Radiographic and Advanced Imaging Evaluation of Posterior Shoulder Instability

Abstract

Purpose of review: Posterior shoulder instability is an uncommon but important cause of shoulder dysfunction and pain which may occur as the result of seizure, high energy trauma, or repetitive stress related to occupational or sport-specific activities. This current review details the imaging approach to the patient with posterior shoulder instability and describes commonly associated soft tissue and bony pathologies identified by radiographs, CT, and MR imaging.

Recent findings: Advances in MR imaging technology and techniques allow for more accurate evaluation of bone and soft tissue pathology associated with posterior shoulder instability while sparing patients exposure to radiation. Imaging can contribute significantly to the clinical management of patients with posterior shoulder instability by demonstrating the extent of associated injuries and identifying predisposing anatomic conditions. Radiologic evaluation should be guided by clinical history and physical examination, beginning with radiographs followed by CT and/or MRI for assessment of osseous and soft tissue pathology. Synthesis of a patient's clinical history, physical exam findings, and radiologic examinations should guide clinical management.

Keywords: MR imaging; POLPSA; Posterior shoulder instability; Reverse Bankart; Shoulder.

Fig. 1

Axial T2FS MR image (A) shows normal dark triangular appearance of intact posterior labrum (white arrow). Axial T1FS MR arthrogram image (B) shows the anterior (white arrowhead) and posterior (black arrowhead) bands of the inferior glenohumeral ligament. Axial CT arthrogram image (C) shows intact AIGHL (white arrowhead), PIGHL (black arrowhead), and posterior labrum (white arrow)

Fig. 2

Sagittal CT image demonstrates measuring the extent of glenoid bone loss in the setting of a reverse bony Bankart using the best-fit-circle method, which superimposes a circle over the glenoid articular surface. The defect size (b) divided by the glenoid diameter (A) equals the percentage of glenoid bone loss

Fig. 3

Axillary radiograph (A), axial CT (B), and axial T2 fat-saturated MR (C) images demonstrate a reverse bony Bankart lesion (arrow) and a reverse Hill-Sachs impaction fracture (arrowhead). Sagittal T2 fat-saturated image (D) demonstrates the extent of the reverse bony Bankart lesion (bracket). Additionally, there is posterior subluxation of the humeral head relative to the glenoid (B and C)

Fig. 4

Axillary radiograph (A), axial CT (B), and axial T2 fat-saturated MR (C) images demonstrate glenoid dysplasia with associated overgrowth of the posterior glenoid cartilage best seen on MR (arrow)

Fig. 5

Axial CT image demonstrates glenoid retroversion measuring 15° in the setting of glenoid dysplasia. By creating a line through the scapular axis (arrowhead), glenoid version can be measured as the angle between the glenoid articular surface and a line perpendicular to the scapular axis

Fig. 6

Axial CT images utilizing best-fit-circle method to quantify alpha angle (A), gamma angle (B), and defect depth measurement measured as a dotted line (C)

Fig. 7

Axial PD (A) and T2 fat-saturated (B) MR images demonstrate a reverse Bankart lesion (arrow) in the setting of posterior glenoid dysplasia (arrowhead)

Fig. 8

Axial (A) and sagittal (B) T2 fat-saturated MR images demonstrate a tear of the posteroinferior chondrolabral junction (arrow) with associated stripping of the posterior glenoid periosteum (arrowhead) consistent with a posterior labrocapsular periosteal sleeve avulsion lesion. The extent of periosteal stripping (bracket) is well seen in the sagittal plane

Fig. 9

Axial T2 fat-saturated MR image demonstrates posterior decentering of the humeral head relative to the glenoid, subtle incomplete tear (“marginal crack”) of the posterior chondrolabral junction (arrow), and a cyst-like fluid collection between the glenoid and deep labrum (arrowhead) consistent with Kim’s lesion

Fig. 10

Axial T2 fat-saturated MR arthrogram image demonstrates a tear of the posteroinferior glenoid labrum (black arrow) with an associated articular cartilage defect (white arrow) consistent with posterior glenolabral articular disruption. Additionally, there is attritional bone loss of the posteroinferior glenoid (arrowhead)

Fig. 11

Axial T2 fat-saturated MR image demonstrates a full-thickness tear of the posterior band of the inferior glenohumeral ligament from its humeral attachment (arrow) with associated extracapsular joint fluid along the PIGHL (arrowhead) consistent with a posterior humeral avulsion of the inferior glenohumeral ligament

Fig. 12

Axial PD MR image demonstrates a functional full-thickness tear of the posterior band of the inferior glenohumeral ligament, which is lax or “wavy” (arrow), associated avulsive fragment (arrowhead) from the humerus, and extracapsular joint fluid (asterisk) consistent with a bony posterior humeral avulsion of the inferior glenohumeral ligament

Fig. 13

Axillary view radiograph (A), axial CT (B), and axial PD MR images (C) demonstrate a small curvilinear focus of ossification along the posterior glenoid consistent with a Bennett lesion (arrow). Arthroscopic images of the same patient before (D) and after (E) debridement of the lesion