Introduction:
Acute shoulder injuries are common in female gymnasts, and uneven bars is the dominating mechanism of injury1. We present a case report of a conjoined tendon avulsion of both the latissimus dorsi (LD) and teres major (TM) muscles in a high-performance, middle-aged, veteran artistic gymnast. The challenges associated with these types of injuries are related to the complex anatomy, a potentially low degree of clinical suspicion because of unfamiliarity with the diagnosis among clinicians, and the fact that these injuries are not well visualized at standard shoulder imaging.
The LD and TM muscles act as one muscle unit in a wide variety of movements. The large LD muscle originates from the iliac crest´s posterior third, the sacrum, all lumbar vertebrae, the spinous processes of vertebrae T7-T12, and sometimes from the 9th to the 12th rib and the inferior angle of the scapula. It is oriented in a craniocaudal direction, dorso-laterally along the torso. The TM muscle originates from the scapular inferior angle. It follows the LD laterally and both muscles merge together to form a conjoined tendon and insert into the bicipital groove at the proximal humerus (Fig. 1a-c). The LD/TM muscle unit adducts, extends, and rotate the humerus internally when the shoulder is abducted. An intact LD muscle is mandatory for shoulder stability and plays a crucial role in stabilizing the lower back and the sacroiliac joint together with the contralateral gluteus maximus muscle during bodily motions like walking and running2,3. Together with the pectoralis major, the LD and TM are the main adductors of the shoulder4. A sudden contraction, against resistance, from a hyper-abducted position of the shoulder with the arm externally rotated and/or hyperextended can cause injury to the LD/TM muscle bellies, avulsion from their origins, or avulsion of the conjoined tendon insertion from the proximal humerus. Due to the rarity of injury to the LD and/or the TM, the literature mainly consists of case reports and case series of high-level athletes5. Latissimus dorsi tendon tears have been reported in baseball, cricket, weightlifting, soccer, water-skiing, wrestling, steer wrestling (rodeo event), cross-fit, and tennis5-14. Isolated teres major tendon tears have been reported in baseball6,7. Furthermore, reports of a combined tear to both the LD and the TM tendons are, to the best of our knowledge, restricted to baseball, golf, and water-skiing6,7,15,16. The incidence of LD tear seems to be increasing and the injury is predominantly found in baseball pitchers1. Because baseball is a sport with variable popularity around the world, injury to the LD/TM may be unfamiliar for physicians and physiotherapists in health care systems outside the Americas and South Asia. Consequently, the diagnosis may be overlooked, even in high quality health care countries. A clear classification system will be helpful when orthopaedic surgeons with limited knowledge of these injuries are consulted for treatment recommendations17.