Infraspinatus muscle Anatomy

 

Infraspinatus muscle Anatomy

The infraspinatus muscle is one of the four muscles that make up the rotator cuff of the shoulder. It is located on the posterior (back) aspect of the scapula (shoulder blade) and is triangular in shape.

• Origin:
• The infraspinatus muscle originates from the infraspinous fossa, a concave depression on the posterior surface of the scapula below the spine.
• Insertion:
• The muscle fibers of the infraspinatus converge to form a tendon that attaches to the greater tubercle of the humerus (upper arm bone).
• Function:
• The primary function of the infraspinatus muscle is to externally rotate the shoulder joint, which means it helps to turn the upper arm bone away from the body. It also assists in shoulder joint stabilization and in maintaining proper alignment of the humeral head within the glenoid fossa (shoulder socket).
• Innervation:
• The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus.
• Clinical significance:
• The infraspinatus muscle is commonly injured in sports that involve overhead throwing, such as baseball or tennis. It is also frequently involved in rotator cuff tears, which can cause pain and weakness in the shoulder joint. Rehabilitation exercises that target the infraspinatus muscle are often prescribed to help improve shoulder function and reduce the risk of re-injury.

Infraspinatus muscle Anatomy

Origin of Infraspinatus muscle

The infraspinatus muscle originates from the infraspinous fossa, a concave depression on the posterior surface of the scapula (shoulder blade) below the spine. The infraspinous fossa is located on the back of the scapula, just below the spine of the scapula. The muscle fibers of the infraspinatus muscle originate from this fossa and converge to form a tendon that attaches to the greater tubercle of the humerus (upper arm bone). The origin of the infraspinatus muscle is important in understanding its function and the injuries that can affect it.

Insertion of Infraspinatus muscle

The infraspinatus muscle inserts on the greater tubercle of the humerus (upper arm bone). More specifically, the muscle fibers of the infraspinatus converge to form a tendon that attaches to the posterior (back) aspect of the greater tubercle, just inferior to the insertion of the supraspinatus muscle. The insertion of the infraspinatus muscle is important for its function in shoulder joint movement and stability. When the muscle contracts, it pulls on the tendon and causes the humerus to externally rotate (turn the upper arm away from the body) and stabilize within the glenoid fossa (shoulder socket).

Blood Supply

The blood supply to the infraspinatus muscle comes from branches of the suprascapular artery, which arises from the thyrocervical trunk, a branch of the subclavian artery. The suprascapular artery travels along the superior border of the scapula and gives off branches to supply the supraspinatus and infraspinatus muscles, as well as other structures around the scapula. The blood supply to the infraspinatus muscle is important for its nourishment and for maintaining its function. Injuries or disorders that affect the blood supply to the infraspinatus muscle can lead to muscle ischemia (lack of blood flow), muscle weakness, and even muscle death (necrosis).

Nerve Supply

The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus. The suprascapular nerve travels through the suprascapular notch, a bony opening on the superior border of the scapula, and enters the infraspinatus fossa, where it divides into multiple branches that supply the infraspinatus muscle. The nerve fibers that innervate the infraspinatus muscle are primarily motor in nature, meaning they control the muscle's contraction and function. The nerve supply to the infraspinatus muscle is important for its motor function and for maintaining proper shoulder joint movement and stability. Injuries or disorders that affect the suprascapular nerve can lead to muscle weakness, atrophy, and impaired shoulder joint function.

Function of Infraspinatus muscle

The infraspinatus muscle plays an important role in the movement and stability of the shoulder joint. Its primary function is to externally rotate the shoulder joint, which means it helps to turn the upper arm bone away from the body. It also helps to stabilize the humeral head (upper arm bone) within the glenoid fossa (shoulder socket) during shoulder joint movement.

In addition to its primary function of external rotation, the infraspinatus muscle also assists in other shoulder movements, such as shoulder extension (pulling the arm back), horizontal abduction (moving the arm away from the midline of the body), and scapular stabilization (holding the shoulder blade in place). The muscle works in conjunction with the other muscles of the rotator cuff, as well as the larger muscles of the shoulder and upper back, to provide optimal shoulder joint function and movement.

Injuries or disorders that affect the infraspinatus muscle can lead to weakness, pain, and impaired shoulder function. Rehabilitation exercises that target the infraspinatus muscle are often prescribed to help improve shoulder function and reduce the risk of re-injury.

Exercise of Infraspinatus muscle

Strengthening the infraspinatus muscle can be beneficial for improving shoulder joint function, stability, and reducing the risk of injury. Here are some exercises that can target the infraspinatus muscle:

External Rotation with Dumbbell: This exercise targets the infraspinatus muscle specifically. To perform this exercise, sit on a bench with your elbow bent to 90 degrees and your upper arm against your side. Hold a dumbbell in your hand with your palm facing inwards. Slowly rotate your arm outward, away from your body, until your forearm is parallel to the ground. Pause for a moment, then slowly return to the starting position.

Face Pulls: This exercise targets the infraspinatus as well as other muscles of the upper back. To perform this exercise, attach a resistance band to a stable object at chest height. Hold the ends of the band with your palms facing inward and your arms extended in front of you. Pull the band towards your face, leading with your elbows. Pause for a moment, then slowly return to the starting position.

Scapular Retraction: This exercise targets the muscles of the upper back, including the infraspinatus. To perform this exercise, stand or sit with your arms at your sides and your shoulders relaxed. Squeeze your shoulder blades together and hold for a few seconds, then release.

Prone Shoulder Extension: This exercise targets the infraspinatus, as well as the other muscles of the rotator cuff. To perform this exercise, lie face down on a bench or exercise ball with your arms at your sides. Slowly lift your arms off the ground, squeezing your shoulder blades together and leading with your elbows. Pause for a moment, then slowly lower your arms back down.

It's important to consult with a healthcare professional or a certified personal trainer before beginning any new exercise program to ensure proper form and technique, and to avoid injury.

Stretch of Infraspinatus muscle

Stretching the infraspinatus muscle can help improve its flexibility and reduce the risk of injury. Here's a stretch that can target the infraspinatus muscle:

Cross-Body Shoulder Stretch: This stretch targets the infraspinatus muscle as well as the other muscles of the rotator cuff. To perform this stretch, stand with your feet shoulder-width apart and your arms at your sides. Bring your right arm across your chest and hold it with your left hand at the elbow. Gently pull your right arm towards your left shoulder until you feel a stretch in your right shoulder. Hold the stretch for 20-30 seconds, then release and repeat on the other side.

It's important to perform stretches slowly and gently, and to avoid overstretching or forcing the muscle beyond its natural range of motion. If you have any pain or discomfort during stretching, stop the exercise and consult with a healthcare professional.

Strengthening Exercise off Infraspinatus muscle

Strengthening the infraspinatus muscle can help improve shoulder joint function and stability, reduce the risk of injury, and enhance sports performance. Here are some strengthening exercises that can target the infraspinatus muscle:

External Rotations with Resistance Band: Attach a resistance band to a stationary object at elbow height. Stand facing the object with your elbow bent at a 90-degree angle and your forearm parallel to the ground. Grab the band with the hand of the arm you want to strengthen and rotate your arm away from your body against the resistance of the band. Slowly return your arm to the starting position and repeat for several repetitions. Then switch arms and perform the exercise with your other arm.

Dumbbell Reverse Fly: Stand with your feet shoulder-width apart and hold a dumbbell in each hand with your palms facing inward. Lean forward slightly, bending your knees slightly, and then raise both arms straight out to your sides. Keep your arms straight and lift the dumbbells to the level of your shoulders. Pause for a moment, then slowly lower the weights back to the starting position.

Scapular Retraction: Stand with your arms at your sides, palms facing your thighs. Squeeze your shoulder blades together, pulling them towards your spine. Hold the squeeze for a few seconds, then relax and repeat for several repetitions.

Prone Shoulder Extension with External Rotation: Lie face down on a bench or stability ball with your arms at your sides, palms facing down. Lift both arms off the ground while keeping them straight, and then rotate them outward, away from your body. Hold the position for a moment, then slowly lower your arms back to the starting position.

It's important to consult with a healthcare professional or a certified personal trainer before beginning any new exercise program to ensure proper form and technique, and to avoid injury.

Clinical Significance

The infraspinatus muscle has clinical significance in the following ways:

Rotator Cuff Injury: The infraspinatus muscle is one of the four muscles that make up the rotator cuff, which is a group of muscles and tendons that help stabilize the shoulder joint. Injury to the rotator cuff, including the infraspinatus muscle, can cause pain, weakness, and limited range of motion in the shoulder joint.

Shoulder Impingement Syndrome: Infraspinatus muscle weakness can contribute to shoulder impingement syndrome, a condition in which the tendons of the rotator cuff become compressed and irritated as they pass through the shoulder joint. This can cause pain, weakness, and limited range of motion in the shoulder joint.

Shoulder Dislocation: The infraspinatus muscle plays a role in stabilizing the shoulder joint, and weakness or injury to the muscle can increase the risk of shoulder dislocation.

Tennis and Pitcher's Shoulder: Infraspinatus muscle strain or injury is common in athletes who use repetitive overhead motions, such as tennis players and baseball pitchers. This can cause pain, weakness, and limited range of motion in the shoulder joint.

Assessment of Shoulder Function: Evaluation of the infraspinatus muscle strength and function is an important component of a comprehensive shoulder assessment, particularly in patients with shoulder pain, weakness, or limited range of motion.

In summary, the infraspinatus muscle plays an important role in shoulder joint function and stability, and injury or weakness of the muscle can lead to various clinical conditions affecting the shoulder joint.