Multi-modal imaging of the subscapularis muscle

Abstract

The subscapularis (SSC) muscle is the most powerful of the rotator cuff muscles, and plays an important role in shoulder motion and stabilization. SSC tendon tear is quite uncommon, compared to the supraspinatus (SSP) tendon, and, most of the time, part of a large rupture of the rotator cuff. Various complementary imaging techniques can be used to obtain an accurate diagnosis of SSC tendon lesions, as well as their extension and muscular impact. Pre-operative diagnosis by imaging is a key issue, since a lesion of the SSC tendon impacts on treatment, surgical approach, and post-operative functional prognosis of rotator cuff injuries. Radiologists should be aware of the SSC anatomy, variability in radiological presentation of muscle or tendon injury, and particular mechanisms that may lead to a SSC injury, such as coracoid impingement.

Teaching points: • Isolated subscapularis (SSC) tendon tears are uncommon. • Classically, partial thickness SSC tendon tears start superomedially and progress inferolaterally. • Long head of biceps tendon medial dislocation can indirectly signify SSC tendon tears. • SSC tendon injury is associated with anterior shoulder instability. • Dynamic ultrasound study of the SSC helps to diagnose coracoid impingement.

Keywords: Coracoid impingement; Magnetic resonance imaging; Rotator cuff; Subscapularis; Tendon injury.

Fig. 1

Anatomical views of the shoulder: front view (a), lateral oblique view (b). 1: Subscapularis muscle. 2: Subscapularis tendon. 3: long head of biceps tendon. 4: Coracoid process. 5: Teres major muscle. 6: Coraco-brachialis muscle. 7: Brachial plexus. 8: Lower subscapularis nerve. 9: Axillary artery

Fig. 2

Schematic representation of the rotator interval (RI): front view (a), sagittal view (b). The RI is bordered by the SSC tendon inferiorly (1) and the SSP tendon superiorly (2) and contains the intra-articular portion of LHBT (3). CHL (4) and SGHL (5) surround the LHBT in the RI, acting as a pulley system for LHBT stabilization

Fig. 3

B-mode ultrasound images of the SSC. a Transverse view (long axis) : the normal SSC tendon is hyperechoic compared to the adjacent muscle and has a fibrillary structure. b Sagittal view (short axis): multi-pennate structure of the SSC tendon with alternation of hypo and hyperechoic zones

Fig. 4

Calcific tendinitis of the SSC. Calcificationsof the SSC tendon (white arrows) overlap the lesser tuberosity in the front view in neutral rotation (a), are lateralized in external rotation (b), and medialized in internal rotation (c). On the Y view, calcifications of SSC tendon are seen under the coracoid process (white arrowhead) (d)

Fig. 5

Schematic representation of SSC tendon tears on magnetic resonance or computed tomography arthography. Normal SSC tendon (black arrowhead) (a). Incomplete partial thickness tear (white arrow) (b). Complete partial thickness tear (black arrow) associated with LHBT (white arrowhead) subluxation (c). Complete full thickness tear associated with LHBT (white arrowhead) dislocation and opacification of the SASD bursa (pin) (d)

Fig. 6

Computed tomography arthrography of the left shoulder with axial (a) and sagittal oblique (b) multiplanar reconstructions in a 38-year-old man, in a post-traumatic context. Isolated complete partial thickness tear of the SSC tendon, located at the articular side of the tendon, involving the upper fibres (arrow head), responsible for subluxation of the LHBT (arrow). Absence of contrast in the SASD bursa (pin) confirms the absence of transfixing or full thickness tear

Fig. 7

Forty-five-year old man with pain of the anterior shoulder. Computed tomography arthrography of the left shoulder with axial (a) and sagittal oblique (b) reconstruction. Complete partial thickness tear of the SSC tendon as shown by the absence of opacification of SASD bursa (pin), and the whole disruption of the tendon in the lateral direction (arrow head). The tendinous stump presents an intermediary retraction (arrow). This tear leads to a medial subluxation of the LHBT (black arrowhead) (a). Note that an intact superior glenohumeral ligament (black arrow) prevents the LHBT from inferior dislocation (b)

Fig. 8

Computed tomography athrography of the left shoulder with axial (a) and sagittal oblique (b) multiplanar reconstructions. Opacification of the SASD (pin) and whole disruption, either laterally (a) or vertically (b) (arrow heads) of the SSC tendon are consistent with a complete full thickness tear. Intermediate retraction of the tendinous stump (arrow)

Fig. 9

Axial (a) and sagittal oblique reformats (b) from a 3D FS T1-weighted MRA. Massive rotator cuff tear as shown by complete full thickness tears of the SSC (white arrow) (a) and the SSP (white arrow head) tendons (b). LHBT is medially dislocated (black arrow head) (a), and there is a proximal retraction of SSC tendon (black arrow)

Fig. 10

Axial FS T1 weighted MRA images (a, b, c) and axial oblique reformat through the LHBT (d). The inferior portion of the SSC tendon is normal (white arrow) (a), but there is an incomplete partial tear of the bursal side of the superior portion of the SSC tendon. This is responsible for a medial subluxation of the LHBT (black arrow head). Superiorly, the horizontal portion of the LHBT is hypertrophic (black arrow head), consistent with an “hourglass” biceps

Fig. 11

Left shoulder MRI of a 76-year-old woman. On axial FS PD-weighted images, the LHBT (white arrow heads) is medially displaced (a), and incarcerated into a cleavage of the SSC tendon (white arrow (b). On the sagittal oblique FS T2-weighted image (c), the SSC tendon tear (white arrow) is associated with a complete full thickness tear of the SSP tendon (black arrow head)

Fig. 12

Ultrasound (a) and computed tomography (CT) arthography (b) correlation: complete partial thickness tear of the upper SSC tendon responsible for subluxation of the LHBT (white arrow), located in front of the medial edge of the intertubercular sulcus. On CT-arthrography (b), contrast in the intertubercular groove is in direct continuity with intra-articular contrast, without any opacification of the SASD bursa (pin) because the bursal side of the transverse ligament is intact

Fig. 13

Sixty-two-year old man with a massive right rotator cuff tear involving the SSP, LHBT and SSC tendons. Transverse US image (a): exposure of the lesser tuberosity (white arrow heads) consistent with a complete full thickness tear of the SSC tendon. The intertubercular sulcus (white arrow) is empty because the LHBT is torn. Axial FS DP weighted MRI image (b): proximal retraction of the torn SSC tendon (black arrow). On sagittal T1 weighted MRI images (c) there is severe amyotrophy and fatty degeneration of the SSC muscle (white outline). On coronal FS DP weighted MRI images, there is an intermediate retraction of the torn SSP tendon (pin) (d). As the SSC tendon can no longer fulfil its stabilizing role, there is passive instability and an anterior sub-dislocation of the humeral head coming in contact with the coracoid process (lightning) (b). Also note an associated tear of the acromial head of the deltoid tendon (black arrow heads) (b, d)

Fig. 14

Schematic representations of surgical treatment of shoulder anterior instability: Bankart (a) and Latarjet (b) procedures

Fig. 15

Axial dynamic ultrasound images during progressive internal rotation of the shoulder (from a to d). Anatomic landmarks are the coracoid process (white arrow head), the lesser tuberosity (black arrow heads) and the intertubercular sulcus (black arrow). A macrocalcification is seen in the SSC tendon (arrow). It gradually approaches the coracoid process (b and c). In internal rotation (d), pain and sensation of projection under the probe when calcification passes under the coracoid process, are consistent with coracoid impingement (lightning) associated with calcific tendinitis

Fig. 16

Right shoulder MRI of a 21-year-old military serviceman with sharp pain of the right shoulder, occurring after military training. Axial (a) and coronal oblique (b) FS DP weighted images. Mottled and linear high signal areas in the SSC muscle mostly at the myotendinous junctions (white arrows) are secondary to intrinsic muscle lesions