Clinical History: A 20 year-old professional baseball pitcher presents with axillary pain. (1a) Oblique coronal fat suppressed T2-weighted and (1b) sagittal T2-weighted and (1c) axial fat suppressed proton density-weighted images are provided. What are the findings? What is your diagnosis?
Acute musculotendinous tears of the latissimus dorsi and teres major.
Latissimus dorsi and teres major muscle and tendon tears are relatively rare injuries, with a handful of case reports in the literature, and only a few published studies on management of the injury, focusing on elite athletes. The injury can occur as an acute traumatic incident or a more insidious strain, or may present as a pseudo-mass. The patient may be referred for shoulder MRI to rule out rotator cuff or labral pathology. The latissimus dorsi and teres major muscles are only partially included in the field of view of typical shoulder MRI, and therefore, the radiologist must possess an understanding of the anatomy, and check that the muscles are normal in appearance on every shoulder MRI.
Anatomy and Function
The latissimus dorsi (from the Latin meaning broadest muscle of the back) is a large fan shaped muscle taking origin from the spinous processes of T7-L5, the thoracolumbar fascia, the iliac crest, the most inferior 3 to 4 ribs, and the inferior angle of the scapula (Figure 5). From this extensive origin the superior muscle fibers pass horizontally, the mid fibers obliquely superolaterally, and the inferior fibers extend nearly vertically, until all converge to form a thick fasciculus which passes over the inferior angle of the scapula. The muscle then curves around the lower border of the teres major muscle and twists upon itself, so that the superior fibers become posterior and then inferior, and the inferior fibers become anterior and then superior.
It terminates in a 7 cm long tendon which passes anterior to the teres major with which it is intimately associated, separated at the insertion by a bursa1. One anatomical study describes the teres major tendon inserting into the tendon of the latissimus dorsi proximal to their insertion in a majority of specimens studied2.
The latissimus dorsi tendon inserts into the bottom of the intertubercular groove of the humerus, just anterior and lateral to the teres major tendon insertion, and medial to the pectoralis major insertion (Figure 6).
The latissimus dorsi is innervated by the thoracodorsal nerve. It adducts, extends and internally rotates the arm. The teres major muscle arises from the dorsal surface of the inferior angle of the scapula and from the fibrosed septa between the teres major muscle and the teres minor and infraspinatus. The fibers course upward and laterally, ending in a flat tendon, 5cm long, inserting into the lesser crest of the lesser tubercle of the humerus, medial to the latissimus dorsi tendon. The teres major is innervated by the lower subscapular nerve. Like the latissimus dorsi, it serves to internally rotate and adduct the humerus. Because of the intimate relation between the latissimus dorsi and the teres major, it is often difficult to distinguish the two muscle bellies and tendons on coronal MRI images, but the latissimus dorsi is the more caudal of the two muscles. On sagittal images, the latissimus dorsi tendon is visible coursing anteriorly, and the teres major muscle is visible posterior to it, inferior to the quadrilateral space (Figure 7). On axial images the pectoralis major tendon serves as a landmark, such that the latissimus dorsi tendon and teres major tendons can be identified medially on the same axial image. Often the teres major tendon and latissimus dorsi tendon become confluent proximal to their insertion, so the teres major tendon is not identifiable as a discrete linear structure like the latissimus dorsi and pectoralis major (Figure 8). Because of the similar functions of the latissimus dorsi and teres major muscles, an injury often affects both muscles or tendons.
Injury mechanism and clinical presentation
Acute avulsion of the latissimus dorsi from its humeral insertion occurs with forceful resisted arm adduction. The patient reports immediate pain, often accompanied by a tearing sensation. There may be a tender palpable mass in the posterior axillary region. Point tenderness over the humeral insertion may be present. If the injury occurs with insidious onset due to repetitive stress, the patient may not recall the inciting events and will instead present with a chronic painful torn muscle mass or “pseudotumor”, which can be mistaken for malignancy. The concomitant finding on x-ray of cortical abnormality at the humeral avulsion site can also be mistaken for malignancy3.
Latissimus dorsi tears have been reported associated with specific sports activities, such as water skiing, golf, baseball pitching, rock climbing, volleyball and gymnastics. Water skiing injuries occur as acute traumatic events. The largest series reported have been in the study of injuries to professional baseball pitchers, in whom this injury is far more common than in the general population. The player typically presents with acute pain in the upper arm and posterior axilla, with symptoms most severe during ball release and follow-though. Most commonly there are no pre-existing symptoms related to the latissimus dorsi, but cases of vague posterior tightness and fatigue have been reported leading up to the point of incapacitating injury, subsequently documented to be a latissimus dorsi avulsion4. The latissimus dorsi and teres major muscles have been shown through electromyographic analysis to be very active in the late cocking phase of the pitch, continuing throughout acceleration, and moderately active in follow-though as well5. The stresses placed on the muscles are understandably much greater in professional pitchers as compared to amateurs6. Furthermore, although not yet documented, it has been speculated that pre-existing injuries in professional pitchers may place even higher stresses on latissimus dorsi and teres major muscles, which may be acting to compensate for a glenohumeral internal rotation deficit (GIRD)7. Electromyographic studies have revealed marked activity of the latissimus dorsi and teres major muscles in golf during the acceleration phase of the golf swing, and moderate activity during the forward swing and follow through8. A case report describes a novice golfer with avulsions of the latissimus dorsi and teres major tendons after several days of playing an unusually large amount of golf9. In golf associated latissimus dorsi tears, the target-side shoulder is affected (the left shoulder in a right-handed golfer).
One case report describes the successful surgical repair of an acute latissimus dorsi tendon avulsion in a competitive water skier. The patient was able to return to competitive slalom waterskiing, which places extreme demands upon the latissimus dorsi muscle, especially in returning from the fully abducted “stretched out” slalom position10. More recently, two larger series have described the successful conservative treatment of latissimus dorsi/teres major tears in professional baseball pitchers. Management consisted of rest followed by general strengthening exercises as tolerated and a gradual stepwise progression back to throwing. The vast majority of major league pitchers were able to return to pitching at or above the level they were previously playing4, but in many cases tendon avulsion was considered a season ending injury, since they could not return to play for 3 or 4 months7. In this Web Clinic case our pitcher was treated non-operatively, and returned for follow-up imaging 5 months later, when MRI of the shoulder revealed complete healing of the muscle tears (Figure 9).
In this month’s case, the clinical history of axillary pain caused the MR technologist to scan more caudally than in a typical shoulder MR, and thus the injury was clearly demonstrated. However, the more typical occurrence is a less obvious clinical presentation of vague pain which is referred for shoulder MR to rule out the far more common pathology of rotator cuff tear or labral tear. Another patient presented with a classic history of acute trauma while water-skiing, with a ripping sensation and axillary pain. The referring physician suspected a latissimus dorsi tear, and ordered an MR of the proximal humerus. A shoulder MR was also ordered, to evaluate more proximal pain. Comparison of both studies obtained the same day on this patient shows that, even with a relatively extensive tear demonstrated on the humerus MRI, the pathology is barely visible near the edge of the FOV on the shoulder study (see Figure 10).
Latissimus dorsi tears can present with pain following recent trauma, or as a chronic injury in the form of a pseudomass. Another cause of muscle edema within the latissimus dorsi is an acute denervation injury. The following case is of a patient who presented with shoulder pain, but no known injury (Figures 11 and 12).
In this case, diffuse edema involving the entire muscle with preservation of normal muscle architecture, and no evidence of tendon or muscle retraction, are findings suggesting acute denervation injury rather than trauma. A follow-up MR obtained at an outside facility demonstrated complete resolution of muscle edema (personal communication with referring physician), and work-up is now focusing on a proximal location of compression of the thoracodorsal nerve or its components.
Although relatively rare in the general population, latissimus dorsi and teres major tears do occur, and are seen not uncommonly in the high level throwing athlete. If the history and physical examination suggest the possible diagnosis of latissimus dorsi/teres major injury, the field of view on MR imaging should be expanded to include as much of the muscles as possible, as well as their humeral insertions in the axial plane. If, as is commonly the case, the diagnosis is not suspected, and a normal shoulder study is ordered, it is incumbent upon the radiologist to identify included portions of the latissimus dorsi and teres major muscles and tendons, to rule out injury. Diffuse muscle edema involving the entire muscle with preservation of normal muscle and tendon morphology are signs suggestive of acute denervation injury as opposed to a muscle tear. More chronic muscle injury may present as a pseudomass, and recognition of distorted anatomy of the latissimus dorsi and teres major muscles will be important to make the correct diagnosis of a benign entity that can be treated non-operatively.
1 Gray, Henry. Anatomy of the Human Body. Philadelphia: Lea & Febiger, 1918; Bartleby.com, 2000. www.bartleby.com/107/.
2 Morelli M, Nagamori J, Gilbart M, MiniaciA. Latissimus Dorsi Tendon Transfer for Massive Irreparable Cuff Tears: an Anatomic Study. J Shoulder Elbow Surg. 2008:17 (1): 139-143.
3 Anderson SE, Hertel R, Johnston JO, Stauffer E, Leinweber E, Steinbach LS. Latissimus Dorsi Tendinosis and Tear: Imaging Features of a Pseudotumor of the Upper Limb in Five Patients. AJR 2005 (185): 1145-1151.
4 Schickendantz MS, Scott GK, Meister K, Lund P, Berverly L. Latissimus Dorsi and Teres Major Tears in Professional Baseball Pitchers: A Case Series. American J Sports Med. 2009 (37): 2016-2020.
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