# Beyond raw comparisons: Adjusted analysis reveals only minor inter-hospital differences in ACDF outcomes in Norway

## TL;DR

A study in Norway found that differences in spine surgery outcomes between hospitals are mostly due to patient factors, not hospital quality, after adjusting for risk factors.

## Contribution

The study demonstrates that risk-adjusted analysis significantly reduces perceived inter-hospital variation in ACDF outcomes.

## Key findings

- Unadjusted data showed up to 25% variation in non-successful outcomes between hospitals.
- After risk adjustment, inter-hospital differences in outcomes were minimal (1.9%–3.6%).
- Private sector status remained statistically significant in all outcome models.

## Abstract

Annual reports from the Norwegian Registry for Spine Surgery (NORspine) suggest notable inter-hospital variation in patient-reported outcomes after anterior cervical discectomy and fusion (ACDF) for radiculopathy.

Do unadjusted comparisons not account for differences in case mix between institutions?

This multicenter observational cohort study analyzed data from 7832 patients undergoing ACDF for cervical radiculopathy in Norway between 2014 and 2023. Risk factors for poor outcome were identified by multivariate logistic regression. Outcomes were measured using the Neck Disability Index (NDI), Numeric Rating Scale (NRS) for arm pain, and EQ-5D-5L at 12 months. The proportion of non-successful outcomes for five public hospitals and the private sector was adjusted for patient demographics and risk factors.

Unadjusted, the range of non-successful outcomes between hospitals was up to 25%. After risk adjustment, inter-hospital differences diminished markedly (range 1.9%–3.6%). Only private sector status remained statistically significant in all three models. High odds ratios (>2.0) for non-success were observed for medical litigation, prior cervical surgery, duration of arm pain >12 months, and headache as a dominant symptom.

Apparent differences in ACDF outcomes across Norwegian hospitals were largely explained by patient-related risk factors. Adjusted analyses revealed only minor inter-hospital variations. For registry-based quality benchmarking, risk-adjusted reporting is essential to support transparent comparison and informed clinical decision-making.

•Logistic regression analysis revealed several predictors of poor outcome 12 months after ACDF surgery.•Risk factor adjusted analysis of outcome data reduces variation between hospitals significantly.•Quality registries should publish both adjusted and unadjusted data to enable transparent hospital comparisons.

Logistic regression analysis revealed several predictors of poor outcome 12 months after ACDF surgery.

Risk factor adjusted analysis of outcome data reduces variation between hospitals significantly.

Quality registries should publish both adjusted and unadjusted data to enable transparent hospital comparisons.