Anatomy of the Long Thoracic Nerve

The long thoracic nerve is a long, thin, and relatively superficial nerve that courses from your cervical spine to the side of your trunk. It supplies motor function to the serratus anterior muscle of your thorax, helping to stabilize your shoulder blade. Injury to this nerve may cause limited or abnormal motion in your shoulder and shoulder blade, including difficulty raising your arm during overhead reaching. The long thoracic nerve is also referred to as the posterior thoracic nerve or the external respiratory nerve of Bell.

Anatomy

The long thoracic nerve arises from the ventral rami of cervical nerves C5, C6, and C7. In some people, the root from C7 is absent, and in others, there is a small root of the nerve arising from C8. The roots from C5 and C6 pierce through the medial scalene muscle to join the C7 nerve root. It then travels behind the brachial plexus and axillary artery and vein as it courses down the lateral side of the thorax. The long thoracic nerve terminates at the lower portion of the serratus anterior muscle, sending small nerve tendrils to each of that muscle's projections where it attaches to the ribs.

Since the long thoracic nerve is superficially located on the lateral side of your chest, it may be subject to injury during sports or surgical procedures. The nerve also has a smaller diameter when compared to other cervical and brachial plexus nerves, increasing its susceptibility to injury.

Function

The long thoracic nerve supplies motor function to the serratus anterior muscle. This muscle attaches to the under-surface of your shoulder blade and inserts as muscular slips to your ribs. When it contracts, it pulls your shoulder blade against your ribs and thorax. The serratus anterior muscle is essential for normal shoulder motion. It helps to move the shoulder blade and stabilizes it during shoulder motions.

Injury to the long thoracic nerve causes a condition called scapular winging. This occurs when the serratus anterior muscle becomes weakened or paralyzed after injury.

Associated Conditions

Since the long thoracic nerve is superficial, it may be easily injured. Injury to the long thoracic nerve may occur as a result of trauma, lifting heavy weights above the shoulder, or a surgical procedure. Surgical procedures that may place the nerve at risk for injury may include:

• Mastectomy
• Thoracotomy
• Improperly placed intercostal drains
• Chest tube placements
• Axillary lymph node dissection

During these surgical procedures, the long thoracic nerve is protected by your surgeon and proper surgical technique, but occasionally difficulties arise during surgery and the nerve may become injured. You may also have an anatomical variance that places your long thoracic nerve in a varied position; your surgeon may not see it and accidentally injure it during surgery.

The superficial long thoracic nerve may also be injured during sports or trauma to the trunk. A blow to the side or a sudden overhead stretch to your shoulder may be enough to damage the nerve, paralyzing the serratus anterior muscle.

Weakness or paralysis of the serratus anterior muscle will result in a winged scapula. To test for this, simply stand about two feet from a wall, facing it. Place both hands on the wall, and gently push against it. If one of your shoulder blades sticks out abnormally, then you may have a winged scapula. (A friend or family member should stand behind you and check your shoulder blade position.) If you suspect winged scapula, a visit to your physician is in order, where he or she can assess your condition and determine if you have a long thoracic nerve injury.

Winging of your scapula may result in difficult lifting your arm overhead. The serratus anterior muscle works with other scapular stabilizers, like the upper trapezius and levator scapula, to properly position your shoulder blade while lifting your arm. Failure of the serratus to stabilize your shoulder blade may make lifting your arm impossible.

Diagnosis of a long thoracic nerve injury typically is made by clinical examination. Plain X-rays and magnetic resonance imaging (MRI) cannot show the nerve injury directly, although an MRI can show some secondary signs to help confirm the diagnosis. An electromyographic (EMG) test may be done to examine the function of the long thoracic nerve.

Rehabilitation

If you have sustained a long thoracic nerve injury, you may benefit from a course of physical therapy to help improve the way your serratus anterior functions. Exercises to improve serratus function may include:

• Supine punches. Lie on your back and raise both arms up towards the ceiling. Make a fist and then punch up towards the ceiling. Make sure your motion is steady and deliberate, and keep your elbow straight. Hold the position for three seconds, and then slowly lower your arm back down to the starting position. Perform 10 to 15 repetitions. Holding a small dumbbell in your hands can make the exercise more challenging.
• Pushup with a plus. Lie on your stomach and place your hands flat on the ground by your shoulders, as if you were going to perform a pushup. Perform a pushup, and then press up further, allowing your shoulder blades to wrap around your thorax. Hold this position for three seconds, and then slowly release. Perform 10 to 15 repetitions. If this is too difficult, you can perform the pushup with a plus against a wall to reduce the effect of gravity on the exercise.

If the long thoracic nerve is severely injured and the serratus anterior is completely paralyzed, then the exercises will not be very effective. In this case, your best course of action is to be as active as possible and to monitor your condition. It may take one to two years for your arm function to recover fully. If permanent nerve injury has occurred, surgery may be an option to restore shoulder motion and function.

There are several different kinds of surgery that can be used to address winged scapula. One involves transferring the pectoralis major tendon to the scapula so it functions as your serratus. Often, the tendon needs to be lengthened, and this may be done by using part of your hamstring tendon. After surgery, you will likely wear a sling on your arm for a few weeks, and then gentle range of motion (ROM) exercises will be initiated. After eight to 10 weeks, gentle progressive strengthening of the new tendon can begin, with full recovery of shoulder motion and strength expected about six to 12 months after surgery.

Understanding the anatomy and function of the long thoracic nerve can help you make informed healthcare decisions after an injury to the nerve.