Insights Imaging (2016) 7:779–791 DOI 10.1007/s13244-016-0526-1 REVIEW Multi-modal imaging of the subscapularis muscle Mona Alilet1 & Julien Behr2 & Jean-Philippe Nueffer1 & Benoit Barbier-Brion 3 & Sébastien Aubry 1,4 Received: 31 May 2016 /Revised: 6 September 2016 /Accepted: 28 September 2016 /Published online: 17 October 2016 # The Author(s) 2016. This article is published with open access at Springerlink.com Abstract • Long head of biceps tendon medial dislocation can indirect- The subscapularis (SSC) muscle is the most powerful of the ly signify SSC tendon tears. rotator cuff muscles, and plays an important role in shoulder • SSC tendon injury is associated with anterior shoulder motion and stabilization. SSC tendon tear is quite uncom- instability. mon, compared to the supraspinatus (SSP) tendon, and, most • Dynamic ultrasound study of the SSC helps to diagnose of the time, part of a large rupture of the rotator cuff. coracoid impingement. Various complementary imaging techniques can be used to obtain an accurate diagnosis of SSC tendon lesions, as well Keywords Subscapularis . Tendon injury . Rotator cuff . as their extension and muscular impact. Pre-operative diag- Magnetic resonance imaging . Coracoid impingement nosis 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. Introduction Radiologists should be aware of the SSC anatomy, variabil- ity in radiological presentation of muscle or tendon injury, The subscapularis (SSC) muscle is one of the four compo- and particular mechanisms that may lead to a SSC injury, nents of the rotator cuff along with the supraspinatus (SSP), such as coracoid impingement. infraspinatus, and teres minor muscles. The long head of bi- ceps (LHB) tendon is classically associated. Teaching Points The muscles of the rotator cuff and their tendinous inser- • Isolated subscapularis (SSC) tendon tears are uncommon. tions play an important role in shoulder stability, and in the • Classically, partial thickness SSC tendon tears start motion of the glenohumeral joint. The SSC in particular has superomedially and progress inferolaterally. the greatest force-producing capacity, followed by the infraspinatus, SSP, and teres minor [1]. Rotator cuff pathologies are very common, and foremost among these are SSP tendon tears. SSC tendon pathology is * Sébastien Aubry [email protected] quite uncommon, and most of the time, occurs as part of a larger rupture of the rotator cuff. 1 Department of Musculoskeletal Imaging, CHRU de Besançon, In cadaveric studies, the prevalence of SSC tendon tears CHRU Jean Minjoz, Boulevard Fleming, 25030 Besançon varies between 29 and 37 % [2], whereas it is estimated to Cedex, France be between 5 and 27 % in clinical studies [3, 4]. This dis- 2 Anatomy Laboratory, University of Franche-Comte, crepancy could be related to the incomplete visualization of Besançon, France the SSC tendon on both arthroscopy and open surgery [5]. 3 Groupe CIMRAD, Centre d’imagerie des Tilleroyes, Pre-operative diagnosis of SSC tendon tears is therefore a Besançon, France major issue, especially since a lesion of the SSC tendon will 4 Nanomedicine and Imagery Laboratory, EA4662, University of have an impact on treatment, surgical approach, and post- Franche-Comte, Besançon, France operative functional prognosis [6]. The purposes of this 780 Insights Imaging (2016) 7:779–791 article are to describe the normal appearance of the SSC, and Function to review the imaging findings encountered in patients with lesions of the SSC tendon and muscle, according to specific The principal role of the SSC muscle in shoulder motion is pathophysiological mechanisms. internal rotation. In variable positions, the superior subscapularis fibres assist in abduction, while the inferior fi- bres assist in adduction. At the beginning of elevation shoul- der movement, EMG onset of the upper portion of the SSC Anatomy occurs first, which increases the glenohumeral congruence. The upper SSC also demonstrates higher levels of activation The SSC muscle is the largest and the most powerful of the than the lower portion, which confirms the hypothesis of a rotator cuff muscles. It is located in the subscapular fossa at participation in abduction [8]. the anterior aspect of the scapula. It contains multiple tendi- The SSC muscle provides active stabilization of the shoul- nous and muscular bundles that merge laterally into a flattened der during external rotation and flexion [9]. Its action is coor- tendon in the upper two-thirds of the muscle. This tendinous dinated with the other muscles of the rotator cuff to ensure portion has a variable insertion, mostly on the lesser tuberosity shoulder function and the centring of the humeral head in the of the humerus, but also on the greater tuberosity and the glenoid fossa. There are balanced forces between the superior bicipital groove [2]. SSC tendon fibres contained within a fibres of the SSC and its antagonist, the infraspinatus muscle, fibrous expansion from the pectoralis major tendon form the in the axial plane. Conversely, the inferior fibres of the SSC transverse ligament, which is a fascia covering the vertical resist, in the coronal plane, the elevation of the humeral head portion of the LHBT (Fig. 1). induced by the deltoid muscle [2]. The lower third of the muscle has a muscular attachment The SSC muscle also plays a role in passive stability of the onto the inferior part of the lesser tuberosity and onto the glenohumeral joint, resisting anterior luxation. Indeed, anteri- anterior aspect of the humeral diaphysis. or luxation is associated with laxity of the lower portion of the SSC muscle [10]. This explains why some authors recom- mend surgical repair of the SSC for treatment of anterior Innervation glenohumeral instability [11]. Also, the SSC tendon stabilizes the LHBT within the rotator interval (see below). Variants of the innervation of the SSC muscle are common [7]. Classically, the two superior thirds and the inferior third of the SSC muscle are innervated, respectively, by the upper and low- Anatomical relations er subscapularis nerves, which are both branches of the poste- rior chord of the brachial plexus (Fig. 1). Electromyographic Rotator interval (EMG) studies have shown differences in activity between the upper and lower portion of the SSC muscle, suggesting that The SSC tendon contributes to the formation of an anatomical they work as two different muscular units during voluntary space located in the anterosuperior portion of the shoulder, shoulder movements [8]. called the rotator interval (Fig. 2), which is a tendinous gap in 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 Insights Imaging (2016) 7:779–791 781 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 the rotator cuff, exclusively covered by capsular tissue. It is a and the superior glenohumeral ligament (SGHL). The triangular shaped space bordered inferiorly by the superior free inferomedial CHL, the SGHL and the superior fibres of the edge of the SSC tendon, and superiorly by the anterior free SSC tendon unite in the lateral rotator interval and act as a edge of the SSP tendon. The base of this triangle is formed pulley system for the LHBT, which is a key element for stabi- by the coracoid process medially, and its apex is the lization of the LHBT [13]. Indeed, this pulley system prevents intertubercular sulcus laterally [12]. The anterior aspect of the inferior luxation of the horizontal portion of the LHBT, and rotator interval is formed by a fibrous capsule made of blended medial luxation of its vertical portion. The most superior inser- fibres coming from the SSC and SSP tendons. It is reinforced tion point of the SSC could be the most important structure for by two ligaments, namely the coracohumeral ligament (CHL) medial stabilization of LHBT [14]. 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 782 Insights Imaging (2016) 7:779–791 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) Other anatomical relations tear is painful during development, whereas a constituted tear is less painful, if at all. When subacromial-subdeltoid (SASD) The origin of the vascular-nervous pedicle of the upper limb is bursitis is associated, pain is common. Calcific tendinitis can located at the anterior aspect of the SSC muscle. The axillary also be painful, especially when hydroxyapatite calcifications artery and vein, and the chords of the brachial plexus lean on are in the resorptive phase [17]. the SSC muscle. In front of the SSC muscle, the medial, lateral Most of the time, clinical examination can orientate to- and posterior chords of the brachial plexus divide into their wards an articular or periarticular pathology, but it cannot terminal branches (Fig. 1). identify the precise topography or the pathological mecha- Among the anatomical variations of the shoulder, an acces- nism, even if there are many clinical tests [18].