Muscle Insertion and Your Joints

A muscle attaches at either the muscle origin or the muscle insertion. The insertion of a muscle is defined as the place where one end of a muscle is attached to the freely moving bone of its joint.

This article discusses muscle insertions and joints. It explains how muscles attach to bones and support joints and common problems that may affect muscle insertions.

How Muscles Attach to Bone

A muscle is a group of tightly bundled elastic fibers wrapped in thin connective tissue. Muscles attach to bones via tendons made from strong, flexible connective tissue. 

Muscles attach to bone on either end of a joint and contract to produce joint movement. Each muscle has at least two connection points:

• Origin: This point is attached to the bone that remains stable and does not move with muscle contraction. Muscle origins are usually closer to the center of the body (proximal).
• Insertion: This point is attached to the bone that moves in the joint. Muscle insertions are typically on the bone farther away from the center of the body (distal).

Muscle names often refer to their insertion point. For example, the rectus femoris is a big, bulky muscle that runs from the pelvis down the front of your thigh bone (femur).

Insertion Points Move Joints

Joint movement occurs as one bone acts freely while the other remains stationary. Muscle contractions near the muscle origin draw the bone of the insertion point closer to move the joint.

The muscle insertion is typically on the bone farthest from the center of the body, but the points can switch roles depending on the action and position.

For example, hip flexion moves the leg when walking, but the pelvis performs the movement when bending forward.

Types of Insertion Injuries

Muscle insertion sites can experience overuse injuries and other traumas known as tendinopathies. These include:

• Tendonitis: Inflammation of a tendon
• Tenosynovitis: Inflammation of a tendon and the protective covering around it (tendon sheath)
• Torn tendon: A partial or complete tear of the connective tissue

Tendon Tears

A tendon tear is typically caused by an acute, sudden movement and may cause a pop or snapping sensation at the moment of injury. The result is pain, joint swelling, and difficulty moving the joint or bearing weight on the affected limb—for example, a torn Achilles tendon.

A partial tendon tear may heal with rest, ice, and physical therapy. A complete tear often requires surgery.

Tendonitis and Tenosynovitis

Tendonitis and other tendinopathies can be caused by repetitive movements, excessive joint loading, muscle imbalances, or abnormal tendon loading from misaligned joints. Aging, compression, dehydration, and awkward postures can also contribute to inflammation and pain at tendon insertion sites.

These tendon injuries often resolve with rest, ice, and physical therapy. Tendinopathies are often named for the sport they are associated with. However, other repetitive motions can cause them as well. Common tendinopathies include:

• Lateral epicondylitis, better known as tennis elbow, causes pain on the outside of the elbow. 
• Medial epicondylitis, or golfer's elbow, causes pain on the inside of the elbow.
• Patellar tendinopathy, or jumper's knee, causes pain in the front of the knee, particularly during activities that involve jumping and running.
• Rotator cuff tendinopathy causes pain and weakness in the tendons and muscles in the shoulder.

In some people, tendon problems are caused by an abnormal extracellular matrix (ECM) composition, which impairs tissue healing. This is more common in people with genetic connective tissue disorders, such as Ehlers-Danlos and Marfan syndromes.

Tenosynovitis can also be caused by an infection or inflammatory disease, such as rheumatoid arthritis and lupus. Treating the underlying cause can help to relieve symptoms.

Examples of Muscle Insertions

The following examples provide a closer look at how muscle insertions and origins work together to move different joints.

Sternocleidomastoid Muscle (SCM)

One prominent muscle in the neck is the sternocleidomastoid (SCM). The main job of the SCM is to turn and tilt your head, and it also assists when you bend your head forward or extend it backward. 

This muscle runs from the breastbone/collarbone (origin) to the mastoid process (insertion). The mastoid process is a little projection of bone located behind your ear. To feel the mastoid process, you can touch that tag of bone behind your ear with your finger.

The origin of the SCM actually divides into two parts, with each attaching to different, but nearby areas.

Each section of the origin is described as a head. One head of the SCM originates on the top of the collarbone, close to the center of your body. The other head originates at the outside surface of the top of your breastbone.

Latissimus Dorsi Muscle (Lats)

The latissimus dorsi muscle is a very large back muscle that starts mainly from the area around your hips and back and goes all the way to your upper extremity. This large muscle originates at the pelvis, ribs, thoracolumbar fascia, and some vertebrae.

Despite its size, the latissimus dorsi muscle eventually tapers to an insertion point that is located on the inside of your humerus. The humerus is the upper arm bone.

Summary

Muscle insertion is the point where a muscle attaches to the moveable bone in the joint. This is usually the part of the joint further from the center of the body.

Muscles typically originate at the body part closest to the trunk, known as the origin. The muscle crosses the joint and attaches to the insertion point via tendons. When the muscle contracts, the bone of the insertion point moves.

Muscle insertions can be injured due to trauma, overuse, repetitive stress, aging, and genetic conditions. Tendonitis, tenosynovitis, and tendon tears are common soft-tissue injuries that affect muscle insertion sites.

Tendon injuries can be painful and restrict joint movement. They often resolve with rest, ice, physical therapy, and treatment of the underlying cause. In some cases, surgery may be required.