The cost-effectiveness of magnetic resonance imaging for patients with internal derangement of the knee

Magnetic resonance imaging (MRI) has excellent specificity and sensitivity for the diagnosis of internal derangement of the knee (IDK). The use of MRI to screen patients with suspected IDK could avoid unnecessary arthroscopie s with a reduction in costs. The purpose of this study was to evaluate the use of arthroscopy among patients with IDK, and to estimate the potential c ost-effectiveness of MRI in these patients to avoid unnecessary arthroscopi es. The study was based on a retrospective cohort of all patients attending three orthopedic clinics between April and September 1993 with a new diagn osis of IDK. Charts were reviewed in 1994 to allow for a follow-up of more than 6 months. An economic evaluation was performed based on cost-effective ness ratios (per averted arthroscopy), including direct and indirect costs. There were 241 patients with a new diagnosis of IDK (67% males, mean age 3 5 +/- 12 years), and 110 (46%) underwent arthroscopy. The remaining patient s received conservative therapy and were not scheduled for arthroscopy with in the period of observation. Using a priori established criteria, 10% of t he arthroscopies could be considered diagnostic only (e.g., normal knee) an d 27% were of doubtful efficacy from a therapeutic perspective (e.g., debri dement alone). Many of these arthroscopies could have been avoided by perfo rming a prior MRI. Using these findings, we conducted decision tree analyse s of the use of MRI among patients requiring arthroscopy of the knee. A sen sitivity analysis was performed to evaluate the various model assumptions. In general, MRI appeared to be a cost-effective diagnostic procedure for pa tients with IDK requiring arthroscopy of the knee, and there were cost savi ngs associated with it in some of the models tested.