The serratus anterior muscle oritinates on the superolateral surfaces of the upper 8 or 9 ribs and inserts into the medial border on the anterior side of the scapula. The serratus anterior muscle is divided into three parts: Serratus Anterior Superior, Serratus Anterior Intermediate, and Serratus Anterior Inferior. The serratus anterior muscle is the most powerful “protractor” of the scapula. The scapula is moved laterally and anteriorly along the chest wall. The serratus anterior muscle is sometimes called the “boxer’s muscle” or the “big swing muscle”. With the same motion that occurs from throwing a punch, the serratus anterior muscle is responsible for pulling of the scapula forward and around the rib cage. The serratus anterior muscle is innervated by the long thoracic nerve. A deficit of the serratus anterior muscle is most commonly caused due to impingement injury of the long thoracic nerve. The long thoracic nerve arises from three nerve roots: the fifth, sixth, and seventh cervical nerves. The long thoracic nerve then passes between the clavicle and first rib, then down along the lateral chest wall giving innervation to the serratus anterior muscle. If the serratus anterior muscle becomes paralyzed, the condition known as “medial winging of the scapula” may occur.
The long thoracic nerve can be injured by trauma, pressure, neuritis/inflammation, and surgery. Signs and symptoms of long thoracic nerve injury include: medial winging of the scapula, difficulty elevating arm, weakness, pain, spasms (periscapular muscles trying to compensate for deformity), and cosmetic deformity. A clinical evaluation test for medial winging of the scapula is referred to as the Wall Test. The patient is asked to face a wall, standing about two feet from the wall and then push against the wall with flat palms at waist level in order to identify a long thoracic nerve injury. During the resistance of forward flexion test, the patient is asked to resist the examiner’s attempt to bring down the forward flexed upper limbs. Lateral scapular winging is different than medial winging of the scapula. Lateral scapular winging is due to dysfunction of the trapezius muscle. Lateral scapular winging involves injury to the spinal accessory nerve.
Nonoperative treatment of medial scapular winging begins is observation for a minimum of 18 months, this is to allow the nerve to recover without surgery. An MRI may be necessary to indicate if a lesion is pressing on the nerve. A muscle test and EMG maybe necessary as well. Serratus anterior strengthening exercises are typically assigned as treatment. Operative treatment consists of a pectoralis major transfer.
