Spondylolysis Part II: Imaging and Radiation Safety
May 21, 2013 7 Comments
I’ve wanted to return to the issue I wrote about in a blog post a week ago, “Spondylolysis: Issues of Incidence and Imaging, Part I.” In that post and this one, I have been primarily looking at a provocative new study published in the Journal of Pediatric Orthopaedics, “Imaging Modalities for Low Back Pain in Children: a Review of Spondylolysis and Undiagnosed Mechanical Back pain.”
Single Photon Emission Computerized Tomography, or SPECT scans, like the image to the left showing bilateral L5 spondylolyses, are highly sensitive for detecting spondylolysis but expose the patient to radiation. This is something I have known, of course, since training. In my current practice at Nationwide Children’s Hospital Division of Sports Medicine I and my group of fellow clinicians focus on youth athletes, and so we see large numbers of potential ‘spondys’ and, correspondingly, order a large number of diagnostic images. In 2012 we saw 548 new patients whose chief complaint was back pain; we ordered 227 SPECT images for ‘back pain’ in that same year.
I share those numbers with the readership to give some context to the interest and concern with which I read the study article authored by a group from Children’s Hospital of Philadelphia. The bulk of the study’s original data looked at issues of the incidence of spondylolysis in the CHOP population, numbers that I have taken some issue with. The secondary focus of the study looked at one outcome the authors published regarding the issue of imaging for spondy. In their series of 2846 patients presenting with “mechanical low back pain” over an 8-year study period, they report that 73 of 88 patients (84.3%) that had a spondylolysis that received a bone scan had a positive scan. This number of 84.3% relates to the sensitivity of the bone scans used in the study (it is not reported how many of these might have been SPECT scans vs. other nuclear medicine bone scans). It also represents a frequency of advanced imaging much different than our center.
What really drew my attention and is likely to make me change my practice is the authors’ transition to a discussion of radiation safety. The CHOP group details radiation absorbed doses for a variety of studies employed in detecting a spondy: 2-view plain films (AP and lateral); 4-view plain films (AP, lateral, and obliques); CT scans; and bone scans. What I learned is that the radiation effective dose for a 10 – 14.9 year old (our typical patient) is nearly 7 milliseverts (mSv) whereas a CT scan is a bit more than 1 mSv and 2-view plain film series is just under 1 mSv. Furthermore, the organ-specific dose for the urinary bladder is a whopping 50.3 milligrays (mGy), while a CT scan exposes the same organ to only about 1 mGy (though it exposes the colon to 6.6 mGy); this makes sense, of course, as in our hospital the SPECT protocol involves IV administration of technetium, which will eventually be excreted by the kidneys and stored in the urinary bladder until the patient voids.
What do all these numbers mean? Indeed, I hope the readers share their thoughts as the discussion of resource utilization and radiation safety is an on-going issue, and multiple viewpoints should factor in the debate. As has been reported in many recent studies, the use of radiation-based diagnostic imaging has exploded over the last couple of decades in the United States, at least. One study focusing on the increased use of CT scans in the United States has estimated that 2% of all future cancers will be caused by radiation from medical studies.
These are sobering numbers. On balance, there is evidence that many of the studies we more routinely order, such as plain films, have comparable radiation levels as one might encounter with background, natural exposures. But I don’t want to be glib here: there is no debating the “ALARA” principle, which states that all radiation use should result in exposures “as low as is reasonably achievable.” There is no biological threshold below which radiation is ‘safe.’ The less one receives in life, the better.
In the world of sponylolyses, the holy grail of imaging might be the MRI: a group in Japan published in the American Journal of Sports Medicine in 2012 their data on the use of MRI in detecting occult lumbar spondylolysis in young athletes. I certainly think that it is important to detect and manage properly this condition in a young athlete, but at what cost? The radiation exposure issues give me great pause. I definitely plan on working with our hospital radiology department in setting up an MRI protocol for detecting spondys.
What do the readers think? Please comment on this blog. I’ll be responding to all comments. Also, take a look at the new poll on our journal’s web site, in the lower right corner of that web page. We haven’t even begun to talk about the controversy in treating spondylolyses in young athletes. How do you treat your athletes? Do you brace or not brace? Take the poll!