Diagnostic Performance of a Gravity Varus Stress CT Protocol in Detecting Instability in Isolated Coronoid Fractures.

Abstract

Instability associated with isolated coronoid fractures can be subtle and frequently missed on routine imaging. A stress-based CT protocol may improve detection of occult instability in isolated coronoid fractures. The purpose of this study was to evaluate the diagnostic performance of a gravity varus stress CT protocol in detecting instability in isolated coronoid fractures and compare it with routine static CT. A retrospective cohort study of patients with isolated coronoid fractures who underwent either gravity varus stress CT or routine static CT between 2019-2025 was performed at two academic centers. Instability was assessed via clinical examination or fluoroscopic examination under anesthesia (EUA). CT findings were correlated with the reference clinical examination or EUA to calculate positive predictive value (PPV) and false-negative rate (FNR). Fisher's exact test was used for between-group comparisons. Eighty-four patients were included (41 stress CT, 43 static CT). Gravity varus stress CT demonstrated instability in 26/41 patients, with clinical or intraoperative instability confirmed in 28/41, yielding a PPV of 96% and FNR of 11%. Static CT demonstrated instability in 5/43 patients, while clinical or intraoperative assessment confirmed instability in 28/43, yielding a PPV of 100% and FNR of 82%. There was no difference in PPV (p = 1.00), but gravity varus stress CT had a significantly lower FNR than static CT (p < 0.001). Routine static CT substantially underestimates instability in isolated coronoid fractures. Gravity varus stress CT provides a more accurate assessment, with markedly lower false-negative rates and excellent positive predictive value. Stress CT should be considered in the evaluation of isolated coronoid fractures without obvious history/imaging evidence of dislocation.