Health Workers Endangered by Mini-C Arm Imaging

Laird Harrison

March 09, 2018

NEW ORLEANS — Radiation scatter from orthopedic hardware can harm the eyes of first assistants during mini-C arm fluoroscopy, results from a new study suggest.

"I think the risk is significant," said Michael Groover, DO, from Grandview Medical Center in Dayton, Ohio.

Surgeons and first assistants should use the mini-C arm in the vertical position as much as possible, and wear lead-lined glasses and other protective clothing, he told Medscape Medical News.

Orthopedic surgeons frequently use the mini-C arm fluoroscopy during the implantation of metal devices, such as plates and retractors. Previous studies have measured radiation exposure from these procedures, and generally determined the levels to be safe.

However, few, if any, of these studies have taken into account the way x-rays are scattered by metal hardware, Groover said here at the American Academy of Orthopaedic Surgeons 2018 Annual Meeting.

To determine whether metal poses an increased risk, he and his colleagues positioned an InSight 2 mini-C arm (Hologic) over a hand table set up to fix forearm or wrist fractures.

People took positions around the table that would typically be occupied by a nurse, scrub technician, anesthesiologist, first assistant, and surgeon. Parallel plate radiation detectors measured the radiation at each person's eyes, thyroid gland, chest, and gonads, and the hands of the person in the surgeon's position. A leg of lamb lay in the center of the x-ray beam.

Groover and his colleagues measured radiation with the mini-C arm in the horizontal position, first without any hardware in the leg of lamb, and then with a 3.5 mm stainless steel plate and six cortical screws on the anterior aspect of the lamb leg. They repeated the procedure with the mini-C arm in the vertical position.

Table 1. Direct-Beam Radiation Levels

Mini-C Arm Position Without Plate (mrem/min) With Plate (mrem/min)
Horizontal 893.0 121.0
Vertical 273.0 245.5

 

With the plate in place and the arm horizontal, the radiation bounced off the plate and hit the hands of the surgeon and the eyes of the first assistant with high doses of radiation. In fact, because they were so close to the plate, the first assistant's eyes and surgeon's hands received doses that were higher than the direct beam passing through the leg of lamb and traveling into the collector tube on the other side.

Table 2. Radiation Exposure With the Mini-C Arm in the Horizontal Position

Anatomic Site Without Plate (% of Direct Beam) With Plate (% of Direct Beam)
Surgeon    
Left hand 0.025 1.653
Right hand 0.182 1.653
Eyes 0 0
Thyroid 0 0
Chest 0.0545 0
Gonads 0 0
First Assistant    
Eyes 0.016 2.893
Thyroid 0.034 0
Chest 0 0
Gonads 0 0

 

None of the other people in the room received measurable doses of radiation because they were far enough away from the mini-C arm. And because hands are relatively resistant to the effects of radiation, the researchers do not consider the exposure to the surgeon's hands to be dangerous.

The real danger is the accumulation of radiation. The lens of the eye is the most sensitive tissue in the body.

But the first assistants' eyes are another matter. "The real danger is the accumulation of radiation," said Groover. "The lens of the eye is the most sensitive tissue in the body."

And, according to the researchers' calculations, exposure to the first assistant's eyes exceeded the annual 2000 mrem recommended by the International Commission on Radiological Protection.

The concern is more than theoretic. A previous report demonstrated that the people exposed to the most radiation during catheterization procedures were the most likely to have opacities in their lenses — an indication of cataracts (J Vasc Interv Radiol. 2013;24:197-204).

In the vertical position, the radiation exposure to the first assistants' eyes was only a fraction of the exposure in the horizontal position. But the horizontal position is commonly used because it is convenient for positioning the patient's limb, Groover explained.

"People should change the position, move out of the way, or wear leaded eyewear and other protective equipment," including a leaded apron and a thyroid shield, he said.

This study is important because orthopedic surgeons are using more fluoroscopy than in the past, partly because of the growing popularity of procedures that use smaller incisions, said Robert Orfaly, MD, from Oregon Health and Science University in Portland.

"If we are not able to directly see the anatomy, we use radiation to guide us," he told Medscape Medical News. "This study really makes us think twice about how important it is to get lead-lined glasses."

Lead-lined Glasses Expensive, Cumbersome

Most hospitals do not provide the glasses, which are expensive, so people involved in mini-C arm fluoroscopy don't typically wear them. In addition, they are heavy, distort vision, and must be specially made if the wearer requires prescription lenses. "Personally, I don't use them consistently because I find the increased glare and distortion distracting, particularly for long cases," Orfaly said.

An alternative to reduce exposure from mini-C arms is a targeting system that can help position hardware without continuous imaging, he suggested.

The leg of lamb did not appear to be harmed by the radiation, but it ultimately sustained more damage than any of the researchers did because they took it home and ate it after the experiment.

Groover and Orfaly have disclosed no relevant financial relationships.

American Academy of Orthopaedic Surgeons (AAOS) 2018 Annual Meeting: Abstract P0724. Presented March 8, 2018.

Follow Medscape Orthopedics on Twitter @MedscapeOrtho and Laird Harrison @LairdH

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