| May 2006 Case of the Month | |
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Compiled By: William Renner, M.D.
History: A 22-year-old male in a four wheeler accident 2 weeks ago.
Exam: MRI of Shoulder. PD Axial and Coronal T2 Fat Saturated Images.
Findings: (Fig. 1) Sequential axial PD images through the labrum demonstrate an osseous defect of the glenoid rim, inferior labral tear (white arrow) as well as disruptions of the joint capsule and the posterior band of the inferior glenohumeral ligament (black arrow). Note the subscapularis tendon interstitial tear with tendinopathy and associated peritendinitis of the long head of the biceps tendon. All of these abnormalities are presumably traumatic.
(Fig. 2) Coronal T2 Fat Sat image shows a full-thickness supraspinatus tendon tear (black arrow) with posttraumatic deformity and a microtrabecular infraction of the humeral head (white arrow). A multiloculated paralabral cyst is also present (small white arrow).
Diagnosis: Posttraumatic posterior shoulder instability with reverse Hill-Sachs deformity and reverse (posterior) Bankart & HAGL lesions.
Discussion: Posterior shoulder instability is an uncommon but debilitating condition of young adults that is being diagnosed with increased frequency. Isolated posterior instability is uncommon accounting for less than 5% of all shoulder instability. Moreover, only 2-4% of acute dislocations are posterior in location. These uncommon acute posterior dislocations may follow trauma, as in this case, but are more common after electrical shock or seizures. Recurrent posterior subluxation is much more common than acute dislocation.
Posterior instability occurs in swimmers, overhead throwing athletes and punching athletes due to overuse with microtrauma. Posterior instability may also be part of multidirectional instability in those with inherent laxity of the shoulder joint.
The lesions associated with posterior instability have the same eponyms associated with anterior instability except “reverse” is added to indicate the opposite location. A “reverse Hill-Sachs” lesion is an anteromedial, inferior humeral head injury resulting from impaction of the proximal humerus against the posterosuperior glenoid during posterior shoulder dislocation. It may be a notch or a wedge-like defect; there may be associated marrow edema if the posterior dislocation is acute. Fractures of the lesser tuberosity may also be present.
Posterior glenoid-sided failure associated with posterior dislocation includes the reverse Bankart lesion and its reverse variants. If there is a tear or avulsion of the posterior labrum and/or stripping of its posterior joint capsule, this is termed a “reverse Bankart lesion”. There is an associated fracture through the adjacent posterior bony glenoid in the “reverse bony Bankart”.
The inferior glenohumeral ligament (IGHL) is the primary static stabilizer of the glenohumeral joint. This most important stabilizer consists of an anterior band, a posterior band, and the axillary recess between. When the posterior band of the IGHL is torn away from its humeral attachment this is termed a “reverse humeral avulsion of the glenohumeral ligament” (“reverse HAGL”).
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Figure 1
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Figure 2
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References:
- Beltran J, Rosenberg ZS, Chandnani VP, Cuomo F, Beltran S, Rokito A. Glenohumeral instability: evaluation with MR Arthrography. RadioGraphics 1997; 17:373-378.
- Zlatkin, Michael B. MRI of the Shoulder. 2nded. Philadelphia, PA: Lippicott, Williams and Wilkins, 2003.
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