The diagnostic performance of MRI signs to distinguish Pectoralis major tendon avulsions from Myotendinous injuries.

Background: Management of pectoralis major (PM) injuries is largely determined by the anatomic location of the injury, with tendon avulsions from the humerus requiring surgery while myotendinous (MT) injuries are typically managed non-operatively. Because physical examination cannot reliably make this distinction, MRI is often used for staging. However, correct classification can also be difficult with MRI where there is extensive soft tissue edema and distorted anatomy.

Objective: To determine the diagnostic performance of primary and secondary MRI signs of PM injury for distinguishing tendon avulsions from MT injuries in a selected sample of patients that underwent surgical repair using a practical interpretation algorithm.

Methods: In this retrospective study, 3 blinded observers independently assessed the MRI findings of 17 patients with PM injury (including 12 acute injuries, 4 chronic, and 1 of uncertain age) where subsequent surgery documented tendon avulsion (11) and MT injuries (6) by applying the primary MRI criteria of absent tendon at the humerus, retracted tendon stump, epicenter of edema, and the secondary finding of soft tissue edema contacting the anterior humeral cortex. Operative findings were used as the reference standard. Sensitivity, specificity, and positive and negative predictive value were recorded for each finding.

Results: The primary MRI finding of lack of a visible tendon at the insertion (sensitivity 82-100%, specificity 100%) and the secondary finding of edema contacting the anterior humeral cortex (sensitivity 64-91%, specificity 67-100%) were both useful for the distinction of tendon avulsion from MT injury, particularly in acute injuries. The presence of a retracted tendon stump and the epicenter of edema were not reliable findings. The use of a decision tree including the secondary finding of humeral edema increased the sensitivity and specificity for 2 of the 3 observers.

Conclusion: MRI assessment of PM injury focused on the humeral insertion of the PM tendon allows accurate distinction of tendon avulsion from MT injury.

Clinical Impact: This study describes a practical approach to classifying PM injuries with MRI to distinguish injuries that require surgery from those that can potentially be managed conservatively.