Patterns of Ordering Diagnostic Tests for Patients with Acute Low Back Pain

Acute low back pain is a common problem; during the course of a year, 7.6% of adult residents of North Carolina have an episode severe enough to disrupt their usual daily activities [1]. Back pain is a common reason for a visit to a primary care physician [2, 3]. The cost of care for back pain has increased substantially in the past 20 years; direct costs for inpatient and outpatient medical care are now more than $25 billion per year [4]. The availability of basic diagnostic technology, such as lumbar spine radiography, and sophisticated imaging tests, such as computed tomography (CT) and magnetic resonance imaging (MRI), has broadened in recent years. Recent federal guidelines have emphasized a conservative approach to the diagnostic evaluation of acute back pain [5]. In 1992 and 1993, we examined the patterns of current use of diagnostic tests in a representative sample of primary care and specialty health care providers. This research took place before the publication of the latest federal guidelines but after the publication of numerous articles discouraging the early use of diagnostic tests [6-9]. The Agency for Health Care Policy and Research guidelines [5] emphasize a conservative approach to diagnostic testing in the first month of back pain and recommend that lumbar spine radiography be reserved for patients with symptoms and signs of serious illness, such as neurologic signs, a history of cancer other than skin cancer, or weight loss. Our project, the North Carolina Back Pain Project, examined specialty-specific differences in treatment patterns and outcomes [10]. We examined the determinants of the use of diagnostic tests among the main types of practitioners who care for acute back pain: primary care physicians, chiropractors, orthopedic surgeons, and practitioners in group-model health maintenance organizations. We specifically wished to examine how three categories of factors affected the relative contributions to ordering tests: 1) demographic characteristics of the patient [such as age, race, and sex]; 2) clinical condition of the patient [such as presence of sciatica, level of pain, and presence of neurologic findings]; and 3) factors about the practitioner (such as specialty, access to and ownership of imaging equipment, and confidence in ability to diagnose and treat back pain). We hypothesized that use of diagnostic technology would be associated with the physician's access to or ownership of imaging equipment, severe pain in the patient, and functional impairment or neurologic abnormality in the patient. Methods Our study was done in North Carolina, the population of which is almost equally divided between urban and rural areas. Twenty-two percent of the population is black [11]. Almost 600 chiropractors practice in North Carolina, and previous research by our group [1] showed that 39% of persons who seek care for acute back pain first see a chiropractor. Practitioners We examined community practitioners who commonly treat patients with acute low back pain. Patients were randomly selected from medical and chiropractic licensure files and were recruited until enough practitioners were available in each of six strata: urban primary care physicians, rural primary care physicians, urban chiropractors, rural chiropractors, orthopedic and neurologic surgeons, and physicians and a few family nurse practitioners at a group-model health maintenance organization. We defined primary care physician as one who was in family medicine, general internal medicine, or general practice. Few osteopathic physicians practice in North Carolina. Neurosurgeons were sampled, but none had seen a substantial number of patients with acute low back pain. Because few orthopedic surgeons practice in rural areas, these surgeons were sampled statewide. Practitioners were eligible for the study if they 1) practiced in an ambulatory care setting more than half time and 2) saw patients with acute low back pain and no previous referral as part of their practice. Practitioners were aware of the overall purpose of the study but not of the specific outcome or utilization variables. Practitioners received $40 per recruited patient as compensation for time spent screening patients, obtaining consent, and completing baseline clinical evaluations. Of the eligible practitioners invited, an average of 74% agreed to participate (range, 65% of primary care providers to 87% of practitioners in the health maintenance organization and orthopedic strata). The number of practitioners in each stratum was as follows: 39 urban primary care physicians, 48 rural primary care physicians, 32 urban chiropractors, 32 rural chiropractors, 29 orthopedic surgeons, and 28 general and mid-level practitioners at the health maintenance organization. In 1993, at the conclusion of the study, practitioners were given a survey that examined practitioner and practice demographic characteristics, perceived treatment patterns, and treatment of hypothetical patients by clinical vignette. The vignettes had previously been used to assess interspecialty diagnostic and therapeutic aggressiveness in a nationwide survey [12]. The study design allowed us to examine practitioner response to clinical vignettes and the relation of this response to clinical behavior with similar actual patients seen in the practitioners' offices. The vignettes asked practitioners to indicate whether they would order CT or MRI for three patients: one with sciatica and a diminished ankle reflex, one with chronic back pain, and one with acute back pain and unremarkable results on a physical examination. The following are the three vignettes: 1. Acute sciatica: A 35-year-old auto mechanic presents with a 4-day history of severe acute low back pain with radiation to the posterior calf and lateral foot. He has some sensory deficits in this distribution and a diminished ankle reflex but has no motor weakness. Straight-leg raising is limited to 45 degrees in the affected leg. Plain x-ray of the lumbar spine is normal except for postural changes suggesting muscle guarding. 2. Chronic back pain: A 50-year-old homemaker presents with a 3-year history of intermittent, excruciating low back pain. She has seen other doctors and chiropractors during this period but was disappointed with the results of care. She currently has severe back pain but there is no radiation to the legs, and physical examination reveals a limitation of lumbar spine flexion. Plain lumbar spine films show osteophytes at several vertebral levels but no disc space narrowing. 3. Acute back pain: A 28-year-old woman who runs her own catering service complains of having acute severe low back pain for a week. The pain is not radiating but is so severe she has been unable to work for the past 5 days. She is anxious to return to her usual activities but feels immobilized by the pain at present. Physical examination reveals markedly limited anterior flexion and left paraspinous tenderness and a normal neurologic examination. Lumbar spine films are normal. Two hundred eight practitioners agreed to participate in our study, 188 (90%) recruited at least one patient, and 162 returned completed surveys. Clinicians who contributed no patients reported that they saw few patients with acute back pain in their practices. Patients Practitioners invited consecutive patients with acute low back pain to participate in the cohort study. Patients were eligible if their current episode of back pain had lasted for less than 10 weeks and if they had not previously received care for the current episode of pain, had never had back surgery, had no history of metastatic cancer, were not pregnant, owned a telephone, and spoke English. Patients were the unit of analysis when the outcome was patient-oriented; the practitioner was the unit of analysis when the analysis was based on the practitioner survey. Practitioners obtained patient consent and gathered minimal information on the history and results of physical examination at the initial office visit. Twice weekly, we obtained the names and telephone numbers of the patients with back pain. Personnel from the University of North Carolina Survey Research Unit conducted all interviews. No attempt was made to influence the practitioners' diagnostic tests or treatments; our study was observational. Staff of the practices kept lists of the recruitment of patients into the cohort, thereby allowing assessment of approximate recruitment rates. Fifty percent of patients with back pain seen in the offices were eligible for the study; only 8% of those who were eligible refused enrollment. The main reasons for ineligibility were chronic pain and previous treatment of the current episode of pain. Patients received $20 for their time spent responding to the many surveys. They were told that the study was to examine how long back pain usually lasts and the types of treatments used. The Survey Research Unit contacted patients by telephone shortly after the index visit. The median time from the index office visit to the baseline telephone interview was 6 days (range, 0 to 62 days). Data Analysis Information on demographic characteristics, health care utilization, and functional status was collected at the time of the baseline interview and 2, 4, 8, 12, and 24 weeks after the baseline interview or until the patients declared themselves completely better. Functional status was examined by assessing time off from work and by using the Roland-Morris 23-item back disability scale, a validated subset of the Sickness Impact Profile [13, 14]. All patients were interviewed at 24 weeks. In telephone surveys, patients were asked about all care from all providers. Chart abstraction was used to gather details on care provided by the index practitioner. Charts were abstracted by a single research assistant. For key chart elements, reliability exceeded 0.9. Chart abstractors could not be blinded to practitioner type because specialty was often d