Comparison of cost and complication rates for profiling hospital performance in lumbar fusion for spondylolisthesis

Background context: There is growing interest among payers in profiling hospital value and quality-of-care, including both the cost and safety of common surgeries, such as lumbar fusion. Nonetheless, there is sparse evidence describing the statistical reliability of such measures when applied to lumbar fusion for spondylolisthesis.

Purpose: To evaluate the reliability of 90-day inpatient hospital costs, overall complications, and rates of serious complications for profiling hospital performance in lumbar fusion surgery for spondylolisthesis.

Study design/setting: Data for this analysis came from State Inpatient Databases from nine states made available through the Healthcare Cost and Utilization Project.

Patient sample: Patients undergoing elective lumbar spine fusion for spondylolisthesis from 2010 to 2017 in participating states.

Outcome measures: Statistical reliability, defined as the ability to distinguish true performance differences across hospitals relative to statistical noise. Reliability was assessed separately for 90-day inpatient costs (standardized across years to 2019 dollars), overall complications, and serious complication rates.

Methods: Statistical reliability was measured as the amount of variation between hospitals relative to the total amount of variation for each measure. Total variation includes both between-hospital variation ("signal") and within-hospital variation ("statistical noise"). Thus, reliability equals signal over (signal plus noise) and ranges from 0 to 1. To adjust for differences in patient-level risk and procedural characteristics, hierarchical linear and logistic regression models were created for the cost and complication outcomes. Random hospital intercepts were used to assess between-hospital variation. We evaluated the reliability of each measure by study year and examined the number of hospitals meeting different thresholds of reliability by year.

Results: We included a total of 66,571 elective lumbar fusion surgeries for spondylolisthesis performed at 244 hospitals during the study period. The mean 90-day hospital cost was $30,827 (2019 dollars). 12.0% of patients experienced a complication within 90 days of surgery, including 7.8% who had a serious complication. The median reliability of 90-day cost ranged from 0.97to 0.99 across study years, and there was a narrow distribution of reliability values. By comparison, the median reliability for the overall complication metric ranged from 0.22 to 0.44, and the reliability of the serious complication measure ranged from 0.30 to 0.49 across the study years. At least 96% of hospitals had high (> 0.7) reliability for cost in any year, whereas only 0-9% and 0-11% of hospitals reached this cutoff for the overall and serious complication rate in any year, respectively. By comparison, 10%-69% of hospitals per year achieved a more moderate threshold of 0.4 reliability for overall complications, compared to 21%-80% of hospitals who achieved this lower reliability threshold for serious complications.

Conclusions: 90-day inpatient costs are highly reliable for assessing variation across hospitals, whereas overall and serious complications are only moderately reliable for profiling performance. These results support the viability of emerging bundled payment programs that assume true differences in costs of care exist across hospitals.