The Anatomy of the Ulna

The Bone That Breaks in a Wrist Fracture

In This Article

The ulna, along with the larger and stronger radius, makes up the forearm. Being longer and thinner, the ulna is often more easily fractured as a result of trauma. The upper end (the head) of the ulna meets with the lower end of the humerus and one side of the radius. The size and location of the ulna allow for more freedom of movement and increased rotation of the forearm.

This placement of the ulna in relation to the radius allows for humans to have more range of motion in the forearm as compared to other mammals.

Anatomy

The top end of the ulna has a distinguishing feature which sets it apart from other bones, including the similar radius. The top of the ulna forms a C-shaped bump, which is made up of both the radial notch and the trochlear notch. As its name suggests, the radial notch is the point where the radius joins the ulna. These two structures rest on each other and combine to form the forearm. This notch allows for the radius to move smoothly and freely on the ulna, which allows for the rotation of the forearm.

The trochlear notch is the area on which the humerus joins the ulna. This union occurs near the elbow joint, where the humerus from the top portion of the arm ends and the ulna from the lower portion of the arm begins.

The meeting and movement between the humerus and the ulna allow the common motion of bending and straightening the arm at the elbow to occur.

As with nearly any part of the body, a deformity can occur. Madelung’s deformity is a birth defect resulting in the poor formation of the palmar ligament and the forearm bones. This causes chronic or persistent dislocation of the ulna, along with a shortened forearm. This is just one of the diagnoses affecting the ulna which can be addressed surgically and therapeutically.

Function

The main function of the ulna, along with the radius, is to assist with rotation. This rotation allows for maximal function of the wrist and hand due to the increased range of motion. The sole motion of the elbow joint is flexion and extension, otherwise known as bending and straightening the arm. Due to this limitation, the forearm allows for increased motion of the wrist and hand without warranting any motion from the elbow joint.

The configuration of the ulna on the radius allows for the lower portion of the forearm to give motion to the wrist and the hand. This allows for precise functions such as writing, manipulating buttons or other small objects, turning doorknobs, carrying objects, using tools, typing, and more. Such motions tend to require the use of the wrist and individual fingers, which requires a stable upper arm along with rotation and mobility of the forearm.

Associated Conditions

A diaphyseal forearm fracture, commonly known as a wrist fracture, is one of the most common injuries to the ulna. Though this fracture can occur as the result of a multitude of trauma-related reasons, the leading cause is falling on an outstretched arm. For this reason, a diaphyseal forearm fracture usually happens in a younger population, as their reflexes cause them to attempt to break their fall.

Fracture to both forearm bones, the ulna, and the radius is typically the result of a fall or other related incident.

A single fracture to the ulna (or radius) is usually seen in instances where a direct blow or outside force acts on the bone.

Types of fractures that can affect the ulna include:

  • Greenstick Fractures: These are partial fractures, also known as hairline fractures to an otherwise intact bone.
  • Complete Fractures: These are full fractures where the bone breaks into two pieces.
  • Compound Fractures: Also known as open fractures, this occurs when a piece of bone fragment pierces the skin.
  • Closed Fractures: This is a partial or full fracture where the bone does not pierce the skin.
  • Comminuted Fractures: This occurs when the bone breaks into multiple smaller pieces.

Another type of fracture that differs from the others is a stress fracture. Stress fractures are not the result of a single traumatic event, as they occur slowly over time due to inappropriate positioning or repetitive overuse. Treatment for stress fractures varies based on the type of fracture which results; however, they are still considered urgent in nature to prevent further deformity.

Individuals who receive stress fractures should be educated on prevention of future stress fractures as part of their rehabilitation course.

Treatment of a closed fracture is typically less complicated than the treatment of an open fracture due to a decreased risk of infection. However, both treatments are urgently needed after a fracture of any kind to prevent bone and joint deformity and decrease the risk for impaired function.

Rehabilitation

Therapeutic rehabilitation and medical treatments will vary based on the type of fracture. Medical treatment is generally divided into two categories: open reduction with internal fixation (ORIF) and closed reduction.

Open Reduction

Open reduction with internal fixation is how doctors will treat bones that have broken into two or more pieces, along with bones that have pierced the skin. This involves an open reduction, meaning doctors must make an incision to access the bones, along with an internal fixation, which is any type of hardware including plates, screws, rods, and nails which secure the bone back in its original place.

This hardware is usually removed once the doctor determines the patient is adequately healed. This procedure is followed by placing the patient in a soft cast or splint for protection while the patient slowly resumes some daily activities.

Closed Reduction

Closed reduction is completed in-office by the doctor who uses manual techniques (use of only his hands) to reset the bone. This will be followed by placement of a hard cast to protect the arm and prevent re-injury while the patient slowly resumes some daily activities.

Healing rates differ depending on a person’s other conditions, age, and the type of fracture, however, doctors typically follow a recovery protocol specific to the bone and the type of fracture. Doctors typically require a patient to not bear weight on the forearm for the first two weeks after a fracture; sutures or staples are typically also removed after this second week.

Depending on the healing process and the patient’s progress, doctors typically allow a five-pound weight limit after the second week with the restriction to not complete any forearm rotation. Rotational motion, if completed too early, can cause re-injury. Once the doctor confirms the bones are healed after taking imaging (X-rays), these weight restrictions will typically be lifted. This usually occurs around six weeks after surgery.

Therapy

Therapeutic rehabilitation can be provided by a physical therapist or an occupational therapist in an outpatient clinic setting. Treatment from a rehabilitation professional is indicated after removal of fracture hardware and after any fracture to the arm, wrist, or hand. Therapists can also assist in educating patients on how to prevent future fractures with exercises and techniques.

Therapy programs will typically include exercises to improve coordination, strengthening, and range of motion of the forearm, education on equipment use to compensate for some temporary loss of function during the healing process, and practice of daily activities which may be more difficult due to the injury and/or surgery.

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Article Sources
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