Post-traumatic knee MRI findings and associations with patient, trauma, and clinical characteristics: a subgroup analysis in primary care in the Netherlands

Kim van Oudenaarde, Nynke M Swart, Johan L Bloem, Sita Ma Bierma-Zeinstra, Paul R Algra, Bart Koes, Jan Verhaar, Rob Ghh Nelissen, Patrick Je Bindels, Pim Aj Luijsterburg, Monique Reijnierse

The added value of magnetic resonance imaging (MRI) in primary care is still being debated. A high diagnostic yield can be expected in young and active patients with post-traumatic knee complaints. To determine the frequency of MRI abnormalities in young and active patients (aged 18-45 years) and the associations with patient, trauma, and clinical characteristics. A subgroup analysis of 174 patients, aged 18-45 years with knee trauma of <6 months, allocated to MRI in a randomised controlled trial on the yield of MRI in primary care. Patients were recruited by 150 GPs in the Netherlands from October 2012 to November 2015. Associations were expressed using mean differences, odds ratio (OR) and predictive values. Sixty-seven out of 174 patients (39%) had a positive MRI finding, predominantly anterior cruciate ligament (ACL) ruptures (22%) and/or traumatic meniscal tears (15%). Patients with a pre-existing musculoskeletal comorbidity had a two-fold lower prevalence of positive MRI findings (21%), OR 3.0 (95% confidence interval [CI] = 1.3 to 7.0). A 'sports related trauma' showed the highest OR of 4.6 (95% CI = 2.2 to 9.3) for a positive MRI finding. Clinical scores were statistically, significantly worse in patients with positive MRI findings, with mean differences ranging from 10 to 20%. Furthermore, increasing duration of complaints was correlated with decreasing prevalence rates of positive MRI findings. Overall, a popping sound and direct swelling showed the highest positive predictive value of 65% for the presence of positive MRI findings. The results from this study enable a preselection of patients to increase the diagnostic yield of MRI in primary care.