: current concept. Clin Orthop 1996;330: 98-107.

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