The Relationship between Low Back Magnetic Resonance Imaging, Surgery, and Spending: Impact of Physician Self-Referral Status

Rapid growth in medical imaging, particularly advanced and costly imaging using magnetic resonance (MR) and computed tomography equipment, has given rise to a range of questions about the value of these procedures (Iglehart 2006; Medicare Payment Advisory Commission 2009). Significant bodies of research demonstrate the ability of new imaging technologies to contribute information valuable to patient care. At the same time, there are also concerns that imaging may be overused in some contexts. Increasing use of imaging has also been associated with the potential for “treatment cascades” (Deyo 1994; Jarvik et al. 2003) in which the use of imaging leads to the use of subsequent procedures that are of low value to the patient and, but for receipt of the imaging procedure, would never have been done. While the conceptual case for imaging-driven treatment cascades is plausible, whether they are important in practice is not well understood. One difficulty in studying treatment cascades is the ease with which unobserved characteristics of patients can bias analyses of the relationship between imaging receipt and use of subsequent treatments. Patients with more serious health conditions, who are most likely to receive treatments, may also be the most likely to get imaging procedures. If this happens, analyses that cannot adequately account for patient health would produce biased estimates. This paper examines the relationship between receipt of magnetic resonance imaging (MRI) for back pain and the subsequent use of back surgery. This is an area that is associated with substantial costs—an estimated U.S.$80 billion in direct spine-related expenditures are incurred annually in the United States (Martin et al. 2008). It is also a classic setting for discussion of imaging treatment cascades. Imaging for low back pain without indications of serious underlying conditions has not been shown to improve clinical outcomes (Chou et al. 2009b). Since 1994, guidelines (Bigos, Bowyer, and Braen 1994) have recommended a cautious approach to the use of low back imaging because of the weak correlation between radiographic findings and clinical symptoms (Jensen et al. 1994; Jarvik and Deyo 2002) and high likelihood for acute low back pain to improve without treatment (Pengel et al. 2003). And yet rates of MRI for low back problems have increased substantially over time (Smith-Bindman, Miglioretti, and Larson 2008); one study estimated lumbar MRI use increased in the Medicare population by as much as 300 percent between 1994 and 2006 (Deyo et al. 2009). Use of MRI is often associated with receipt of back surgery, in two dimensions. On one hand, patients for whom surgery is indicated often receive MRI as a precursor to surgery. On the other hand, importantly, research has shown that many people with no back pain have anatomical features in their back that appear abnormal on MRI (Jarvik and Deyo 2002). Individuals with back pain who receive MRI thus run a nontrivial risk of having a “positive” finding on MRI. The abnormality identified may not be the cause of the back pain, but the existence of the abnormal MRI finding can easily create an imperative to undertake treatments, including surgeries, to correct the abnormality. In the end, many of these surgeries, aimed at something that was not causing the pain, are ultimately unsuccessful at relieving the symptoms, but they do entail large costs as well as other risks for the patient. Two randomized controlled trials have assessed the relationship between the use of low back MRI and low back surgery or expenditures. In both trials, there was a trend toward more surgery and higher costs among patients receiving early spinal MRI (compared with those receiving standard X-rays or delayed spinal MRI), but there was insufficient power to detect a statistically significant difference (Jarvik et al. 2003; Gilbert et al. 2004). Previous work has also shown that increased availability of MRI equipment in geographic areas is associated with higher rates of MRI and surgery among low back pain patients in the area (Baras and Baker 2009). This study, however, could not address linkages between MRI receipt and surgery use directly. Its suggestion of a link provides important motivation for this study, which attempts to directly investigate the strength of the connection. We use a novel methodology to identify and explain the impact of receipt of low back MRI on subsequent use of procedures. Previous research has shown that nonradiologist physicians who acquire their own MRI equipment perform more MRI scans on their patients after they acquire the equipment than they did before they acquired (Hillman et al. 1990; Radecki and Steele 1990; Hillman et al. 1992; United States General Accounting Office 1994; Gazelle et al. 2007; Baker 2010). This increased use of MRI scanning appears to occur without meaningful changes in the characteristics of the patients in the doctors' practices. As such, acquisition of MRI equipment may provide a useful opportunity to study the impact of receiving an MRI scan on use of subsequent treatments. If physician acquisition of MRI leads patients with low back pain seen after acquisition to be more likely to receive MRI than patients seen before acquisition, studying the receipt of back surgery by patients before and after acquisition of the equipment can provide a potentially unbiased estimate of the impact of MRI receipt on use of low back surgery.