Metal-on-Metal Hip Replacement: MRI Signal Intensities of Different Body Tissues and Their Relations to Blood Metal Ion Levels.

BACKGROUND: Metal-on-metal total hip prostheses (MoM-THR) have been shown to produce hypersensitivity reactions and fluid collection (pseudotumor) by the hip as well as high blood metal ions levels (BMILs).

OBJECTIVES: To evaluate the magnetic resonance imaging (MRI) signal-to-noise ratio (S/N) in selected body tissues around the hip of patients who underwent MoM hip replacement and to correlate to BMILs.

METHODS: Sixty-one MRI hip examinations in 54 post-MoM-THR patients (18 males, 36 females, mean age 65 years) were retrospectively evaluated independently by two readers. The mean S/N ratio in a region of interest was calculated for periprosthetic pseudotumor collection (PPC), the bladder, fat, and muscle on axial T1w, FSE-T2w, and short tau inversion recovery (STIR) sequences on the same location. BMILs were retrieved from patient files.

RESULTS: PPC was detected in 32 patients (52%) with an average volume of 82.48 mm3. BMIL did not correlate with the presence of PPCs but positively correlated with the PPC's volume. A trend for positive correlation was found between BMILs and S/N levels of STIR images for muscle and bladder as well as for PPC and cobalt levels. A trend for correlation was also seen between BMIL with PPC's T1 w S/N.

CONCLUSIONS: Alteration of MRI S/N for different hip tissues showed a tendency for correlation with BMILs, possibly suggesting that metal deposition occurs in the PPC as well as in the surrounding tissues and bladder.