J Arthroplasty. 2017 Jun;32(6):2033. doi: 10.1016/j.arth.2017.02.050.

# Letter to the Editor on ‘The Prevalence of Positive Findings on Metal Artifact Reduction Sequence Magnetic Resonance Imaging in Metal-on-Metal Total Hip Arthroplasty’: Part 1.

Reito A, Lainiala O, Eskelinen A.

We read with great interest the article by Lindgren et al [1]. The authors use ordinal logistic regression (OLR) to correlate predictor variables against primary outcome variables. OLR is used to report proportional odds ratios which authors do not report. The interpretation of the proportional odds ratios relies on the proportional odds (PO) assumption, which is the most important underlying assumption when performing OLR. The PO assumption relies on the equal relationships between each pair of outcome groups. This means that predictor coefficients that describe the relationship between absent pseudotumor (PT) and type I/II/III PT are the same as those that describe the relationship between absent PT/type I and type II/III.