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Acetabular Fractures

Acetabular Fractures

An acetabular fracture is a break in the socket portion of the “ball-and-socket” hip joint. These hip socket fractures are not common — they occur much less frequently than fractures of the upper femur or femoral head (the “ball” portion of the joint).

The majority of acetabular fractures are caused by some type of high-energy event, such as a car collision. Many times patients will have additional injuries that require immediate treatment.

In a smaller number of cases, a low-energy incident, such as a fall from standing, may cause an acetabular fracture in an older person who has weaker bones.

Treatment for acetabular fractures often involves surgery to restore the normal anatomy of the hip and stabilize the hip joint.

Anatomy

The hip is one of the body’s largest joints. It is a “ball-and-socket” joint. The socket is formed by the acetabulum, which is part of the pelvis. The ball is the femoral head, which is the upper end of the femur (thighbone).

 
Normal hip anatomy

The acetabulum is the “socket” of the “ball-and-socket” hip joint.

 
Normal hip anatomy, side view

 

In a healthy hip, the ball fits securely inside the socket and rotates easily within the smooth cartilage lining.

The bone surfaces of the ball and socket are covered with articular cartilage—a smooth, slippery substance that protects and cushions the bones and enables them to move easily.

Bands of tissue called ligaments connect one bone to another. These ligaments help provide both function and stability to the hip joint, allowing it to move without falling out of the socket.

Major nerves, blood vessels, and portions of the bowel, bladder, and the reproductive organs all pass within or close to the pelvis. These structures can occasionally be damaged as the result of an injury to the acetabulum.

 
The ligaments, muscles, and nerves of the pelvis and hip joint
The ligaments, muscles, and nerves surrounding the pelvis and hip joint. On the right side of this drawing, anatomy layers are “cut away” to more clearly show all structures.
Reproduced with permission from JF Sarwark, ed: Essentials of Musculoskeletal Care, ed 5. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2016.

Description

Acetabular fractures vary. For example, the bone can break straight across the socket or shatter into many pieces. When the acetabulum is fractured, the femoral head may no longer fit firmly into the socket, and the cartilage surface of both bones may be damaged.

If the joint remains irregular or unstable, ongoing cartilage damage to the surfaces may lead to arthritis.

Severity

The severity of the injury depends on several factors, including:

  • The number and size of the fracture fragments
  • The amount each piece is out of place (displaced) — In some cases, the broken ends of bones line up adequately; in more severe fractures, there may be a large gap between the broken pieces, or the fragments may overlap each other.
  • The injury to the cartilage surfaces of both the acetabulum and the head of the femur
  • The injury to surrounding soft tissues, such as muscle, tendons, nerves, and skin

If the bone breaks in such a way that bone fragments stick out through the skin or a wound penetrates down to the broken bone, the fracture is called an “open” or compound fracture. This type of fracture is particularly serious because, once the skin is broken, infection in both the wound and the bone can occur. Immediate treatment is required to prevent infection.

Open fractures of the acetabulum are rare because the hip joint is well covered with soft tissues. When they do occur, they are usually the result of very high-energy trauma.

Pattern of Injury

The anatomy of the pelvis provides bony support for both the front (anterior) and back (posterior) of the hip socket. Doctors have identified a number of different acetabular fracture patterns. These fracture patterns are based on:

  • Location–such as a break in the anterior (front) or posterior (back) column of the bone or the area around the bony rim (wall) of the acetabulum
  • Orientation–such as a break that is straight across the bone

Acetabular fractures can also occur in a combination of patterns. Knowing the severity and specific pattern of your fracture will help your doctor determine treatment.

 
The anterior (front) and posterior (back) columns of the acetabulum.

The anterior (front) and posterior (back) columns of the acetabulum.

Common acetabular fracture patterns include:

 
Anterior wall and anterior column acetabulum fractures

(Left) Anterior wall fracture
(Right) Anterior column fracture

 

 
Posterior wall and posterior column acetabulum fractures

(Left) Posterior wall fracture
(Right) Posterior column fracture

 

 
Transverse and T-shaped acetabulum fractures

(Left) Posterior wall transverse (across) fracture (Right) T-shaped fracture

 

Cause

An acetabular fracture results when a force drives the head of the femur against the acetabulum. This force can be transmitted from the knee (such as hitting the knee against the dashboard in a head-on car collision) or from the side (such as falling off a ladder directly onto the hip). Depending upon the direction of the force, the head of the femur is sometimes pushed out of the hip socket, an injury called hip dislocation.

When the fracture is caused by high-energy impact, patients often experience extensive bleeding and have other serious injuries that require urgent attention.

Acetabular fractures are sometimes caused by weak or insufficient bone. This is most common in older patients whose bones have become weakened by osteoporosis. Although these patients do not often have other injuries, they may have complicating medical problems, such as heart disease or diabetes.

Symptoms

A fractured acetabulum is almost always painful. The pain is worsened with movement.

If nerve damage has occurred with the injury, the patient may feel numbness, weakness, or a tingling sensation down the leg.

Doctor Examination

Physical Examination

Emergency Stabilization

Patients with fractures caused by high-energy trauma will almost always go or be brought to an urgent care center or emergency room for initial treatment because of the severity of their symptoms.

If the fracture is due to high-energy trauma, there may also be injuries to the head, chest, abdomen, or legs. If there is significant blood loss, it may lead to shock—a life-threatening condition that can result in organ failure.

Physical Examination

Your doctor will perform a thorough examination of your pelvis, hips, and legs. He or she will also check to see if you can move your ankles and toes and feel sensation on the bottom of your feet. In some cases, nerves may be injured at the same time that the acetabulum is fractured.

You doctor will also carefully examine the rest of your body to determine if you have received any other injuries.

Imaging Studies

X-rays. These studies provide images of dense structures, such as bones. X-rays of acetabular fractures are taken from a number of different angles to show the pattern of the fracture and how out of place the bones are (displacement).

Computed tomography (CT) scans. Because of the complex anatomy of the pelvis, a CT scan is commonly ordered for acetabular fractures. The scan will provide your doctor with a more detailed, cross-sectional image of your hip and can be helpful in preoperative planning.

 
X-ray and 3-dimensional CT reconstruction of an acetabular fracture

(Left) This x-ray shows a fracture of the front “wall” of bone supporting the hip socket. (Right) The cracks and uneven surfaces of the same fracture are shown more clearly in this 3-dimensional CT reconstruction.

 

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