Introduction 1 5 1 2 6 Table 1 Mnemonics for classification of glenohumeral instability TUBS AMBRII AIOS Traumatic Atraumatic Acquired Unidirectional Multidirectional Instability Bankart lesion Bilateral Overstress Surgery Rehabilitation Surgery  Inferior capsular shift   (Rotator) Interval closure  2 1 1 2 4 7 8 Table 2 1 2 4 Group Pathology Etiology Pattern of Lesions 1 Primary impingement Subacromial stenosis Rotator cuff lesions  No instability   2 Primary instability Repetitive microtrauma Labro-ligamentous lesions  Secondary impingement  Rotator cuff lesions    SLAP lesions    Posterosuperior impingement 3 Primary instability Generalized hyperlaxity Large capsular volume  Secondary impingement  Rotator cuff lesions    Labral abnormalities 4 Primary instability Acute trauma (dislocation) Labro-ligamentous injuries  No impingement  SLAP lesions Magnetic resonance (MR) imaging plays an important role in the diagnostic work-up of the painful athletic shoulder and with advanced techniques has in many instances already replaced diagnostic arthroscopy. This article discusses the role of MR imaging and MR arthrography in the context of the most common forms of sports-related glenohumeral instability and presents the typical MR arthrographic appearance of their corresponding intraarticular lesions and patterns of injury. Technical considerations 5 7 11 9 ab e r 1 5 9 12 Fig. 1a, b a b white arrow arrowheads black arrow ** T  The non-enhanced MR imaging protocol performed after acute shoulder dislocation includes a coronal oblique T1-weighted SE sequence, coronal oblique and transverse intermediate weighted TSE sequences with fat-saturation, and a sagittal oblique T2-weighted TSE sequence with the same geometric parameters as mentioned above. Traumatic glenohumeral instability 2 7 13 13 15 2 Labro-ligamentous injuries 14 16 19 20 7 9 14 21 22 8 9 7 9 14 23 26 7 14 27 28 5 16 8 26 2 Fig. 2a–f a b c d a l p s a e g l a d f h a g l LLC P HH AC IGHL  Bankart lesion 2 29 30 31 32 31 32 3 7 Fig. 3a–c a b arrows arrowheads c arrow arrowhead  Bony Bankart lesion 2 33 34 34 33 35 4 Fig. 4a–d a b arrowheads arrow c arrowhead ** ++ d C  Perthes lesion 2 27 31 36 14 27 12 27 5 Fig. 5a, b a arrow arrowhead b arrowhead arrow M  ALPSA lesion a l p s a 2 14 30 7 30 30 6 7 14 30 Fig. 6a, b a b arrows arrowheads  GLAD lesion g l a d 2 37 7 7 14 28 37 Fig. 7 arrow arrowhead  HAGL lesion h a g l 2 38 39 39 40 33 40 38 40 8 39 41 42 38 40 Fig. 8a, b a b arrowheads arrows *  14 33 38 43 14 9 14 Fig. 9 Nonclassifiable anteroinferior labro-ligamentous injury. Transverse T1-weighted MR arthrogram shows markedly deformed and enlarged labro-ligamentous complex without differentiability of labrum, IGHL, and scapular periosteum. The lesion was associated with chronic anteroinferior instability  Hill-Sachs defect 13 31 32 44 44 33 10 45 35 Fig. 10a–c a arrowhead b c b c b c arrowheads C  Atraumatic glenohumeral instability 1 2 35 46 1 2 6 46 2 11 2 Fig. 11a, b a b  Microtraumatic glenohumeral instability 4 7 9 35 46 s l a p 2 Posterosuperior glenoid impingement (PSI) 4 5 47 48 49 47 48 50 52 47 48 3 2 13 51 52 50 53 55 12 50 52 12 50 Fig. 12a–e a b c arrow a arrowhead b arrow c * a d e d white arrow black arrowhead black arrow white arrowhead e * arrowhead  SLAP lesions 55 56 degenerative fraying of the superior labrum; avulsion of the superior labrum and biceps anchor from the glenoid; bucket-handle tear of the superior labrum with preserved biceps anchor; 56 3 55 56 55 55 56 55 57 59 55 13 55 14 26 60 26 55 60 15 55 55 59 Fig. 13a–d 56 35 a b c d LBC HH G  Fig. 14 arrowhead * arrow  Fig. 15a–d a arrowhead b arrowheads c d arrows  Conclusion Sports-related glenohumeral instability is a complex and in many aspects still controversial subject. MR imaging can play an important role in evaluation of the athlete’s shoulder if it aims at providing essential information for therapeutic decisions at eye level with diagnostic arthroscopy. Therefore, the radiologist should be familiar with the mechanisms and classification of injuries as well as the advantages and limitations of his examination techniques. At present, MR arthrography represents the best evaluated and most informative imaging technique for the assessment of shoulder pathology in many aspects and thus, appears to be most valuable for the diagnostic work-up of glenohumeral instability and unclear shoulder pain in athletes.