Patient Factors Explain Most of the Variation in Function after Lumbar Spinal Fusion

Patient-reported functional outcomes vary considerably after lumbar spinal fusion surgery. A new study published in Spine suggests that this variability mainly reflects patient characteristics rather than differences in care provided by surgeons or hospitals.

“Variations in patient-reported outcomes [PROs] across hospitals and surgeons were mainly driven by differences in patient populations undergoing lumbar fusion, suggesting that PROs may not be useful indicators of hospital or surgeon quality,” according to the report by David R. Flum, MD, MPH, of the University of Washington in Seattle, and colleagues.


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The researchers analyzed variations in PROs among 737 patients (average age 63 years; 60% women) who underwent spinal fusion surgery between 2012 and 2018. The patients were enrolled in a statewide quality improvement collaborative called Spine COAP, which included about three-fourths of all spinal fusion procedures performed in Washington state. The surgeries were performed by 58 surgeons at 17 hospitals. The study focused on patient-reported functional improvement, based on the standard Oswestry Disability Index (ODI).

One year after spinal fusion, 58.7% of patients rated themselves as having improved functioning, based on at least a 15-point reduction (out of 100) on the ODI. “Minimal disability,” defined as an ODI score of 22 or less, was reported by 42.5% of patients.


Adjusting for Patient and Clinical Factors


Initial analysis suggested wide variation in outcomes by surgeon and hospital. For example, the percentage of patients reporting functional improvement ranged from about 44% to 79% at different hospitals, and 33% to 84% across surgeons.

But the variations were much narrower after adjustment for factors known to affect outcomes:

  • Patient-related factors: Age, smoking, insurance status
  • Clinical factors: Previous spine surgery, type of spinal disease, initial disability score

After adjustment, there were “no detectable statistical differences” in the outcomes of spinal fusion among hospitals or surgeons.

The effects of hospital and surgeon were larger among patients with a lower chance of improvement after spinal fusion, based on known risk factors. In contrast, for patients with a higher chance of improvement – nearly two-thirds of those studied – there was little or no variation between hospitals or surgeons.


A PRO Prediction Tool


In recent years, PROs have become an important focus of efforts to assess the quality and outcomes of medical care. “Differences in PROs after accounting for patient factors across hospitals and surgeons could indicate variation in health care system performance and an opportunity for quality improvement,” according to the authors.

At first glance, PROs for patients undergoing spinal fusion surgery seem to vary substantially between hospitals and surgeons. But the variation is greatly decreased after accounting for patient and surgical factors, “suggesting that patient characteristics are the main drivers of variability in functional response among lumbar fusion patients,” Dr. Flum and colleagues write. They have developed a PRO Prediction Tool to help predict which patients are more or less likely have improved function and decreased disability after lumbar spinal fusion. [1]

“Our study demonstrated that the overall variability was mainly driven by patient characteristics, suggesting that quality improvement efforts to reduce variation and improve overall functional outcomes may be better if focused at the patient level,” the researchers conclude. For example, selecting patients more likely to have favorable outcomes would increase the success rate of spinal fusion – but would greatly reduce the volume of procedures performed.

“Spine surgeons asked for tools that would help them to ‘pick the winners,’ and our PRO prediction tool does suggest there is a group that is much more likely to have better outcomes,” Dr. Flum said.

“Unfortunately, these data suggest that if surgeons want to increase the response rate by avoiding operation on patients with less than 50% chance of improvement, they may need to stop operating on around 60% of the patients they usually perform fusions on.”



Khor S, Lavallee DC, Cizik AM, et al. Hospital and surgeon variation in patient-reported functional outcomes after lumbar spine fusion: a statewide evaluation. Spine (Phila Pa 1976). 2019 Dec 4. doi: 10.1097/BRS.0000000000003299. [Epub ahead of print]



  1. Khor S, Lavallee D, Cizik AM, et al. Development and validation of a prediction model for pain and functional outcomes after lumbar spine surgery. JAMA Surg. 2018 Jul 1;153(7):634-642. doi: 10.1001/jamasurg.2018.0072.

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