High-resolution ultrasound and MRI in the evaluation of pectoralis major injuries.

The pectoralis major muscle is the largest muscle of the anterior chest wall. The primary function of the muscle is to adduct and internally rotate the arm at the shoulder. The pectoralis major muscle is broken down into two main components or "heads" based upon muscle fiber origin: clavicular and sternal. Pectoralis major muscle injury results from direct trauma or indirect force overload. The inferior sternal head fibers are the most commonly torn. The pectoralis major tendon most commonly is torn at the humeral insertion. Magnetic resonance imaging and high-resolution ultrasound have value in diagnosing pectoralis major muscle injury and help guide clinical and surgical management. Non-operative versus operative management of pectoralis major tears is dependent upon accurate diagnosis of tear location and severity on imaging. Operative management is recommended for tears at the humeral insertion and for musculotendinous junction tears with severe cosmetic/functional deformity. The indications for surgical intervention have been further expanded to complete intra-tendinous tears, defined as the mid-tendon substance between the myotendinous junction and humeral insertion, and those located at the sternal head/posterior lamina. This paper reviews normal pectoralis major anatomy and the spectrum of injury on magnetic resonance imaging and ultrasound. The importance of regional anatomical landmarks in assessing for pectoralis major muscle injury will be described. Other pathologies, such as tumor and infection, can also affect the pectoralis major muscle and key imaging features will be discussed to help differentiate these entities. Operative and non-operative management of pectoralis major muscle injury is described with examples of pectoralis major repair on post-operative imaging.