Prior X-Ray and Diagnostic Yield of Knee MRI: A Retrospective Study of Imaging Pathways and Healthcare Utilization

Purpose: Variation in knee MRI diagnostic yield is often interpreted as reflecting imaging effectiveness. However, in real-world healthcare systems, diagnostic yield may instead be driven by referral behavior and patient selection. Understanding this distinction is essential for evaluating imaging utilization, healthcare efficiency, and potential overuse of advanced imaging. This study examines whether differences in MRI yield reflect imaging pathways or underlying referral patterns in routine clinical practice. Materials and Methods: This retrospective cohort study included consecutive patients undergoing knee MRI between January 2020 and December 2024. Patients with red flag indications were excluded to focus on discretionary imaging. The primary outcome was clinically relevant MRI findings based on final report impressions. The primary exposure was prior X-ray before MRI. Multivariable logistic regression was used for adjusted analysis, including age, sex, trauma status, mechanical symptoms, and symptom duration. Results: Among 486 patients, 59.5% had prior X-ray. Clinically relevant MRI findings were less frequent among patients with prior X-ray (40.1%) than among those without (49.7%), corresponding to an absolute difference of 9.6%. After adjustment for sex and clinical covariates, prior X-ray showed lower odds of clinically relevant findings, although this association was attenuated and no longer statistically significant (aOR 0.74, 95% CI 0.50–1.10; p = 0.138). Male sex was independently associated with higher odds of clinically relevant MRI findings (aOR 2.48, 95% CI 1.61–3.83; p < 0.001). Formal interaction testing did not demonstrate significant effect modification by trauma status (p = 0.317). These findings suggest that variation in MRI yield may reflect differences in referral pathways, patient selection, and healthcare utilization patterns. Conclusions: MRI yield in routine practice may be influenced by differences in clinical context and referral-related patient selection. Further studies are needed to better understand the contribution of imaging pathways to observed variation in diagnostic yield.