Saturday, July 30, 2016

Ask the Doctor: Why do you leave distraction device on so long?

CCA posts a monthly blog series called, "Ask the Doctor." You can submit your questions to Annie Reeves ([email protected]) and we will ask Dr. Earl Gage of Kids' Plastic Surgery in St. Louis to answer them. Thanks Dr. Gage for helping spread information and resources for our cranio families!

Ask the Doctor

Earl Gage, MD, Kids Plastic Surgery, MercyChildren’s Hospital
Ask The Doctor
Earl Gage, MD
Kids Plastic Surgery, Mercy Children’s Hospital – St Louis, MO

Question: My five year son had his frontal advancement procedure done one month ago. The doctor told us that it would take about two months for the halo to complete the process. Last week the doctor then made the decision to remove the halo because some of the hardware had loosened, a cord was damaged and one of the sites was getting infected.  He said the advancement was already done anyway. My question is if the halo completes its job when it doesn't need turning anymore why do they leave it on for such of long time?

Answer:  Distraction osteogenesis involves cutting a bone and then slowly lengthening the bone by applying a constant steady force. In order to understand the phases of distraction and why we leave the halo on even after the work of moving the bone is done, it helps to first understand what happens when a bone is broken and needs to heal.

When a bone is fractured, the body begins the healing process by stimulating cartilage and bone producing cells at both ends of the fracture to begin laying down new hyaline cartilage and woven bone in an effort to bridge the fracture gap. This new tissue spanning the fracture is called a callus and is relatively soft. Once the gap is bridged, the callus tissue is eventually replaced with stronger lamellar bone. Additional biologic changes and modifications of the bone occur until complete healing is accomplished. During the process of fracture healing, it is necessary to have good blood supply, good nutrition, good alignment of the fracture edges and good bone immobilization. Fracture healing often takes 4-6 weeks or longer.

Beginning in the early 1900’s some physicians realized that bone could be lengthened applying tension to the bone while in the callus phase of healing. If you lengthen the bone at just the right rate, you can continue to lengthen the bone at the callus while new bone is being formed just behind the callus.  In essence you stay just ahead of where the bone is becoming solid and stretch the soft stuff.

Once you have achieved your bone-lengthening goal, you then stop applying the lengthening force to the bone and instead try to provide stability and immobilization of the fracture so that bone healing catches up and the bone becomes strong. 

The reason, therefore, that there is a period of time after you are done turning the screws is to provide stability to the bones while the bone healing “catches up” and makes the bone solid and strong. This is called the consolidation phase of distraction and may take 4-6 weeks to allow full healing to occur. If the distractor is removed too early, while the bone is still healing and relatively soft, then there is a risk that you could lose some of your gains or that the fracture may not heal appropriately. 

Although we all want to have the distractor in place through consolidation, there are times when the distractor mechanism needs to be removed early. Reasons for early removal can include infection, malfunction or accidental dislodgement. Depending on when this occurs in the process of distraction and consolidation, the surgeon then has to make a judgment whether the bone is sufficiently solid to allow removal or if something else needs to be done to provide stability while the fracture continues to heal. A decision to put a new halo on is a decision based on risks and benefits of another surgery. From what you describe, it sounds as though your surgeon felt that things would be sufficiently stable to allow early removal.

I hope this helps answer your question, and I hope your son recovers well from his surgery.

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