The Anatomy of the Serratus Anterior Muscle

The muscle that attaches your shoulder blade to the rib cage

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The serratus anterior is a muscle that attaches your shoulder blade, known as your scapula, to your rib cage. The muscle helps to move your scapula in various directions and is essential for proper shoulder function. Injury to the serratus anterior is rare, but if it happens, you may require rehabilitation to get your shoulder moving and functioning normally again.

Anatomy

The serratus anterior originates via eight muscular "slips" that attach to the side of your ribs. It then courses around the side of your rib cage and underneath your scapula. There, it inserts along the medial border of your scapula.

This muscle lies between the back of your rib cage and your shoulder blade near the subscapularis (one of the four rotator cuff muscles). A small fluid-filled sac called a bursa lies between the subscapularis and serratus anterior that allows the scapula to glide and slide normally during movement.

There are three divisions of the serratus anterior. These are:

  • The serratus anterior superior
  • The serratus anterior intermediate
  • The serratus anterior inferior

Each of the divisions of the muscle function together to move your scapula in various directions.

The serratus anterior is innervated by the long thoracic nerve. This nerve originates from the brachial plexus, a bundle of nerves that emerge from your cervical spine and course down your shoulders and arms.

You have two serratus anterior muscles; there is one on each side of your body.

Function

The serratus anterior muscle protracts the shoulder blades. This means that they pull them forward around your rib cage. Think of a boxer throwing a punch; as his arm comes forward, the serratus anterior contracts to pull the shoulder blade around the ribs and forward.

The inferior and superior aspect of the serratus also helps to stabilize your shoulder blade against your rib cage. When they contract together, they work with the rhomboid muscles to pull your scapula tight against the back of your ribs.

When your arm and shoulder are in a fixed and stable position, the serratus anterior helps to elevate your ribs. This occurs during normal breathing. Thus, the serratus anterior muscles are considered secondary muscles of respiration.

Associated Conditions

Injury to the serratus can result in a condition called a winged scapula. This manifests as a visual bump in your back where your shoulder blade resides.

One common cause of a serratus anterior injury is a problem with the long thoracic nerve. This nerve resides near your armpit, and it may be damaged during surgical procedures involving your shoulder.

Injury to the long thoracic nerve may occur during lymph node resection in patients with breast cancer. The nerve can also be overstretched during athletic activity.

Since the serratus anterior attaches to the side of your rib cage, an injury to your ribs may also cause damage to the muscle. A rib fracture can cause the muscle tissue of the serratus to pull away, resulting in an avulsion fracture. This can be a painful injury and limit function of the serratus anterior.

Sometimes, serratus anterior weakness and winging of the scapula can occur for no apparent reason. A condition known as Parsonage-Turner Syndrome may affect your brachial plexus and the long thoracic nerve. This brachial neuritis may cause weakness in your serratus and manifest as the telltale scapular winging.

An injury to your shoulder or rotator cuff may also cause scapular winging. Conditions like rotator cuff tear or a shoulder separation may cause pain and inhibition of the muscles that support your shoulder. If the serratus anterior becomes inhibited, it may fail to adequately hold your shoulder blade to your ribs, leading to scapular winging.

Testing the Serratus Anterior

The "serratus wall test" is often performed to assess the function of the serratus anterior. To do this test:

  • Stand about two feet from a wall, facing it.
  • Place both hands on the wall with your shoulders elevated to about 90 degrees.
  • Perform a pushup.

Have someone watch the position of your shoulder blades. If one shoulder blade wings out, there may be weakness in your serratus anterior on that side.

If you suspect you have an injury to your serratus or find that your shoulder blade is winging, you should visit your physician for a full assessment. Your doctor can determine the cause of your problem and refer you to the right professional to help regain function of your serratus muscle.

Rehabilitation

An injury to your serratus anterior may cause scapular winging, shoulder motion limitations, and difficulty with normal upper extremity function. Working with a physical therapist can help you recover after an injury to your serratus.

Treatments that you may encounter during rehab for your serratus anterior may include:

These treatments are designed to improve the way your shoulder moves and functions.

Exercises that may be done to improve the strength and function of your serratus anterior may include:

  • Supine punches: Lie on your back with your arm raised up towards the ceiling. Make a fist, and then slowly punch up towards the ceiling. Hold the position for three seconds, and then slowly lower your arm back down. Your elbow should remain straight during this exercise. Be sure to move with slow and steady motions and feel your shoulder blade wrapping forward around your rib cage during the movement. To make the exercise more challenging, you can hold a small dumbbell. Perform 10 to 15 repetitions.
  • Pushups with a plus: Lie on your stomach with your hands flat on the floor underneath your shoulders, as if you were going to start a pushup. Perform a pushup, and then press up further, allowing your shoulder blades to wrap forward around your rib cage. You should feel your middle spine move up towards the ceiling as your scapulae protract. Hold this position for three seconds, and then return to the starting position. Repeat ten repetitions. (If performing the pushup with a plus is too challenging, you can try it against a wall.)
  • Serratus wall slide: Stand facing a wall, and place both elbows and forearms against the wall. Your arms should be in front of you, slightly in a "V" shape. Slowly slide your forearms up the wall, allowing your shoulder blades to protract forward as you slide up. Hold this position for three seconds, and then slowly return to the starting position. Repeat 10 to 15 times.

Be sure to check with your physician before starting this, or any other, exercise program for your shoulders or serratus anterior. If any exercise causes pain, stop and visit your physician.

A Word From Verywell

Your serratus anterior is a major scapular stabilizer that essentially holds your shoulder blades to your rib cage. An injury here can cause pain, limited motion, scapular winging, and difficulty using your arm normally. Understanding the anatomy and function of your serratus anterior can help you properly rehab it after an injury.

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