Aponeurosis

What is aponeurosis?

An aponeurosis is a flat sheet of connective tissue in your body that’s important for movement and posture. Aponeuroses (plural) are similar to your tendons, but they have a slightly different role. They cover your muscles and act as insertion points for your muscle fibers to connect your muscles to your bones and cartilage.

How is an aponeurosis functionally similar to a tendon?

The aponeurosis function is similar to a tendon. They both attach your muscles to your bones. When you move one of your muscles by flexing or extending it, an aponeurosis functions as a spring to endure the tension and extra pressure. It absorbs energy when your muscles move.

In contrast, your tendons stretch and contract during those muscle movements. When you contract a muscle, your tendon moves a bone. Tendons allow your body to move and give you flexibility. Aponeuroses give your body strength and stability.

In addition, aponeuroses can act like another type of connective tissue called fascia. Fascia is fibrous tissue that wraps around and supports your muscles, organs and bones.

How does an aponeurosis differ from a tendon structurally?

Aponeuroses and tendons are both made of dense, fibrous connective tissue, but they look very different.

An aponeurosis is a delicate, thin sheet of tissue that contains collagen-releasing cells called fibroblasts. It contains bundles of collagen fibers organized in a parallel pattern, which keeps it strong. You rarely injure your aponeuroses because they’re hidden under many layers of bone and muscle.

Tendons are rough, thick structures that extend from your muscles. They look like rounded cords or ropes. Although they’re tougher, you can injure them more easily because they’re not hidden away under your bones and muscles.

What are some aponeurosis examples?

You have many different aponeuroses in your body. Some examples include:

Bicipital aponeurosis

Your bicipital aponeurosis is a wide sheet of tissue in your biceps. Your biceps are arm muscles on the front part of your upper arms. Your bicipital aponeurosis is located near the inner part of your elbow. It strengthens this area and helps protect your brachial artery and median nerve, both found within your upper arm.

Epicranial aponeurosis

Your epicranial aponeurosis extends over the upper part of your skull. It’s like a thin helmet beneath your scalp, which has three layers. Your skin makes up the outermost first layer. Dense connective tissue makes up the second layer. Your epicranial aponeurosis forms the third layer. All three layers move together to help support a muscle in your skull that controls your facial expressions.

Palmar aponeurosis

Your palmar aponeurosis is located in the palm of your hand. It stretches from the crease of your wrist to the base of your fingers. It attaches to the skin in the palm of your hand, allowing you to cup and grip objects. It also protects your tendons and muscles. Over time, the shortening and thickening of your palmar aponeurosis can cause a condition called Dupuytren’s disease.

Plantar aponeurosis

Your plantar aponeurosis, or plantar fascia, is located in the sole of your foot. It stretches from your heel bone to the front part of your foot. Your plantar aponeurosis protects the nerves and vessels in your foot. It supports the arch of your foot and helps control movement around your ankle. It also distributes force evenly across your foot. If you overstretch your plantar aponeurosis, it may lead to plantar fasciitis.

Erector spinae aponeurosis

Your erector spinae aponeurosis (ESA) is located in your lower back. It blends with your thoracolumbar fascia (TLF). Your TLF is another dense connective tissue that surrounds your back muscles. Together, your ESA and TLF separate your spinal muscles from the muscles in your abdominal wall. They’re important for breathing, posture and load transfer.

Aponeurosis of the external oblique

The aponeurosis of your external oblique attaches to your outer abdominal oblique muscle. This muscle extends from the lower half of your ribs down the sides of your body to your pelvis. The aponeurosis of your external oblique helps your oblique muscles twist your trunk from side to side. It also helps with the movement of your spine.

A note from Cleveland Clinic

Aponeuroses are flat sheets of connective tissue in your body that are similar to tendons. They cover your muscles and help connect your muscles to your bones and cartilage. You have aponeuroses all over your body. They provide support for your muscles and they give your body strength and stability. You need aponeuroses to help your body move.