The Metatarsal Cortical Index as an Indicator of Insufficiency Fracture of the Foot.

The diagnosis of metatarsal stress fractures is challenging. Standard imaging often shows false-negative results. The aim of this study was to create reliable radiologic outcome parameters to predict insufficiency fractures of the metatarsals. We performed an age- and sex-matched case-control study of patients with (n = 18) and without insufficiency fracture (n = 18) of the foot. The metatarsal cortical index (MCI) for each metatarsal was developed to predict an insufficiency fracture. The MCI of each metatarsal was significantly decreased in the insufficiency fracture group compared with the control group (p < .01). The MCI of the fourth ray yielded the highest area under the curve among the analyzed MCI values (area under the curve, 0.79; 95% confidence interval, 0.61-0.90). A cut-off value of 1.62 for the MCI of the fourth ray yielded a sensitivity of 78% and a specificity of 78% to predict insufficiency fracture of the foot (odds ratio, 12.25; 95% confidence interval, 2.54-58.97), and enabled accurate allocation to the insufficiency fracture group versus the control group in 74% of cases. In conclusion, a decreased MCI is associated with metatarsal insufficiency fractures and enables an accurate diagnosis in 3 out of 4 cases. The MCI might aid clinicians in identifying insufficiency fracture, and raise the suspicion of the diagnosis without additional imaging studies.