Efficacy of repeat magnetic resonance imaging of the knee

A patient often initially presents to an orthopedic surgeon with the magnetic resonance image (MRI) ordered by his or her primary care physician in hand. Often, a significant period of time elapses after injury before the patient is assessed by the orthopedic surgeon; therefore, the initial MRI may be considered outdated because of a new injury or a change in symptoms or because the orthopedist may prefer a new study, a stronger magnet, or a special imaging protocol. However, the decision to repeat a knee MRI is presently an arbitrary one because no clinical guidelines exist to justify this practice. All repeat knee MRIs performed at our academic institution in the past 9 years were retrospectively examined. Inclusion criterion was repeat MRI of the same knee with no surgical intervention. The formal radiology reports were grouped into 3 categories: change, no change, and unclear. Knee pathology was further grouped into 6 categories indicating what specific structures were pathological or injured. Logistic regression analysis was used to test the association of time vs category or condition change between MRIs. Of 3501 knee MRI studies, 88 patients had a total of 101 repeat MRIs. The average number of days between repeats for those with category or condition change was 612 vs 504 for those with no change. Age, sex, and time between MRIs were not significantly associated with a category or condition change. Repeat knee MRI prior to surgical intervention is becoming more prevalent and may have clinical merit. A further prospective study is warranted.