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What is a 'crankshaft phenomenon,' and when does it occur?

Dr. Frank J. Schwab

New York, NY

Most types of scoliosis surgery involve a fusion of the affected levels in the spine. When this procedure is performed on the posterior portion of the spine, continued growth may occur on the anterior aspects of the spine. In a young patient, if significant growth occurs anteriorly following a posterior fusion, the spine may develop a progressive deformity (curvature) called "crank shaft".

Dr. W. Christopher Urban

Glen Burnie, MD

Crankshaft phenomenon refers to the circumstance where anterior (front) spinal growth continues despite a successful posterior fusion, causing a deformity along the levels of the original spinal fusion. It can occur after a posterior spinal fusion on a younger patient, since younger patients have continued growth in the front part of their spine. As the spine grows anteriorly, the posterior fusion acts as a tether and causes a rotational deformity. Strategies to prevent crankshaft phenomenon include to delay surgery, if the curve is not severe, or to do a combined front and back fusion.

Dr. Baron S. Lonner

New York, NY

Crankshaft phenomenon is a continued growth in the anterior (front) of the spine after a posterior fusion is performed in a young growing patient. This results in further rotation and even curvature of the spine despite a solid posterior fusion. Patients at greatest risk for this problem are under age ten with their growth centers indicating a large amount of remaining growth. We look at the growth centers at the hip socket, the triradiate cartilage, and the growth cartilage over the pelvic bone. The growth center along the pelvis allows us to predict remaining growth and is divided into four quadrants and labeled 0-4 with 5 indicating complete maturity and 0 indicating maximum remaining growth. This is termed the Risser sign. Patients who have Risser maturity of zero or one are at greatest risk for developing the crankshaft phenomenon.

Dr. James Mooney, III

Detroit, MI

"Crank shaft phenomenon" is an event that may happen in younger patients who have a fusion of the posterior spine only and still have significant growth at the anterior spine. This may cause the curve to progress despite an intact fusion posteriorly. The possibility of "crank shaft phenomenon" is one of reasons that anterior and posterior surgery is sometimes recommended in more immature patients.

Dr. Jean-Pierre C. Farcy

New York, NY
M.M.C. Spine Center

Crank shaft phenomenon is the continuation of growth with an abnormal spiral staircase appearance of the spine which was tethered by a posterior fusion. It occurs when a posterior fusion is performed on a young child before the growth spurt, far before skeletal maturity.

Dr. Robert W. Molinari

Rochester, NY

“Crank shaft phenomenon” is an expression used to describe cases where the front of the spine still grows after the back of the spine has been fused. This phenomenon is usually only seen in patients less than 10 years of age who have undergone a fusion procedure.

Dr. John T. Smith

University of Utah Department of Orthopaedic Surgery

A crank shaft phenomenon may occur when there is significant growth remaining at the time of scoliosis surgery. A crank shaft effect is a result of having the fusion on the posterior side of the spine, but there is anterior growth. Typically, we are concerned about this in children under 10 years of age, or when the triradiate cartilage, (a growth plate around the hip), is still open, indicating that a child has significant growth remaining. When crank shaft phenomenon is a concern, children require both anterior and posterior fusion to prevent it.

Dr. Patrick Bosch

Albuquerque, NM

“Crankshaft” is a term used to describe a situation that sometimes happens when a curve is fused only from the posterior approach and the remaining anterior growth makes the curve look worse. It is an issue in younger patients who have significant remaining growth.

Dr. Michael F. O'Brien

Denver Orthopaedics

A crankshaft phenomenon occurs when in spite of a solid posterior fusion, the anterior vertebral bodies continue to grow causing the scoliosis to progress during the rapid growth phase between 12 and 15 years of age. In patients older than 10 years of age this is typically not a problem.

Dr. David W. Polly, Jr.

Minneapolis, MN

Crankshaft phenomenon is when the front part of the spine keeps growing when the back part is fused. Usually it only occurs when we have to do the surgery in patients less than 10 years old.

Dr. Robert S. Pashman

Los Angeles, CA

Crankshaft phenomenon may occur in a very young patient who undergoes a posterior only spinal fusion for scoliosis. Although the back of the spine is fused, the front of the spine continues to grow causing the twisting characteristic of the fusion mass observed in crankshaft phenomenon.

Dr. Dennis G. Crandall

Mesa, AZ

When the back of the spine is fused but the front continues to grow (in patients 10 or younger), the spine continues to rotate and curve like a crankshaft on a car.

Dr. Stephen Ondra

Chicago, IL

Crankshaft phenomena will occur when the spine requires fusion before skeletal growth has been completed. The spine is restricted by the instrumentation. This is especially true in posterior fusions (back of the spine). The spine continues to grow in the front portion. This results in the spine shifting side to side to allow growth in the front while it is restricted in the back. The risk of this can be significantly decreased by waiting until a patient has neared skeletal maturity. If the surgery cannot wait, it is possible to come through the chest with a scope or an open incision to interrupt the growth plates in the front of the spine to stop growth there.

Dr. Thomas G. Lowe

Woodridge Orthopaedics & Spine Center, P.C.

A crankshaft phenomenon occurs in patient's who have had posterior instrumentation and fusion at a very young age, usually below age 10. It is not as common as originally thought. Surgery is generally not done in this age group. It is postponed until a later time by the use of bracing unless the curve is very severe. For patient's who are at high risk for this problem, which are very few in number, use of anterior instrumentation and fusion will prevent it.

Dr. Charles E. Johnston, II

Texas Scottish Rite Hospital Orthopedic Group

This is what happens when you have a posterior spinal fusion at a young physiologic age with significant growth remaining. The posterior fusion acts as a tether to growth on the posterior part of the spine, while the anterior part ( the side of the spine facing the lungs in the chest and the intestines in the abdomen) continues to grow. The result is that the spine spins around the posterior tether like a crankshaft, causing the scoliosis to recur even though the spine has already been fused.

The commentary above recounts the experiences of these physicians. Medtronic invited them to share their stories candidly. Keep in mind that results vary; not every patient's response is the same. Talk with your doctor to learn more about any products that are mentioned above.

It is important that you discuss the potential risks, complications and benefits of spinal surgery with your doctor prior to receiving treatment, and that you rely on your doctor's judgment. Only your doctor can determine whether you are a suitable candidate for this treatment.

  • Published: June 20, 2002
  • Updated: April 19, 2010