Discussion:
Injury to the latissimus dorsi muscle is rare in non-baseball-athletes and most often occurs after an acute traumatic event, typically as an avulsion of the tendon rather than injury to the myotendinous junction18.
Standard imaging studies of the shoulder may not visualize injuries to the latissimus dorsi, as its attachment could be in the periphery of the chosen field of view. The referral should clearly state clinical suspicion of latissimus dorsi injury to ensure that the correct area is covered. In our case, there were both clinical suspicion and an alert radiographer who added extra slices to the axial series to cover an area of suspected soft-tissue edema. The oblique course of the latissimus dorsi along the thoracic cage makes it often difficult, even with adequate MRI imaging, to visualize a traumatized muscle and tendon19.
In the subsequent follow-up imaging examinations, we attempted to cover more of the muscle belly, but at the price of somewhat reduced image quality.
In the literature, treatment recommendations for LD/TM injuries are predominantly based on younger male baseball pitchers treated non-operatively or surgically.
Erickson and co-workers reported a return to sport rate of 75% amongst 120 baseball pitchers from 2006 to 2011 with a latissimus dorsi / teres major regardless of treatment (non-operative or surgical treatment)20. Interestingly, they found a shorter recovery time to the same competition level in the non-operatively treated pitchers compared to those who underwent surgery, which can be explained by a more extensive injury in those receiving surgical treatment. A grading system based on MRI is proposed by Erickson et al.17:
Grade I: Fluid tracking along latissimus dorsi / teres major Grade II: Partial-thickness tear Grade III: Full-thickness tear, < 2 cm of retraction A: Muscle is torn off the humerus. B: Tear is at the musculotendinous junction. Grade IV: Full-thickness tear, > 2 cm of retraction A: Muscle is torn off the humerus. B: Tear is at the musculotendinous junction
Non-operative management of grade I and II injuries and surgical repair in avulsion injuries in grade III and IV tears were recommended. In the present case report, the injury was an avulsion of both latissimus dorsi and the teres major, and the retraction of the LD tendon was > 2 cm. According to the suggested treatment algorithm by Erickson et al., our patient´s injury may be classified as grade IV-A which implies recommendation for surgical intervention. However, the patient’s choice of non-operative management with self-administered early accelerated functional rehabilitation guided by the gradual reveal of symptoms and limitations led to a full functional recovery with only a negligible cosmetic sequel. The MRI findings of reduced thickness of the muscle fibers on the right side compared to the uninjured left side 38 weeks post-injury suggest that the potential injury-related reduction in strength of the teres major and latissimus dorsi muscles has been compensated by biomechanical adjustments of motion pattern and/or increased contribution from accessory muscles around the shoulder.
The classification system by Erickson et al. does not distinguish between isolated tears to either the LD or the TM, and the conjoined tendon as a whole. The current case demonstrates the need for a clarification of the MRI classification system. A full thickness tear of the LD with a retraction of more than 2 cm may be classified as a severe (grade IV) injury which should be treated surgically according to recommended guidelines17. The successful non-operative treatment of the patient in the current case may be explained by the fact that a small string of the TM tendon remained in contact with its bony attachment on the humerus despite the tear of the rest of the TM and the whole LD with large retractions of more than 2 cm. We propose that tears to the LD and TM tendons are graded as one conjoined tendon tear and that a complete rupture of both the LD and the TM must be present to classify the injury as a grade III or IV according to Erickson et al. As exemplified by the injury in our female middle-aged gymnast, this additional specification would have led to non-operative treatment recommendations similar to the grade II injuries.