The Role of the Long Thoracic Nerve in Shoulder Stability

Can understanding the anatomy and function of the long thoracic nerve help individuals make informed healthcare decisions after an injury to the nerve?

Long Thoracic Nerve

Also referred to as the posterior thoracic nerve, the long thoracic nerve/LTN is a thin superficial nerve that runs from the cervical spine to the chest wall side of the trunk. It supplies motor function to the thorax’s serratus anterior muscle, helping stabilize the shoulder blade. Injury to this nerve can cause limited or abnormal shoulder and shoulder blade motion, including difficulty raising the arm during overhead reaching.

Anatomy

The long thoracic nerve originates from the ventral rami of cervical nerves C5, C6, and C7. (Waxenbaum JA, Reddy V, Bordoni B. 2023) In some individuals, the root from C7 is absent; in others, a small nerve root branches from C8. The nerve roots from C5 and C6 go through the medial scalene muscle to join the C7 nerve. It travels behind the brachial plexus axillary artery and vein and 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 muscle’s projections, which attach to the ribs. Because the long thoracic nerve is located on the lateral side of the chest, it is vulnerable to injury during sports or surgical procedures. The nerve also has a smaller diameter than other cervical and brachial plexus nerves, which increases its potential for injury.

Function

The long thoracic nerve attaches to the underside of the shoulder blade and inserts as muscular slips into the ribs. It supplies motor function to the serratus anterior muscle, essential for normal shoulder motion. When it contracts, it pulls the shoulder blade against the ribs and thorax, helping to move and stabilize the arm as it moves forward and up 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. (Lung K, St Lucia K, Lui F. 2024)

Susceptibility to Injury

The LTN is relatively unprotected and can be damaged by several things, including:

• Heavy backpacks
• Sports
• Activities the body is not used to, like digging
• Using crutches

Conditions

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: (Lung K, St Lucia K, Lui F. 2024)

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

The long thoracic nerve is protected during these procedures by the surgeon and proper surgical technique, but occasionally, difficulties arise during surgery, and the nerve may become injured. Individuals may also have an anatomical variance that places their nerves in varying positions. The surgeon may not see it and accidentally injure their nerves 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 the 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:

• Stand about two feet from a wall, facing it.
• Place both hands on the wall and gently push against it.
• If one of the shoulder blades sticks out abnormally, it could be a winged scapula.
• Have a family member or friend stand behind you and check the shoulder blade position.
• If you suspect a winged scapula, visit a physician who can assess the condition and determine if there is a long thoracic nerve injury.

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

Clinical examination is usually used to diagnose a long thoracic nerve injury. X-rays and MRIs cannot show the nerve injury directly, although an MRI can show some secondary signs to help confirm the diagnosis. An electromyographic or EMG test may also be performed to examine the function of the long thoracic nerve.

Treatment and Rehabilitation

Treatment for LTN pain and reduced movement may include:

• Rest
• Heat or ice
• Anti-inflammatory pain medication
• Neck support or a pillow
• Avoiding strenuous activity and driving

If the long thoracic nerve is severely injured and the serratus anterior is completely paralyzed, the best course of action is to be active and monitor the condition. Full recovery of arm function can take one to two years. If permanent nerve injury has occurred, surgery may be an option to restore shoulder motion and function. Several different kinds of surgery can be used to address winged scapula. (Vetter M. et al., 2017)

• One involves transferring the pectoralis major tendon to the scapula (Vetter M. et al., 2017) so it functions as the serratus.
• Often, the tendon has to be lengthened, which may be done using part of the hamstring tendon.
• After surgery, individuals will likely wear a sling on their arm for a few weeks, and then gentle range-of-motion exercises will be initiated.
• After eight to ten weeks, gentle progressive strengthening of the new tendon can begin.
• Full shoulder motion and strength recovery are expected six to 12 months after surgery.

Physical therapy may be used to help improve serratus anterior functions. (Berthold J. B., Burg T. M., & Nussbaum R. P. 2017) Exercises to strengthen serratus function may include:

Supine Punches

• Lie on your back and raise both arms toward the ceiling.
• Make a fist and punch up toward the ceiling.
• Ensure the motion is steady and deliberate, and keep the elbow straight.
• Hold the position for three seconds, then slowly lower the arm to the starting position.
• Perform 10 to 15 repetitions.
• Holding a small dumbbell in your hands can make the exercise more challenging.

Pushup

• 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 press further, allowing the shoulder blades to wrap around the thorax.
• Hold this position for three seconds, and slowly release.
• Perform 10 to 15 reps.
• If this is too difficult, perform the pushup against a wall to reduce the effect of gravity on the exercise.

Scapular Winging in Depth

References

Waxenbaum, J. A., Reddy, V., & Bordoni, B. (2024). Anatomy, Head and Neck: Cervical Nerves. In StatPearls. https://www.ncbi.nlm.nih.gov/pubmed/30844163

Lung, K., St Lucia, K., & Lui, F. (2024). Anatomy, Thorax, Serratus Anterior Muscles. In StatPearls. https://www.ncbi.nlm.nih.gov/pubmed/30285352

Vetter, M., Charran, O., Yilmaz, E., Edwards, B., Muhleman, M. A., Oskouian, R. J., Tubbs, R. S., & Loukas, M. (2017). Winged Scapula: A Comprehensive Review of Surgical Treatment. Cureus, 9(12), e1923. https://doi.org/10.7759/cureus.1923

Berthold, J. B., Burg, T. M., & Nussbaum, R. P. (2017). Long Thoracic Nerve Injury Caused by Overhead Weight Lifting Leading to Scapular Dyskinesis and Medial Scapular Winging. The Journal of the American Osteopathic Association, 117(2), 133–137. https://doi.org/10.7556/jaoa.2017.025