Income is a powerful predictor of a patient's risk of readmission following elective spine surgery, according to a Houston Methodist-led study that raises questions about federal reimbursement policies that don't take social determinants of health into account.

The study also found that a neighborhood's diabetes prevalence and access to primary care providers predicted readmission risks. But income had by far the greatest impact — the odds of readmission were 11 times higher for patients with incomes below $31,000 compared to those with incomes greater than $62,000.

"We had suspected that income would affect surgical outcomes, but an 11 times odds ratio — essentially an 1100% increase in risk — is astonishing," says Dr. Saifi, a Houston Methodist orthopedic spine surgeon and the study's primary investigator. "We intuitively know that socioeconomic status affects a variety of outcomes, but such a stark difference in something as tangible as readmission rates following surgery merits significant national attention."

By contrast, Dr. Saifi notes, the most a variable typically increases readmission odds in studies is in the 1.5 to 2.5 range.

Findings from the study, published March 2 in the Journal of Bone and Joint Surgery, are important because the Centers for Medicare & Medicaid Services penalizes hospitals for high readmission rates in some patient groups.

Race and other social determinants of health

Black patients in the study had disproportionately higher readmission rates, making up 21% of patients and 35% of readmissions. Once adjusted for income, however, the researchers found that race was only a significant predictor only among those with estimated annual income below $31,000.

"Many studies have investigated racial disparities in isolation, but we wanted to study the root cause of racial disparities and other social determinants of health," says Dr. Saifi. "There is a complex interaction between how patients fare after medical treatment and their social determinants of health, including economic stability, neighborhood, education and access to quality health care."

The other social factors identified as predictors of readmission risk also had a significant effect. Patients with a high prevalence of diabetes in their neighborhood — an indicator of living in a food desert with limited access to healthy food — were three times more likely to face readmission. Patients living in neighborhoods with limited access to primary care providers were 1.4 times more likely to be readmitted.

For every decile increase in the Area Deprivation Index of the patient's census tract, the risk of readmission went up 40%.

"Taken as a whole, our findings suggest that disparities in spine surgery outcomes are inextricably linked to social determinants of health," says Dr. Saifi. "For most patients, financial resources are the most important factor in this study. It's pretty unambiguous."

Spine surgery interventions should preserve access to care

In the study, Dr. Saifi and his colleagues discuss implications for the Medicare Hospital Readmissions Reduction Program (HRRP), which fines hospitals whose readmission rates exceed current standards.

"Although the social factors affecting readmission risk are outside of a hospital's purview, they may be just as important as the intraoperative and perioperative clinical predictors of readmission," Dr. Saifi explains. "Unless HRRP and other value-based care initiatives can adequately account for this, our concern is that providers who take care of a larger portion of Medicaid patients will be unfairly penalized, and lower income patients may face even more limited access to care."

The HRRP does not currently include elective spine surgeries but is expected to in the future. The program considers age, sex and diagnoses in calculating expected readmission rates — factors not found to be significant in this study.

Next steps

Using this and other similar studies as a diagnostic tool, the researchers hope new interventions and policies addressing the underlying issues can be identified.

One potential intervention Dr. Saifi is planning to initiate is a nurse navigator program for patients at high risk of readmission.

"Nurse navigators have been tremendously positive for cancer patients, and we think a similar program designed to guide high-risk patients through their surgical journey could potentially reduce readmissions due to economic disparities," Dr. Saifi says.

From a policy perspective, Dr. Saifi points out that a large number of studies have shown that health outcomes are correlated with the density of primary care providers in one's neighborhood.

"Enhanced access to quality primary care means patients are coming to surgeons healthier and better prepared for their procedure," says Dr. Saifi. "We need to be looking at ways to support primary care providers, particularly those serving underserved communities, because that will benefit everybody — the patients, the physicians and the system as a whole."

Dr. Saifi is the C. James and Carole Walter Looke Chair in Orthopedic Spine Surgery and the author of over 50 peer-reviewed research publications. Prior to joining Houston Methodist, he was the director of Clinical Spine Research and a senior fellow at the Leonard Davis Institute of Health Economics at the University of Pennsylvania.