Radiation exposure associated with CT preoperative planning.

The effective dose in millisievert (mSv) is the risk-based metric for radiation exposure. A millisievert is defined as "the average accumulated background radiation dose to an individual for 1 year, exclusive of radon, in the United States." 1 mSv is the dose produced by exposure to 1 milligray (mGy) of radiation.

The radiation dose for a conventional shoulder X-ray series is reported as 0.01 mSv (see this link) 

The effective doses from diagnostic CT procedures are typically estimated to be in the range of 1 to 10 mSv (100 to 1000 times the dose of plain shoulder x-rays). It has been suggested that such exposures may be associated with a small but increased radiation-related risk of mortality (see this link).

In Comparison of Simulated Low-Dose and Conventional-Dose CT for Preoperative Planning in Shoulder Arthroplasty the authors state, "Computed tomography (CT) scans have become increasingly popular in preoperative planning for reverse and anatomic total shoulder arthroplasty. These scans are often used in conjunction with software that allows surgeons to plan bone preparation and optimal implant position. While the use of shoulder CT scans can improve glenoid-component positioning, there is the undesirable side effect of ionizing radiation exposure."

They reported the volumetric CT dose index (CTDI) expressed in milligrays for 18 patients having shoulder CT scans obtained for preoperative arthroplasty planning, all exceeding CTDI of 10 mGy.

Out of concern for the risks of radiation exposure, they sought to evaluate the utility of simulated low-dose CT images for preoperative planning using manual measurements and common preoperative planning software using reduced radiation doses (RD) levels of 75%, 50%, and 25%.

They found that at all radiation dosage levels evaluated, the preoperative planning software successfully segmented the CT images. Semiautomated software measurement of 25% RD images was within tolerances in 99.1% of measurements; for 50% RD images, within tolerances in 96.3% of measurements; and for 75% RD images, within tolerances in 100% of measurements. Manual measurements of 25% RD images were within these tolerances in 95.1% of measurements; for 50% RD images, in 98.8% of measurements; and for 75% RD images, in 99.4% of measurements.

They concluded that simulated lower-dose CT images were sufficient for reliable measurement of glenoid version, glenoid inclination, and humeral head subluxation by preoperative planning software as well as by physician-observers. And that the adoption of low-dose techniques in preoperative shoulder CT may lower the risk of radiation exposure for patients undergoing shoulder arthroplasty, without compromising image quality.

Comment: Even with a 25% reduction in radiation dosage, it is evident that the CT scans used in preoperative planning subject the patient to substantially greater radiation exposure than for plain radiographs. Two questions arise:

1. For shoulders with straightforward anatomy, such as that in one of the case examples from the article shown below, how much increased value to the patient is there in three dimensional CTs in comparison to standardized plain radiographs (see this link)?

2. Since the purpose of 3D CT planning is to achieve a certain component position, is a second CT scan required to document the degree to which the preoperative plan is realized? Alternatively, a preoperative and postoperative set of plain films seems adequate to the task in the great majority of cases (see this link). 

Future clinical research will be required to determine the appropriate use criteria for 3D CT planning, i.e. which patients with shoulder arthritis benefit sufficiently from 3D CT planning to offset its increased risk and cost.

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Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link).

How to x-ray the shoulder (see this link).

The ream and run procedure (see this link).

The total shoulder arthroplasty (see this link).

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

The smooth and move procedure for irreparable rotator cuff tears (see this link).

Shoulder rehabilitation exercises (see this link).

CT scans and their radiation risk

There is currently great enthusiasm for using computer tomographic (CT) scans to create detailed images of the arthritic shoulder. While CT scans may be necessary in unusually complex cases, we find that for the great majority of patients having surgery for shoulder arthritis a standard set of x-rays including the axillary "truth" view provides all the needed information as pointed out in this link.

Here are some examples of the preoperative anatomy of some arthritic shoulders as seen on standardized axillary views

and some preoperative and postoperative comparisons of standardized axillary views, showing the restoration of the desired anatomic relationships in a shoulder with severe arthritis.

Two recent articles that have discussed the potential risks associated with radiation prompted this blog post:

An Estimation of Lifetime Fatal Carcinogenesis Risk Attributable to Radiation Exposure in the First Year Following Polytrauma A Major Trauma Center’s Experience Over 10 Years

These authors point out that the utilization of medical imaging continues to rise, including routine use in major trauma centers. Their aims  were to estimate the amount of radiation exposure from radiographic imaging and the associated fatal carcinogenesis risk among patients treated for polytrauma at 1 institution. 2,394 patients, with a mean injury severity score of 29 were included in their analysis. The mean total radiation dose received was 30.45 mSv and the median dose was 18.46 mSv. One hundred and fifteen patients received >100 mSv of radiation. The total patient group had a 3.56% mean risk of fatal carcinogenesis of any type that related solely to medical exposure of radiation as a result of their injuries. In their lifetime, 85 patients would be expected to develop cancer as a result of medical imaging that they had undergone in the year following their accident. They caution that this study does not provide an actuarial analysis: it is unknown how many patients in the study actually went on to develop cancer.

and How Can We Reduce Cancer Risk Due to Medical Imaging?

We also note a quote from the well-known book The Gene: An Intimate History: In 1926 Herman Muller "exposed a cohort of flies to an even lower dose of radiation...Even a cursory look confirmed a striking result: the newly born flies had accumulated mutations -- dozens of them, perhaps hundreds." (page 115). 

In Radiation Exposure from Musculoskeletal Computerized Tomographic Scans the authors point out that the radiation dose from a shoulder CT scan exceeds that of 25 chest x-rays.

Where does all this leave shoulder patients and shoulder surgeons? First we need to recognize that x-rays and particularly CT scans subject the body to ionizing radiation which can increase the risk of mutations and cancer. Second, each CT scan subjects the patient to 26 times the radiation of a standardized axillary view. Third, it has yet to be demonstrated that patients with preoperative CT scans realize better clinical outcomes from shoulder arthroplasty than those having only the standard preoperative x-rays. Fourth, we suggest that it is reasonable to reserve the use of CT scans for the special cases of glenohumeral arthritis in which the needed information cannot be gained from standard x-rays.

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How you can support research in shoulder surgery Click on this link.

Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link).

How to x-ray the shoulder (see this link).

The ream and run procedure (see this link).

The total shoulder arthroplasty (see this link).

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

The smooth and move procedure for irreparable rotator cuff tears (see this link).

Shoulder rehabilitation exercises (see this link).

Glenoid component failure, osteolysis - sterilized by radiation in air

We had an interesting day yesterday in the OR. Among other revisions, smooth and moves, and ream and runs, we revised two Tornier total shoulders. The first case had already had a revision (elsewhere) of a Tornier total shoulder on the left shoulder for a failed glenoid. The right arthroplasty had been done in 2005. In 10/2012 we saw him for the first time because of pain in the right shoulder. His x-ray is shown below, revealing glenoid osteolysis.

In 5/2013 he decided to proceed with revision. At that time his films showed a dramatic increase in the osteolysis as well as evidence of a shift in the position of the glenoid component markers.

At surgery his component was loose and worn.

There was no obvious evidence of infection, but the shoulder was filled with non-inflammatory reactive tissue, such as the below.

We obtained multiple cultures for Propionibacterium and other bacteria before administering Ceftriaxone and Vancomycin (which we will continue for 6 weeks followed by a year of oral antibiotics).

After a thorough cleanout, we reconstructed his shoulder using a press fit humeral prosthesis that articulated with the rim of his residual glenoid. No glenoid bone graft was used. Post op we are starting him on our routine post-arthroplasty rehabilitation.

The second case had a Tornier total shoulder implanted in 2000. At the time of presentation to us, the radiographs, like the first case, showed massive osteolysis and glenoid component loosening.

The operative findings and the procedure were identical to the prior case. The postoperative films are shown here.

Comment: the surgical findings in these cases are consistent with either a Propionibacterium infection or with 'polyethylene disease' resulting from particles of poly released into the shoulder by component wear. Each of these glenoid components were not only loose, but the poly was degenerated suggesting that they may have been sterilized by gamma radiation in air. This is a problem previously noted in DePuy glenoids as well when the component was sterilized in air. The only way to distinguish them is by cultures of multiple samples (at least 5) of tissue and explants, holding them for three weeks and using multiple culture media.  For that reason we have both of these patients on the 'red' protocol of IV antibiotics via a PICC line for six weeks. If cultures are negative, we will discontinue antibiotics afterwards. Otherwise the patients will be on oral antibiotics for a year.

The humeral head prostheses have the largest diameter so that they will sit on the rim of the osteolytic glenoid. No glenoid bone grafting is used, but Vancomycin / allograft is used for humeral component fixation.

The histology on such cases usually looks like that shown below

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Is a CT scan necessary before doing a shoulder arthroplasty?

Some surgeons routinely obtain a CT scan before proceeding with a shoulder joint replacement. A CT scan adds an estimated $1000 to the cost of evaluating a shoulder for arthroplasty. In 2008, 47,000 shoulder arthroplasties were performed in the US and "The number of shoulder arthroplasties, particularly total shoulder arthroplasties, is growing faster than ever. " If, four years ago, a CT scan was obtained on each of these shoulders, the total cost would have been $47 million.

The effective dose of a computerized tomographic scan of the shoulder is 2.06 mSv. It has been pointed out that "computerized tomographic imaging of the spine or other anatomic structures in close proximity to the axial skeleton such as the shoulders, hips, or pelvis may subject the patient to significantly greater quantities of ionizing radiation. "

For these two reasons we avoid the routine use of CT scans before shoulder arthroplasty, instead relying on properly done AP and Axillary views.

Sometimes patients come to us with CT scans performed elsewhere, giving us the chance to see if additional information could be gained from them.

A recent example:

Here's the preop axillary view we obtained. It clearly shows a Walch B2 glenoid.

Here is the CT scan from elsewhere showing the same.

We performed a ream and run procedure on this shoulder. Two years later the patient rated his shoulder as 12/12 on the SST and had the axillary x-ray shown below - showing the conversion of the biconcave glenoid to a single stable concavity.

Our practice is to obtain CT scans only on the rare shoulder where the anatomy is not evident from plain films.

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shoulderarthritis@uw.edu.

Use the "Search the Blog" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty,  and rotator cuff surgery.

See the countries from which our readers come on this post.