Physician Self-Referral and Imaging Use Appropriateness: Negative Cervical Spine MRI Frequency as an Assessment Metric

Discussion

The purpose of this study was to evaluate the differences in the use of cervical spine MR imaging between 2 groups of physicians, 1 with a financial interest in the imaging equipment used and 1 without. Our results demonstrate a 17.3% increased negative examination rate among patients referred by the physician group with a financial interest in the imaging equipment used (P = .006). Therefore, we reject the null hypothesis number 1. This suggests that there may be a reduced threshold for obtaining cervical spine MR imaging in the presence of a financial incentive, whether conscious or unconscious.

A wealth of literature exists on the topic of physician imaging self-referral. Many of these prior studies have attempted to compare use between 2 physician groups based on Medicare billing data.^19,20 Criticism of this method has often centered on an inability to adequately assess the appropriateness of imaging use and on the failure of the method to account for the many complexities driving use, such as differences in disease severity between patient groups. Indeed, accurately evaluating the relationship between imaging self-referral and financial incentive is extremely challenging and would require consideration of a multitude of factors including patient populations, referral biases (specialist versus primary care), clinical setting (outpatient versus hospital), disease prevalence, variations in diagnostic standards (discordant “grading” of severity), differences in imaging protocols and equipment, and differences in terminology used by interpreting radiologists.

Our study used a recently developed method to examine imaging self-referral that is focused on use appropriateness rather than a simple count of use per patient. Rather than reviewing billing data or imaging indications, we analyzed the final diagnoses on imaging examinations, thereby helping to control for differences in the severity of disease between different referring physician groups (FI and NFI). This method for comparing patient cohort similarity was used in several prior publications.^21⇓–23 Furthermore, a single small academic radiology group interpreted all examinations from both referring physician groups; this helps to control for radiologist interreader variation. Additionally, because this radiology group did not own any of the imaging equipment, there was no confounding financial interest.

We found no statistically significant difference in the average number of abnormalities per study with positive findings or in the number of positive levels per scan between the NFI and FI groups. Additionally, there was no significant difference in the rates of neuroforaminal stenosis, disk bulge, or facet degenerative change. This similarity in the abnormality rate per positive scan confirms the null hypothesis number 2 and suggests that the 2 patient groups had a comparable prevalence of pathology. Assuming that abnormalities found on studies with positive findings act as surrogates for the disease prevalence within both patient populations, the 2 groups appear to significantly differ only in their rates of cervical spine MR imaging studies with negative findings. We suspect that the divergent negative examination rate may reflect differences in decision-making in patients presenting with cervicalgia, particularly in regard to the threshold for acquiring imaging.

It is of particular interest that the FI group patients were more likely to receive concomitant shoulder MR imaging (P = .02). Because it is often challenging to differentiate between a cervicogenic and rotator cuff etiology for upper extremity pain, this clinical challenge was likely present in both patient populations.²⁴ If patients in the FI group had a larger prevalence of shoulder pathology than the NFI group, this might lead to an increased rate of positive concomitant shoulder MR imaging findings. However, this was not the case. In fact, patients in the FI group were more likely to have normal findings on shoulder MRI (33.3% for FI versus 9.1% for NFI, P = .22). Furthermore, comparing the subgroups of patients that underwent both cervical spine and shoulder MR imaging revealed that FI patients were also more likely to have negative cervical spine MR imaging findings. Finally, 9 patients in the FI group had negative findings on both examinations versus no patients in the NFI group. These findings, while somewhat limited by the small sample size, demonstrate increased use of concomitant shoulder MR imaging in the FI group and suggest a trend toward considerably increased negative examination rates in keeping with the cervical spine MR imaging data.

There were several limitations to this investigation. First, the inherent complexities of both cervicalgia and cervical spine degenerative changes make it difficult to define a “true-positive” examination. This challenge is pervasive throughout daily clinical practice. For instance, confirming a causal relationship between suspected imaging findings and a patient's pain often requires feedback in the form of targeted treatment. While even “mild” degenerative changes can be symptomatic, an objective demarcation for positive examination findings was a prerequisite to investigation. It is possible that establishing a different threshold for positive examination findings or considering alternative pathologies could have led to different results. However, we chose to define severe degenerative change as positive because these findings are more likely to be causes of pain that are clinically important and result in therapy, such as steroid injections or surgery. A second limitation is the relatively limited number of concurrent shoulder MR imaging examinations, hindering the ability to achieve statistical significance in the analysis of components of this subset of our data. Additionally, we did not compare insurance status, ethnicity, or socioeconomic status between the 2 groups because these data were not available for review. Finally, there was a statistically significant difference in age between the 2 groups (54.3 for NFI, 48.4 for FI). This required the use of ANCOVA with age as a covariate to account for the known increased prevalence of spine degenerative changes with advanced age.

Despite these limitations, this study clearly demonstrates an increased negative examination rate in the physician group that collected technical fees for the imaging equipment used. We believe that this apparent bias, whether conscious or unconscious, is an important consideration when health care costs, more specifically medical imaging costs, are analyzed. An excessive negative scan rate on the order of 15%–20% is a considerable financial burden when extrapolated nationally. To date, the across-the-board cuts to imaging reimbursements have done nothing to address this bias and have, instead, placed future access to advanced imaging in jeopardy. Similar findings have previously been reported in the lumbar spine, shoulder, and knee.^21⇓–23 These findings require validation across other geographic regions and medical practices.

The observed bias toward increased use of cervical spine MR imaging does not, by itself, prove intended overuse for profit. It is possible that other factors are at play influencing 1 physician group to image more frequently. Such considerations might include an imaging-intensive practice pattern less reliant on physical examination findings, perhaps secondary to differences in training. Similarly, one might purport that younger physicians may be more familiar with the use of MR imaging in diagnostic evaluations because it was part of their training, while more senior physicians may be more comfortable with alternative diagnostic methodologies (physical examination, myelography). Many of these physician-related considerations may not be significant factors in this study because the 2 groups were highly similar in terms of mean years of practice and number of trained subspecialists and had nearly equal percentages of physicians who trained at the same residency program.

Physician order entry decision support (OEDS) software has been proposed as a mechanism for decreasing the incidence of unnecessary imaging examinations. OEDS has proved success and could potentially reduce the rate of negative examination findings in both referral groups by providing recommendations according to the American College of Radiology appropriateness criteria for cervical spine MR imaging.²⁵ However, in most cases, OEDS software does not include “hard stops” but rather allows referring physicians to override recommendations. Therefore, the FI and NFI groups would be able to continue to order examinations as they think appropriate. Furthermore, if practice patterns for either group involve order placement by clinic office staff, the appropriateness recommendations may be blindly overridden to follow attending physician requests.²⁶ For these reasons, it is difficult to discern how the addition of OEDS would influence the ordering practice patterns of our referral groups.