Imaging Glenohumeral Instability: What the General Radiologist Should Know

BACKGROUND

Due to its high mobility, the shoulder is the most unstable joint in the human body. Its instability is explained by a narrow glenohumeral joint contact surface, estimated at 30% of the humeral head (Fig. 1). Thus, this instability requires stabilizers that include both active (Fig. 2) and dynamic/passive (Fig. 3) elements (Table 1). Passive stabilizers are now often termed dynamic stabilizers due to the coordinated action of the muscles keeping the humeral head in the joint. The passive component of the musculature is actually only at the end range of motion when they are fully tightened. Imaging procedures for glenohumeral instability include plain film, CT (Figs. 4, 8) and MR arthrogram (Figs. 6, 7, 9-11).

Figure 1. Frontal left shoulder plain radiograph showing a narrow contact area (red line) between the humeral head and glenoid. This contact area represents about 30% of the humeral head surface which explains the joint instability.

Figure 2: A and B, Sagittal T1-weighted (A) and Sagittal proton density fatsat MR arthrogram (B) showing normal rotator cuff muscles which stabilize shoulder joint and consist of subscapularis (green arrow), supraspinatus (yellow arrow), infraspinatus (red arrow) and teres minor muscle (white arrow). The long head of the biceps is also seen (blue arrow).

Table 1. Table of active and passive shoulder stabilizers.

Figure 3: A and B, Sagittal (A) and axial (B) proton density fatsat MR arthrogram of the right shoulder demonstrates a normal labrum which is represented by a low signal intensity triangular structure (blue arrows).

Figure 4: Frontal and scapular Y-view of the left shoulder demonstrates an anterior dislocation with Bankart avulsion fracture (red arrow).

Anterior gleno-humeral dislocation (Fig. 4) is a frequent traumatic injury among the population and accounts for 90% of shoulder instability. It most commonly occurs in young patients. It is therefore important for general radiologists to become familiar with the imaging assessment and the semiology of an unstable shoulder.

Figure 5: Left shoulder CT in same patient as Figure 4 shows the Bankart fracture and the CT allows improved evaluation of the involved glenoid surface.

Figure 6: Arthrography of the left shoulder (A) with MR arthrogram (B) demonstrates the normal characteristic J-shaped axillary recess (green arrows).

Figure 7: A and B, Coronal (A) and axial (B) T2 fatsat MR images of the left shoulder with a region of edema of the humeral head corresponding to a Hill-Sachs lesion (yellow arrow).

Figure 8: Frontal and scapular-Y view of the left shoulder showing sequelae of anterior dislocation with Hill-Sachs deformity (yellow arrow) and Bankart fracture (red arrow).

Pathological bone lesions:

Bony lesions mainly include Hill-Sachs and Bankart fractures that are the results of an impaction. Hill-Sachs deformity (Figs. 7,8) is located in the posterior and lateral area of the humeral head. Bankart fracture corresponds to a fracture of the inferior rim of the glenoid (Figs. 5,8,9).

Table 2: Bankart lesions and main variants.

Figure 9: Axial proton density fatsat MR images shows a probable Bankart lesion (red arrow). However, an anterior labral periosteal sleeve avulsion (ALPSA) may have a similar appearance.

Figure 10: Humeral avulsion of the glenohumeral ligament (HAGL). Coronal proton density fatsat MR image of the left shoulder shows a humeral avulsion of the inferior gleno-humeral ligament (red arrow).

Figure 11: Anterior labral periosteal sleeve avulsion (ALPSA). Axial and coronal MR arthrogram images of the right shoulder show an avulsion of the antero-inferior labrum complex which is medially displaced (yellow arrows). Images courtesy of Phillip F. Tirman, MD

Pathological soft tissues lesions:

Soft tissues lesions are mainly due to labrum tears which can present several ways on MR arthrography (Table 2). Soft tissues lesions mainly include:

1) Bankart avulsion: corresponds to a complete avulsion of the inferior labrum complex (with tear of scapular periosteum) which can be associated with bone avulsion of the inferior glenoid (Fig. 9). This lesion is seen in 86% of patients after anterior gleno-humeral dislocation.

2) Perthes lesion: Consists of labral tear without scapular periosteum disruption

3) Humeral avulsion of the glenohumeral ligament (HAGL): corresponds to a glenohumeral ligament avulsion of its insertion on the humerus (Fig. 10).

4) Gleno-labral articular disruption (GLAD): consists of superficial antero-inferior labral tear with an associated anterior inferior glenoid articular cartilage injury.

5) Anterior labral periosteal sleeve avulsion (ALPSA): corresponds to a disruption of the antero-inferior labral complex which is medially displaced (Fig. 11).

Additional Reading:

1. Ruiz Santiago F, Martínez Martínez A, Tomás Muñoz P, Pozo Sánchez J, Zarza Pérez A. Imaging of shoulder instability. Quant Imaging Med Surg. 2017 Aug;7(4):422-433.

2. Sheehan SE, Gaviola G, Gordon R, et al. (2013). Traumatic shoulder injuries: a force mechanism analysis—glenohumeral dislocation and instability. American Journal of Roentgenology. 2013;201: 378-393.

3. Bencardino JT, Gyftopoulos S, Palmer WE, et al. Imaging in anterior glenohumeral instability. Radiology. 2013;269(2):323–337.

4. Vande Berg B, Omoumi P. Dislocation of the Shoulder Joint - Radiographic Analysis of Osseous Abnormalities. J Belg Soc Radiol. 2016 Nov 19;100(1):89.

5. Tirman PF, Palmer WE, Feller JF. MR arthrography of the shoulder. Magn Reson Imaging Clin N Am. 1997 Nov;5(4):811-39.

6. Grigorian M, Genant HK, Tirman PF. Magnetic resonance imaging of the glenoid labrum. Semin Roentgenol. 2000;35(3):277-285. doi:10.1053/sroe.2000.7337

7. Tirman PF, Steinbach LS, Feller JF, Stauffer AE. Humeral avulsion of the anterior shoulder stabilizing structures after anterior shoulder dislocation: demonstration by MRI and MR arthrography. Skeletal Radiol. 1996;25(8):743-748. DOI: 10.1007/s002560050172

8. Hottya GA, Tirman PF, Bost FW, Montgomery WH, Wolf EM, Genant HK. Tear of the posterior shoulder stabilizers after posterior dislocation: MR imaging and MR arthrographic findings with arthroscopic correlation. AJR Am J Roentgenol. 1998;171(3):763-768. DOI: 10.2214/ajr.171.3.9725313

9. Wischer TK, Bredella MA, Genant HK, Stoller DW, Bost FW, Tirman PF. Perthes Lesion (A Variant of the Bankart Lesion). AJR 2002; 178:233-237. DOI: 10.2214/ajr.178.1.1780233

Quoc Duy VO, MD is a Swiss physician and head of the Radiology Department at the Hospital of Morges (Ensemble Hospitalier de la Côte, Switzerland). He completed his undergraduate training in the University of Lausanne (UNIL) and his postgraduate Radiology Board Certification at the Hospital of Fribourg (Switzerland) where he worked for 2 years as Breast Imaging consultant. During this period, he was a core member of the Fribourg Breast Center where he took part in the cancer screening program. During the same period, he obtained a Swiss Diploma in Senology and a University Diploma in Breast Pathologies at the University of Saint-Quentin-en-Yvelines (Paris, France). He also perfected his skills in musculoskeletal radiology with a University Diploma in Musculoskeletal Imaging at the University of Montpellier (France). Over the years, Dr. Vo has also developed a great interest in healthcare management which motivated him to pursue a formal education in this field and to obtain a Diploma of Advanced Studies in Healthcare Management at the University of Geneva (UNIGE).