A professional football player presents with posterior shoulder pain following a fall onto the anterior shoulder during a game. T2-weighted sagittal (1A), fat-suppressed proton density-weighted axial (1B,C) and fat-suppressed T2-weighted coronal images (1D) are provided. What are the findings? What is your diagnosis?
Findings compatible with posterior shoulder subluxation with an intramuscular tear of the teres minor, a posterior labral tear, and posterior capsular disruption.
Although rotator cuff tears have been extensively studied and are the focus of a multitude of publications in the scientific literature, the teres minor component of the cuff has received comparatively little attention. This is in part due to the fact that tears of the teres minor muscle or tendon are much less common than those of the supraspinatus, the infraspinatus, or the subscapularis. Teres minor tears have commonly been described in the context of large rotator cuff tears in which multiple other cuff tendons tear first.1 Alternatively, acute injuries of the teres minor are known to occur following posterior shoulder subluxation or dislocation, in which case concomitant injuries of the infraspinatus may be present.2,3 The teres minor muscle is also a site of a characteristic denervation injury at the shoulder, an entity in which our understanding of the process continues to evolve.
Anatomy and Function
The teres minor muscle works in tandem with the infraspinatus as an external rotator of the shoulder, and also assists in dynamic centering of the humeral head. It arises from the dorsal surface of the lateral border of the scapula. It has a relatively thin tendon that inserts upon the most inferior of the 3 facets of the greater tuberosity, where it is intimately associated with the posterior capsule.4 Muscle fibers of the teres minor also attach broadly to the proximal humerus caudal to the tendon insertion (Figure 3).
The teres minor muscle is innervated by a branch of the axillary nerve, which originates from the C5 and C6 components of the posterior cord of the brachial plexus. Within the shoulder, the axillary nerve travels posteriorly adjacent to the inferomedial joint capsule before passing through the quadrilateral space beside the posterior circumflex humeral artery. The quadrilateral space is a confined region bounded by the long head of the triceps muscle medially, the humeral shaft laterally, the teres minor muscle superiorly, and the teres major muscle inferiorly. After exiting the quadrilateral space, the axillary nerve typically courses around the surgical neck of the humerus and divides into anterior and posterior branches. The anterior branch supplies the anterior and middle deltoid muscle. The posterior branch courses along the inferior glenoid rim before dividing into the upper lateral brachial cutaneous nerve and the nerve to the teres minor.5 The nerve to the teres minor courses medially along the posteroinferior glenoid rim before entering the inferior aspect of the muscle (Figure 4). Considerable anatomic variations in the course of the axillary nerve and its branching patterns have been observed.6 For example the axillary nerve may branch anterior to, within, or posterior to the quadrilateral space, and the length of the branch to the teres minor varies. Certain anatomical variations may result in greater risk for denervation injury to the teres minor muscle.
MRI appearance of teres minor tears
Tears of the teres minor are known to occur in the setting of massive rotator cuff tears, defined as tears greater than 5cm in size7 or as complete cuff tears of at least 2 tendons.8 Massive rotator cuff tears are known to alter the normal biomechanics of the shoulder, as the rotator cuff muscles act as force couples to restrain an inherently unstable glenohumeral joint. As rotator cuff tendons tear, most commonly beginning with the supraspinatus, the remaining tendons of the cuff are placed under an increasing tensile load which can result in tear propagation.9 When massive cuff tears involve the teres minor, the tear may be found in the context of chronic tears of other tendons leading to a stress-induced tear of the teres minor, or the injury may be the result of severe acute trauma sufficient to result in tears of multiple cuff tendons (Figure 5).
Of traumatic causes for a teres minor tear, anterior shoulder dislocations are a well-known etiology, typically seen in patients older than 40 who fall on an outstretched hand.10 In such cases where the teres minor tears, injuries to multiple other structures within the shoulder are typically encountered (Figure 6).
Although posterior shoulder dislocation is much less common than anterior dislocation, and though posterior instability has considerably less study in the literature, the association between posterior dislocation and teres minor tears is well established. Ovesen and Sojbjerg’s cadaveric study in 1986 revealed tears of the teres minor and the posterior capsule in 10/10 specimens following posterior dislocation.11 Previous studies of the shoulder following posterior dislocation have noted injuries to the teres minor, the infraspinatus, and the posterior capsule (Figure 7). In our experience at Radsource, teres minor injuries following posterior subluxation or dislocation are frequently seen in the absence of other cuff pathology. Posterior capsular tears are often found in this setting (Figure 8).
Denervation injuries of the teres minor
In contrast to the relatively rare tears of the teres minor muscle or tendon, denervation injuries of the teres minor are relatively common, found in 3-5% of patients undergoing routine MRI of the shoulder12,13 Denervation of muscle is identified on MR images initially by the presence of diffuse, homogeneous muscle edema. Later in the process, fatty infiltration occurs and when denervation is longstanding complete fatty atrophy of the teres minor may be present.
Classically, denervation of the teres minor found on MR imaging has been attributed to quadrilateral space syndrome.14 This syndrome, first reported by Cahill and Palmer in 198315, was described as a relatively rare condition caused by compression of the axillary nerve within the confined anatomical region known as the quadrilateral space (Figure 4). It is felt to occur primarily in young athletes without prior trauma. Patients present with poorly localized shoulder pain exacerbated by abduction and external rotation.16 Point tenderness may be present over the teres minor. The cause of compression is thought to be most commonly due to fibrous bands which form within the quadrilateral space, perhaps due to repetitive microtrauma from overhead motion such as throwing.17 In cases of quadrilateral space syndrome due to fibrous bands, MR images typically do not identify the bands. At times, however, space occupying lesions resulting in nerve compression within the quadrilateral space are identified (Figures 9,10).
Although it is classically felt that quadrilateral space syndrome should result in denervation changes of both the teres minor and the deltoid muscles, in reality isolated teres minor denervation is often found, even in classic examples such as Figure 9 in which a compressing lesion is present within the quadrilateral space. In cases such as this one, the lack of deltoid denervation is presumably related to variations in the branching pattern of the axillary nerve. In other cases, however, it is increasingly recognized that teres minor denervation can exist as an entity entirely distinct from quadrilateral space syndrome. It is felt that the axillary nerve branch to the teres minor can be injured in isolation due in part to its vulnerable course along the joint capsule and the inferior glenoid rim.
Trauma may cause acute traction injury to the nerve, or glenohumeral instability may result in damage to the nerve from repetitive microtrauma (Figure 11). Damage to the nerve to the teres minor due to humeral head decentering may occur in the young athlete, particularly those who participate in overhead sports. It may also be found in older patients with glenohumeral decentering due to rotator cuff tears, labroligamentous tears, or osteoarthritis. The latter category do not fit the expected demographic for quadrilateral space syndrome. Chafik’s cadaveric study of 31 shoulders revealed a consistent fascial sling about which the nerve to the teres minor travels.18 He postulated that the angulation of the nerve about this fascial sling results in a potential site for compression and tethering, perhaps accounting for the prevalence of isolated teres minor denervation.
From a practical standpoint, when we encounter denervation of the teres minor on MR studies, we no longer describe these cases as “quadrilateral space syndrome”. We simply note the severity and acuity of the denervation and commonly add that “no compressing lesion is seen along the course of the axillary nerve”.
When the teres minor is torn in the context of a massive rotator cuff tear, numerous treatment options are available, including non-operative management, arthroscopic debridement, partial or complete repair, superior capsular reconstruction, muscle and tendon transfers, and reverse total shoulder arthroplasty. Isolated tears of the teres minor are typically managed conservatively, as many of these injuries are intramuscular and respond well to conservative management. Lee, however, reported good results in a single case of arthroscopic treatment of an isolated teres minor tear in a patient with persistent severe pain 4 months after injury.19 Because isolated teres minor tears often occur in the context of posterior shoulder dislocation or subluxation, surgery may also be performed to address associated tears of the posterior labrum and shoulder capsule.
In patients with teres minor denervation, initial management is generally conservative, consisting of analgesics, physiotherapy, and avoidance of aggravating athletic activities.20 Surgery is contemplated for those who do not respond to conservative therapy or in patients that have a space occupying lesion along the course of the axillary nerve.21 The majority of reports related to treatment of teres minor denervation relate to quadrilateral space syndrome, with numerous surgeons describing lysis of fibrous bands within the quadrilateral space. The more recently described entity of isolated teres minor atrophy is thought to be secondary to injury of the nerve to the teres minor beyond the quadrilateral space. Kruse et al. described successful treatment of 22 patients with this entity in which open release of the fascial sling enveloping the nerve branches to the teres minor was performed.22
The teres minor is the component of the rotator cuff least likely to tear. Injuries to the teres minor typically occur either in the setting of massive rotator cuff tears or following posterior subluxation/dislocation. Denervation injury of the teres minor is a much more common event, classically thought to be due to quadrilateral space syndrome but now recognized as also occurring as a distinct entity in which the nerve to the teres minor is injured beyond the quadrilateral space. MRI is an effective means to evaluate both tears and denervation injuries of the teres minor, allowing detection of associated abnormalities of the capsule and labrum in cases of teres minor tears, and visualizing muscle edema, fatty atrophy, and potential masses in cases of denervation.
- Shetty M, Yadavalli S, Khan F, Wiater JM, Fessell DP Teres Minor Tendon Tears: MR Imaging and Clinical Implications. AJR 2006; 186: Number 4 supplement. ↩
- Hottya GA, Tirman FJ, Bost FW et al. Tear of the Posterior Shoulder Stabilizers After Posterior Dislocation: MR Imaging and MR Arthrographic Findings with Arthroscopic Correlation. AJR:171, September 1998 ↩
- Cain EL, Andrachuk J, Wilk KE. Traumatic Full-Thickness Infraspinatus and Teres Minor Tendon Tears. J Orth and Sports Physical Therapy 2013; 43:8. ↩
- DePalma AF, Brand RA. Surgical Anatomy of the Rotator Cuff and the Natural History of Degenerative Periarthritis. Clin Orthop Relat Res. 2008 Mar; 466(3): 543–551. ↩
- Safran M. Nerve injury about the shoulder in athletes, part 1. Suprascapular nerve and axillary nerve. AJSM 2004; 32(3): 803-819. ↩
- Friend J, Francis S, McCulloch J et al. Teres minor innervation in the context of isolated muscle atrophy. Surg Radiol Anat 2009, December. ↩
- DeOrio JK, Cofield RH. Results of a second attempt at surgical repair of a failed initial rotator-cuff repair. J Bone Joint Surg Am 1984;66: 563-7. ↩
- Gerber C, Fuchs B, Hodler J. The results of repair of massive tears of the rotator cuff. J Bone Joint Surg Am 2000;82:505-15 ↩
- Greenspoon JA, Petri M, Warth RJ, and Millett PJ. Massive rotator cuff tears: pathomechanics, current treatment options, and clinical outcomes. J Shoulder Elbow Surg (2015), 1-13. ↩
- Atef A, El-Tantawy A, Gad H, Hefeda M. Prevalence of associated injuries after anterior shoulder dislocation: A prospective study. Int Orthop. 2016;40(3):519–524. ↩
- Jörgen Ovesen & Jens Ole Söjbjerg (1986) Posterior shoulder dislocation: Muscle and capsular lesions in cadaver experiments, Acta Orthopaedica Scandinavica, 57:6, 535-536. ↩
- Wilson L, Sundaram M, Piraino DW et al. Isolated teres minor atrophy: manifestation of quadrilateral space syndrome or traction injury to the axillary nerve? Orthopedics. 2006 May;29(5):447-50. ↩
- Solka CM, Lin J, Feinberg J, Potter HG. Teres minor denervation on routine magnetic resonance imaging of the shoulder. Skeletal Radiol. 2004 Sep;33(9):514-8. ↩
- Linker CS, Helms C, Fritz RC. Quadrilateral Space Syndrome: Findings at MR Imaging. Radiology 1993; 188:675-676. ↩
- Cahill BR, Palmer RE. Quadrilateral space syndrome. J Hand Surg Am 1983; 8:65–69. ↩
- Yanny S, Toms AP. MR Patterns of Denervation Around the Shoulder. AJR 2010; 195:W157–W163. ↩
- Redler MR, Ruland LJ 3rd, McCue FC 3rd. Quadrilateral space syndrome in a throwing athlete. Am J Sports Med 1986; 14:511–513. ↩
- Chafik D, Galatz LM, Keener JD, et al. Teres minor muscle and related anatomy. J Shoulder Elbow Surg (2013) 22, 108-114. ↩
- Lee S, Park S, Park M, Ji J. Arthroscopic Treatment of Isolated Teres Minor Tendon Tear: A Case Report. Clinics in Shoulder and Elbow Vol. 18, No. 3, September, 2015. ↩
- Francel TJ, Dellon AL, Campbell JN. Quadrilateral space syndrome: diagnosis and operative decompression technique. Plast Reconstr Surg1991;87:911–16. ↩
- Lester B , Jeong GK, Weiland AJ, et al. Quadrilateral space syndrome: diagnosis, pathology, and treatment. Am J Orthop 1999;28:718–22, 725. ↩
- Kruse LM, Yamaguchi K, Keener JD, Chamberlain AM. Clinical Outcomes Following Decompression of the Nerve to the Teres Minor in Patients with Idiopathic Isolated Teres Minor Fatty Atrophy. J Shoulder Elbow Surg. 2015 April; 24(4): 628–633. ↩